Tuesday, 27 October 2020, 12:51 AM
Site: IMI eLearning
Course: IMI eLearning (IMI eLearning)
Glossary: Automotive Glossary
2

2K

The common descriptive title for paints that require the addition of a hardener (without which they will not cure).
A

A.B.S

Anti-lock braking system.

A.P.I.

American Petroleum Institute.

A.P.I. (C)

American Petroleum Institute classification for oils suitable for diesel (compression ignition engines).

A.P.I. (S)

American Petroleum Institute classification for oils suitable for gasoline (spark ignition) engines.

A.P.I. SC/CC

Engine lubricating oil classification suitable for basic petrol and diesel engines.

A.P.I. SG/CD

Engine lubricating oil classification suitable for modern engines.

A/C

Air Conditioning

A/C - Air Conditioning

Air conditioning system that uses a refrigerant to remove heat from the air entering the passenger compartment.

A/D Converter

An electronic device used to convert analog values to digital signals for electronic control units and instruments.

A/F

Air/Fuel Ratio

A/T

Automatic transmission.

Abandon

The term used when a test cannot be completed because the NT considers it unsafe to continue or because it becomes apparent during the test that certain items cannot be satisfactorily inspected. An appropriate fee may be charged for the test.

Abort

The term used when a test cannot be completed because of a problem with the VTS’s/DC’s testing equipment or the NT. No fee may be charged for the test.

Abrasion

Wearing away of a surface by some external force, such as sanding.

Abrasive

Substance used to wear away or smooth a surface by friction.

Abrasives

Substances used to wear away a surface by friction.

ABS

Antilock braking system.

Absolute Pressure

The pressure that exists when the forces of gravity are excluded from the actual pressure. Absolute pressure is equal to gauge pressure plus atmospheric pressure.

Absorb

The penetration of a solid substance by a liquid as by capillary, osmotic, solvent, or chemical action.

Absorption

Of heat: Takes in heat energy. Of sound: Takes in sound energy.

ABSV

Air Bypass Solenoid Valve

AC

Alternating Current

AC - Alternating Current

An electrical current that flows in forward and reverse bias alternately.

Accelerate

To speed up a process.

Acceleration

Increasing velocity or speed.

Accelerator

A substance that, when added to a paint, will speed up the rate of cure.

Accelerator Pump

Carburettor pumping system that introduces flow of fuel into the carburettor choke (venturi) on acceleration, particularly when accelerating from low speeds.

Accumulator

A hydraulic device that dampens the pulses and retains a residual pressure in a hydraulic circuit.

Accuracy

How close the data given is to the true value.

ACEA

Association des Constructeurs Europeens d'Automobiles. The European organisation that sets specifications for lubricants. There are three categories for engine oils. A for gasoline/petrol engines. B for light vehicle diesel engines. C for commercial vehicle diesel engines.

Acetone

A very fast evaporating solvent with high solvency for certain types of compounds and resins. Has a characteristic ether-like odour.

Acid

An inorganic or organic compound that (1) reacts with metals to yield hydrogen; (2) reacts with a base to form a salt. They are corrosive to human tissue and should be handled with care. Examples are hydrochloric acid, sulphuric acid, and nitric acid.

Acid Rain

Forms when pollution is combined with water in the atmosphere. When sulphur dioxide and nitrogen oxides mix with water molecules, they form weak sulphuric and nitric acids. As the water evaporates, the acids gain strength and can etch the finish of any vehicle upon which they have been deposited.

Acidic Compounds

Harmful chemicals that are formed during combustion and can contaminate engine oil. Sulphur in fuel can form sulphuric acid which can cause corrosion, sludging and lubricating oil defects.

Ackerman Principle

System of steering that produces wheel turning axes around a common point.

Acrylic

A coating based on a polymer containing short chain esters of acrylic and methacrylic acid. One-pack Acrylics were once widely used as automotive topcoats, but have generally been replaced by water-borne base colours overcoated with two-pack Acrylic clear coats

Acrylic Urethane

A coating based on urethane chemistry which also includes acrylic chemistry as part of the cross-linked polymer backbone.

ACS

Air conditioning switch.

ACT - Air Charge Temperature

Air charge temperature sensor measures the intake air temperature on fuel injection systems.

Activator

A necessary component used to provide a chemical reaction to cure paints, resins and adhesives.

Active

A system that takes action all the time as opposed to a passive system that waits for a specific event before reacting.

ACTS

Air Charge Temperature Sensor

Actuators

Electronic components that receive signals from an electronic control unit (ECU) and operate to make a system work.

Adapter

General term used to describe a device that allows one component to fit with another.

Adaptive Memory

A computer memory process that allows for changes in an open-loop mode.

Additive

A chemical added to improve the properties or performance of something.

Additives

Chemical substances added to paint products in relatively small amounts to impart or improve desirable properties. Examples include UV screeners, flow agents, and fish eye eliminators.

Adhesion

The phenomenon by which one material is attached to another by means of surface attraction.

Adjuster

General term used to describe a component that changes the adjustment of something (brake shoes or brake bands for example).

Advice

Guidance offered by someone.

AE

Authorised Examiner – the organisation that operates and manages one or more VTSs and is responsible for controlling the quality of testing carried out. Except in the case of a ‘sole trader’ the AE is not a person but a legal entity (e.g. a company or partnership).

Aeration

Air mixture in a hydraulic liquid that reduces the performance of a hydraulic system.

Aesthetic Value

A value put on how nice or appealing something looks.

AFC

Air Flow Control

AFM

Air Flow Meter

AFS

Air Flow Sensor

Agglomerate

Clumps of pigment particles which have formed loose clusters. Usually undesirable in paint, since agglomerates tend to settle out and exhibit poor colour or 'seeds', which are small granular deposits, other than dust, found in paint, varnish or lacquer colour.

Agitator

A paint stirrer.

Agitator Cup

Paint cup used with high metallics and pearls to keep the pigment particles in suspension by continually mixing the paint. This ensures better colour uniformity.

Air Bleed Valve

An automatic device used on fuel injection systems to provide fast idle during cold start and warm up.

Air Cap

Fitted in front of a spray gun fluid nozzle to direct compressed air against the paint to form and shape an atomised cloud of droplets.

Air Charge

Description of the amount of air taken into an engine on the induction stroke.

Air Cleaners/Filters

Canisters holding paper, plastic foam or gauze elements to trap dirt and grit.

Air Dry

The ability of a coating to dry or cure to its ultimate hardness under normal atmospheric conditions, without baking or force-drying. Measurement of time required must state conditions such as temperature and humidity.

Air Flow

Movement of a quantity of air past a point in a set time.

Air Flow Meter

Provides information to fuel injection system electronic control unit (ECU) on engine load. Measures the mass of air entering an engine.

Air Flow Sensor Plate

A plate used to sense the movement of air and therefore control fuel quantity.

Air Gap

The gap between two parts of a component, such as the spark plug electrodes, an inductive sensor or an armature and field shoes of a motor or generator.

Air Horn

The air inlet side of a carburettor or throttle body assembly.

Air Injection

An emission control device that adds air to the exhaust to add oxygen for the conversion of hydrocarbons and carbon monoxide to water and carbon dioxide. Usually fitted upstream of a catalytic converter.

Air Intake Duct

A pipe or similar used as part of the intake manifold or general system.

Air Line

A pipe that delivers compressed air.

Air Lock

A bubble of air in a hydraulic system that can be compressed and therefore reduces the performance or causes failure of the system.

Air Ratchet

A ratchet wrench driven by compressed air.

Air Resistance

Friction force caused by, for example, a vehicle moving through the air.

Air Spray

A system of applying paint in the form of tiny droplets. The paint is broken into droplets (atomised) by a spray gun as a result of being forced into a high velocity air stream. The shape and paint density of the resulting droplet cloud can be controlled by variations in air pressure, paint viscosity and gun tip geometry.

Air Temperature Sensor

Electronic device that provides information for engine management systems and frost warning indicator.

Air-fuel Ratio

The air and fuel mixture strength ratio.

Airflow Meter

Provides information to fuel injection system electronic control unit (ECU) on engine load. Measures the mass of air entering an engine.

Airflow Sensor Plate

Mechanical fuel injection component that moves in proportion to the air intake and sets fuelling accordingly.

Airless Spray

A system of applying paint in which the paint, under extremely high pressure, is passed through a nozzle and breaks up into droplets as it enters the lower pressure region outside the gun tip.

Airline

A pipe that delivers compressed air.

ALCL

Assembly Line Communications Link

ALCL/ALDL

Assembly line communication or diagnostic link. A multisocket connector for attaching a diagnostic tool to a vehicle electronic system.

Alcoholics Anonymous

A worldwide group of men and women who meet in order to help one another stop drinking alcohol and remain sober.

ALDL

Assembly Line Data Link

Alignment

Bringing into line.

Alkali

A chemical 'base' (loosely, the opposite of an acid). Certain types of alkalis have been used as fuel cell electrolytes.

Alkyd

A coating based on a polyester binder. Such polyesters are chemical combinations of molecules that contain more than one acid or alcohol group.

Allen

A name used to describe a hexagonal key.

Alloy

A mixture of metals and other elements to form a metal with specific properties such as phosphor bronze used for bushes.

Alternative fuel

A fuel used in vehicles that comes from a source other than petroleum, such as ethanol made from corn and biodiesel made from vegetable oil.

Alternator

An electrical generator attached to and driven by a motor vehicle engine.

Alternator Brushes

Soft carbon brushes that conduct electricity to the field windings via the slip rings.

Aluminium

Non-ferrous metal used as a substrate or a pigment.

Aluminium Oxide

Sharp and hard abrasive - used in dry-flatting Production papers

Ambient Pressure

Air pressure in the surrounding area.

Ambient Temperature

Temperature of the air surrounding an object.

Ammeter

Instrument for measuring electrical current.

Ammonia

A compound of nitrogen and hydrogen with the formula NH3. It is normally encountered as a gas with a characteristic pungent odour but can be included in a water based form into cleaning compounds for example.

Amperage

Strength of an electrical current in amperes.

Ampere (Amp)

Electrical unit for measuring the flow of electricity in a circuit.

Ampere-hour-rate

Discharge rate used to describe what a battery will produce. For example, a 40Ah battery will produce 2A for 20Hrs. The 20hrs is an agreed value used to allow comparisons to be made.

Amplification

An increased electrical voltage and/or current compared to say the original signal.

Amplifier

An electronic device that increases or allows an increased electrical voltage and/or current to flow.

Amplitude

The maximum distance moved by a point on a vibrating body or wave measured from its equilibrium position. It is equal to one-half the length of the vibration path i.e. half the peak to peak value of a wave.

Amps

Short for Ampere (unit of electrical current)

Anaerobic

Used to describe a sealant that dries when air or oxygen is excluded.

Analog

A measuring process that uses a variable electrical current to provide a signal for computers and instruments.

Analog Gauge

An instrument readout that displays using a moving needle or similar method.

Analogue

A measuring process that uses a variable electrical current to provide a signal for computers and instruments.

Analogue Gauge

An instrument readout that displays using a moving needle or similar method.

Anionic Electrodeposition

One of the electro-coating methods in which the body is charged positively and completely immersed in the negatively charged paint. Frequently used for OEM primer application, the resultant coating is known as 'E-coat'

Annual Income

Amount of money you earn each year.

Annulus

The outer gear with internal teeth on an epicyclic gear train.

Anode

A positive connection.

Anodised Aluminium

A surface treatment for aluminium that adds an oxidised coating to harden the surface of the component.

Anodising

An electrolytic surface treatment for aluminium which builds up an aluminium oxide coating, to provide better adhesion.

Anti-corrosive

Protective coating applied on metal surfaces to prevent corrosion.

Anti-freeze

A chemical such as ethylene glycol, added to the cooling water of an engine to lower the freezing point for winter operation.

Anti-knock

Usually used to refer to an additive that is added to fuel, which makes the burning process more controllable, resulting in reduced tendency to knock.

Anti-roll Bars

Suspension component that reduces vehicle roll.

Anti-skinning Agents

Chemicals added to a paint to help prevent the formation of a surface film during storage.

Anti-trap Function

Facility to prevent electric windows closing and trapping something - your fingers for example! See also Bounce Back.

Antifreeze

Additive put in the cooling system to prevent freezing.

Antimony

A metal, which is added to lead, to improve its mechanical strength. Batteries were traditionally constructed with lead-antimony.

Antivirus Software

A software package that prevents computer viruses from damaging or destroying the system.

Application

Another name for a computer program such as Microsoft Word.

Applied Solids

Solids that remain on the substrate being coated or painted.

APS

Absolute Pressure Sensor

APS - Absolute Pressure Sensor

A barometric pressure sensor used to compare atmospheric and manifold pressures in electric fuel injection systems.

Aquaplaning

The effect when a vehicle's tyres tend to skid on top of water on the road.

Aqueous

Describes a water-based solution or suspension (see 'waterborne').

Arcing

Conduction of electricity across a gap. An arc is caused as contacts open.

Area

Length x width

Armature

Electrical windings around the core fixed to the spindle of a motor or dynamo.

Aroma

The smell of something such as perfume or worse...

Aromatics

A type of solvent based on benzene ring molecules.

Asbestos

Fibrous silicate material that can be woven into an incombustible fabric. Requires special handling as it is a hazardous substance.

ASDM

Airbag System Diagnostic Module

Aspect Ratio

Ratio of two axes at right angles to each other such as the long and short sides of a rectangle. When applied to low profile tyres it refers to the width and depth and is shown as a percentage value in the tyre size marking.

Aspiration

Breathing or induction process of an engine. Non-turbocharged engines may be described as naturally aspirated.

Assessor

The teacher or tutor, who assesses the portfolio of evidence.

Asymmetrical

A description of objects that are different on each side of their centre line.

ATDC

After Top Dead Centre

ATDC - After Top Dead Center

ATDC - Before Top Dead Centre.

ATDC - After Top Dead Centre

The position of the crankshaft when the piston has passed the top of the cylinder and is on the way down.

ATF

Automatic Transmission Fluid.

ATL

Automated Test Lane – These are lanes authorised by VOSA of use in the automated mode.

Atmosphere

The air that surrounds the Earth's surface.

Atmospheric Pressure

Pressure in the atmosphere produced as a result of the Earth's gravity. Measured at sea level it has a value of 1 Bar, 14.7 psi or 100 kPa.

Atom

Smallest particle in a chemical element that can take part in a chemical reaction. A single particle of an element.

Atomic

Relating to the atom...

Atomic clock

This is a type of clock that uses an atomic resonance frequency standard as its timekeeping element. It is very accurate.

Atomisation

The formation of tiny droplets of liquid as in the paint spraying process. Atomisation is usually achieved by turbulence in an air stream, or a sudden drop in pressure.

Atomised

The stage in which the metered air/fuel emulsion is drawn in to the airstream in the form of tiny droplets.

Atomization

Breaking up of fuel into fine particles during induction into an engine.

Atomized

The stage in which the metered air/fuel emulsion is drawn in to the airstream in the form of tiny droplets.

ATS

Air Temperature Sensor

Aural

Of or relating to the ear or to the sense of hearing - aural diagnostics mean listening for faults such as a bearing noise or a misfire

Auto-box

See Automatic Transmission

Automatic Adjusters

Brake components that automatically take up wear to keep brake shoes or pads close to the drum or rotor.

Automatic Choke

A carburettor component using a bimetallic strip that operates at low engine temperatures to improve cold start and idle performance. Operates independently of the driver.

Automatic Transmission

A vehicle gearbox with automatic gear shifts based on engine speed and load conditions. Does not require individual gear shifts by the driver.

Auxiliary Air Flow

Used to describe a flow of air that bypasses the normal route. It is used to control idle speed or idle mixture.

Auxiliary Air Valve

A valve used to control auxiliary air flow.

Auxiliary Components

Components that are outside a specific system. For example, when working on the engine, an alternator would be described as auxiliary.

Auxiliary Lights

Extra, non-essential lights such as front spotlights or driving lights.

Auxiliary shafts

Shafts that are used on some engines for balance or to drive other components.

Avalanche Diode

A diode that conducts when a value voltage is applied. Used to protect circuits from overload.

Average

The sum divided by the number of items.

Awarding body

There are several awarding bodies City and Guilds: AQA, Edexcel and OCR for example.

AWD

Transmission system that uses all four wheels of a vehicle to provide a drive. This term is usually used on vehicles with a permanent four wheel drive that transfers drive to another axle when some loss of drive occurs on the main drive axle. The term 4WD or 4x4 is used for used for vehicles with selectable four wheel drive.

AWD - All Wheel Drive

Transmission system that uses all four wheels of a vehicle to provide a drive. This term is usually used on vehicles with a permanent four wheel drive that transfers drive to another axle when some loss of drive occurs on the main drive axle. The term 4WD or 4x4 is used for vehicles with selectable four wheel drive.

Axial Loading

Along the axis of a shaft.

Axial Motion

Movement along or parallel to the axis of a shaft.

Axis

The centre line through a shaft or axle. The centre about which an object rotates or where the object is in equilibrium.

Axle

Horizontal transverse shaft or beam with spindles on which road wheels are mounted.

Axle Loading

Term used to describe the forces acting on an axle.

Axle Mounting

Method of fixing the axle to the body or springs.

Axle Stands

Vehicle support equipment manufactured with a rated weight capacity. Used to support a vehicle when wheels are removed or when access to the underside is needed. Also known as jack stands.

Axle Windup

A condition in an axle where the driven component locks and the axle casing attempts to rotate on its mountings. Usually caused when a differential lock or limited slip device is used and wheel spin is not possible such as on a dry road.
B

B-CAN

Body CAN or Basic CAN

B.A

British Association old standard size of threads."

B.S. Kite Mark

British Standards Kite Mark. The symbol of the British Standards Institute consisting of a triangle on its point with a capital B on its side above the triangle and a capital S inside the triangle.

B.S.F

British Standard Fine size of thread."

B+

Battery Positive Voltage

Babbitt Metal

An alloy of tin, copper, antimony and lead used as a coating for plain steel bearings.

Back EMF

A voltage produced that tends to oppose the voltage that created it.

Back Plate

(1) Non-rotating plate carrying the shoes of a drum brake. (2) Metal member carrying friction material of the disc brake pad.

Back Pressure

The pressure build-up in the exhaust caused by the resistance to exhaust flow by pipe diameters and muffler baffles. Used in design to balance an exhaust to an engine.

Back-Sanding

Technique of sanding a surface to taper the paint film away from the metal repaired area.

Backfire

Combustion of fuel in the intake or exhaust resulting in a loud explosive noise.

Backing

The base material of flatting paper onto which abrasive grains are coated. For masking tape, the backing is the paper section without the adhesive.

Backing Pad

A supporting pad for abrasive disc and/or polishing pads that is attached to a polishing mop or a DA sander. In the compounding, glazing or polishing operation, a foam or wool polishing or glazing pad is attached on top of the backup pad. In dry sanding operations an abrasive disc is attached to the face of the pad.

Backlash

The clearance between two components, usually used to measure the running clearance of gear teeth.

Backup

A second copy of work in case the original is damaged or destroyed. Should be stored away from the computer.

Baffle

A part fitted behind the air cap in a spray gun to direct the air stream and reduce air turbulence.

Baking

Application of heat to cure and dry a coating. In automotive refinishing, baking is used to speed up the drying of air-drying finishes and is sometimes called force-drying. The metal temperature in refinish baking usually does not exceed 80°C (180°F).

Balance Shaft

A rotating shaft geared to another shaft, usually the crankshaft that carries counterbalance weights to bring the shafts into harmonic balance.

Balance Valve

A hydraulic device that controls the pressure in different parts of a hydraulic circuit. Used to balance front and rear brake actuation.

Balance Weights

Small weights used to balance a shaft or a wheel.

Balancer

Additive used to balance colour formulae in proportion to size and pigment-to-binder ratio.

Balk Ring

A component of a synchromesh gear hub that provides a cone clutch and guidance of the outer hub to the gear dog teeth.

Ball Bearing

A bearing consisting of inner and outer tracks with a series of ball bearings in between. A single surface hardened steel ball.

Ball Flange

Flexible exhaust connection.

Ball Joints

Joints that allow movement for suspension and steering.

Ball Pivot

A pivot that allows movement in several directions.

Ball Valve

A simple valve that is closed off as a ball moves.

Ballast Resistor

Electrical resistor used in low tension circuit to regulate ignition coil output when the engine is running and is by-passed during starting to give an increased spark voltage for cold starting.

Bandwidth

The maximum amount of information (bits/second) that can be transmitted along a channel.

Banjo Joint

A hydraulic joint consisting of a hollow through bolt and a hose connector that looks like a banjo and from which it gets its name.

Bar

Measurement of pressure - one atmosphere.

BARO

Barometric Pressure

BARO (Barometric Pressure)

Air or gas pressure measured in a standard unit. (Pascal, psi, bar)

Barrier Cream

Used to help prevent skin damage when working, for example, with oils.

Base

Terminal of a transistor that becomes conductive to the emitter when energised. The trigger terminal of transistors and thyristors.

Basecoat

A colour coat requiring final protection in the form of a sprayed clearcoat. The basecoat provides colour effects and appearance, while the clearcoat provides gloss as well as UV and chemical resistance.

Basic skills

Reading, writing, speaking in English (or Welsh) and using numbers sufficiently well to be able to function in society and at work. Key skills and basic skills overlap at levels 1 and 2.

BAT

Battery

Bath tub

An old type of combustion chamber looking like a bath tub when the cylinder head is turned over.

Battery

A chemical device that will give out an electrical current when connected into a circuit.

Battery Carrier

A tray to hold the battery, usually under the bonnet.

Battery Grease

Petroleum jelly used on battery terminals.

Battery module

A generic term meaning a collection of battery cells and control systems. Often relates to EVs or HEVs.

Battery Posts

The main connections on a battery.

Battery terminal

See Battery Post

Battery Volts

A term used to describe the voltage of the particular system. This is often 12V - but could be 14V when the engine is running.

BCM

Body Control Module

BDC

Bottom dead centre. The position of the crankshaft when the piston is at its lowest position in the cylinder. The crankshaft is at 180° of rotation from the top dead centre 0° position.

Bead

Part of the tyre.

Beam Axle

Type of non-independent suspension.

Beam Setter

Equipment used to check the alignment of vehicle headlights.

Bearing Cap

Half-round parts that holds the big end and main bearings into place either on the con rods or engine block.

Bearing Clearance

The freeplay between a bearing shell and journal.

Bearing Nip or Crush

Applies to the applied grip of a split shell bearing when the two halves are tightened together.

Bearings

Components used to support a shaft and allow rotation.

Bell Housing

Cover over the clutch assembly. Usually joins the gearbox to the engine.

Benign

A benign condition is one that is not usually serious or harmful. Zero emissions for example.

Benzole

Hydrocarbon fuel additive and octane improver.

Bevel Gears

Gears cut at an angle from the periphery so that they can transmit a drive through an angle. An example is the final drive crown wheel and pinion.

BHP

Brake Horse Power

Bi-Metal Spring

A spring made of two metals that expand differently with temperature change. This changes the tension as temperature changes.

Bias

Towards one side or one polarity.

Biased

Favouring one thing over another.

Big End

End of the con rod that fits to the crankshaft.

Big End Bearings

The journals and shell bearings on a crankshaft that carry the big ends of the connecting rods.

Bimetal Strip

Two metals bonded together so that when heated, the different rates of expansion cause the strip to bend. The amount of bend is proportional to the temperature.

Bimetal Thermostatic Spring

A spring that changes tension with temperature.

Bimetalic Valve

See Bi-metalic Valve.

Bimetallic Valve

A valve that operates when a temperature change moves a bimetal strip.

Binary

A system of numbering using 0 and 1 and used in computer operating systems.

Binary Counter

An electronic device that counts in binary (1s and 0s) by using logic gates and basic memory devices.

Binary digit

A binary digit or bit is the basic unit of information in computing and telecommunications; it is the amount of information that can be stored by a device or other physical system that can normally exist in only two distinct states - 1 or 0, on or off for example.

Binder

The component in a paint material that forms the film. So-called because it binds the pigment and any additives present into a solid durable film.

Binding

Term used to describe one component sticking or rubbing against another.

Biodegradability

The capacity of a material to decompose over time as a result of biological activity, especially to be broken down by microorganisms.

Bit

A binary digit or bit is the basic unit of information in computing and telecommunications; it is the amount of information that can be stored by a device or other physical system that can normally exist in only two distinct states - 1 or 0, on or off for example.

Black box

Equipment that records information about the performance of an aircraft during flight – or a vehicle during its normal use.

Blade Connector

An electrical cable connector consisting of a blade and spring sided socket.

Blanking Plugs

Screwed plugs used to blank off or block off a test port or adjustment point.

Bleed

The act of removing air from a liquid system.

Bleed Nipple

A small nipple valve that allows connection of a pipe and is operated by loosening.

Bleeding

A defect in which pigment from a lower coat of paint diffuses into an upper coat and discolours the latter. A non-bleeding colour is one that is not soluble in materials used over it and consequently does not work up into succeeding layers. Body filler may also cause bleeding if an excessive amount of hardener is added.

Blending

Repainting of panels or parts of panels and fading out the new colour onto adjacent prepared panel work to render the repair invisible. Normally only carried out on basecoat-and- clear finishes, as it is very difficult to blend a direct gloss paint finish.

Blending Flaps

Flaps used to mix hot/cold and fresh/recirculated air in a heater system.

Blipped Throttle

Description of a 'quick press' of the throttle to make the engine rev up.

Blistering

The development of hollow bubbles or water droplets in a paint film. Blistering is usually caused by the expansion of air or moisture trapped beneath the film. It can occur rapidly or any time after application as the paint film ages. Blistering may also occur from the presence of unreacted acid within the paint film.

Block diagram

A diagram of a system, in which the main parts or functions are represented by blocks connected by lines, which show the relationships between the blocks.

Blocker Bar

General term used to describe a bar that prevents an action of some kind.

Blooming

A powder-like deposit which sometimes forms on the surface of a paint. It is often the result of a solvent component partly dissolving the pigment(s) and then depositing them on the surface when the temperature is below the 'dew point',( i.e. the temperature at which moisture will condense on the surface)

Blow Back

Ignition of fuel in the inlet manifold causing a flame to rise out of the air intake through the carburettor.

Blower Motor

A motor that uses a fan to assist in moving air.

Bluetooth

Wireless Technology. A chip is responsible for the transmission of data between a wide range of devices (mobile phone and hands-free system) through short range digital two-way radio.

BlueVision

Trade name for 'blue' headlight bulbs produced by Philips.

Blushing

The appearance of whitish or "cloudy" areas in a paint finish, caused by absorption and retention of moisture in a drying paint film.

BMAP

Barometric/Manifold Absolute Pressure Sensor

Bodied Vehicles

A bodied vehicle is defined as ‘a vehicle with a structure consisting/comprising of a floor pan and panels which, with a roof fully encloses the vehicle occupants and without a roof encloses them other than where the roof would be’. As a guide, if the driver sits in the vehicle with surrounding structure it would be classed as bodied.

Body

Main portion of motor car.

Body Filler

A heavy-bodied 2K plastic filler material which cures very hard and is used to fill small dents in metal and plastic panel work.

Bodying

Thickening of paint in the can, usually due to evaporation of solvents or volatile material because of poor fitting lids or exposure to heat or air.

Bond

Attraction between two things such as to cause them to stick together.

Bonding Cables

Cables or wires used to connect different panels together.

Bonding Resin

Adhesive often used on friction linings.

BOO

Brake on/off switch

Boost Pressure

The amount of increase above atmospheric pressure provided by a supercharger.

Booster Fan

See blower motor.

Boot

Usually made of rubber, a cover for a moving component such as a track rod end.

Boots/Gaiters

A rubber (or similar) boot used to cover working components. It is used to keep dirt out and in some cases lubrication in place. Also slang for alligator...

Bore (cylinder)

The internal part of a hollow cylinder in which a piston is located.

Boring Bar

Used to cut cylinder bores.

Boron steel

Boron steels possess hardenability equivalent to that of much higher carbon steels and more expensive low alloy heat treatable steels. Tempering toughens boron steels. The addition of only 0.001-0.003% soluble boron to a suitably protected base steel can produce an increased hardenability compared other steels.

Bosch

Robert Bosch GmbH is a technology-based corporation which was founded by Robert Bosch in Stuttgart, Germany in 1886.

Boss

A reinforcing section around a cylindrical bore in a component.

Bottom Dead Centre

The position of the crankshaft when the piston is at its lowest position in the cylinder.

Bounce

Vehicle body suspension movement when hitting bumps.

Bounce Test

A manual test of suspension dampers (shock absorbers) by pushing down on the suspension and observing the oscillations when released.

Bounce-back

Movement of an electric window as it hits an obstruction - and bounces back (opens again).

Boundary lubrication

This form of lubrication is essentially a breakdown of hydrodynamic action. At high loads or low speeds, the pressure of the oil film cannot prevent metal-to-metal contact. So the opposing surfaces partially ride on an oil film and partially rub together as surface high points come in contact. Lubrication is provided by lubricant decomposition products or surface-active additives which form a thin, soft, solid film on the metal surfaces and prevent metal-junction adhesion.

Bourdon Tube

A U shaped tube used to measure vacuum.

Box Sections

Parts of the vehicle body - chassis and structural members.

Boxer Engine

A horizontally opposed engine.

BP Sensor

A barometric pressure sensor.

BPS

Back pressure Sensor

BPT

Back Pressure Transducer

Brake

(1) Device to retard the motion of a vehicle or to prevent inadvertent movement when parked. (2) Dynamometer for measuring the power of an engine, originally a friction brake by which torque could be measured. Also brake dynamometer (informal).

Brake Accumulator

A pressure container fitted into pumped hydraulic systems to maintain a reserve of pressure if the pump fails. They also smooth out the pump pulses in the system.

Brake Adjuster

A mechanical device for taking up the free play in brake components. Can be either manually or automatically operated.

Brake Balance

The splitting of brake effort to each axle in relation to the optimum that the axle can provide.

Brake Band

A friction material lined strap around a epicyclic gear annulus. Operated by hydraulic pressure to hold the annulus for gear ratio selection.

Brake Booster

See brake servo.

Brake Caliper

The fixed component of a disc brake holding the pistons that apply an inward force to press the brake pads onto the rotor.

Brake Cylinder

The wheel cylinders of hydraulic brakes in the brake unit.

Brake Drum

Rotating drum inside which brake shoes operate.

Brake Fade

Reduction of braking effort resulting from overheating of friction surfaces, or other transient effect.

Brake Fluid

A special liquid used in hydraulic brake systems. Always check data because some types should not be mixed.

Brake Horsepower (bhp)

A measure of the power output from an engine when measured with a dynamometer using a brake applied to the engine flywheel. The engine effort to overcome the braking force gives the bhp value.

Brake Lines

The hydraulic pipes and hoses of the brake system.

Brake Lining

The friction material attached to brake shoes and pads.

Brake Linkage

A general term to describe components that link different parts of the brake system together.

Brake Pad

A steel plate with a bonded friction lining used on disc brakes. Similar to the brake shoe of a drum brake.

Brake Rollers

Rollers used to drive the wheels of a vehicle for brake testing purposes.

Brake Servo

A mechanism (vacuum or hydraulic) that increases the braking effort applied by the driver.

Brake Shoes

Part of drum brake carrying linings.

Braking Effort

The force applied to the brakes.

Braking Thrust

Forces that are caused by braking.

Breakout Box

A terminal box for carrying out diagnostic tasks on electrical and electronic systems.

Bridge Rectifier

A type of rectifier using four or more diodes to give full wave rectification.

Bridging

A characteristic of undercoat performance that occurs when a scratch or surface imperfection is not completely filled, leaving a cavity underneath. It i caused by under-reducing the primer or using too fast a solvent and can lead to the appearance of sand scratches in the finished repair.

Bronzing

The formation of a metallic-appearing haze on a paint film.

Brush End Plate

A plate used to hold brushes in contact with a commutator.

Brushes

Pieces of carbon or metal ending in wires or strips. Contacts onto rotating slip-rings or generator/motor commutators.

BTDC

Before Top Dead Centre

BTDC - Before Top Dead Center

BTDC - Before Top Dead Centre.

BTDC - Before Top Dead centre

The position of the crankshaft before the piston has passed the top of the cylinder and is still on the way up.

Btu

British Thermal Units

Buffing

A technique used to polish an area to remove sanding marks or surface imperfections (see Polishing).

Buffing Compound

Soft paste containing various grades of fine abrasives suspended in a neutral medium, used to eliminate fine scratches and polish the topcoat.

Build

The amount of paint film deposited on a substrate (the depth or thickness of which is measured in microns).

Bulkhead

Substantial structural panel of vehicle body in front of passenger compartment. Also known as a firewall.

Bump Cap

A hard hat.

Bump Steering

Steering action that results from hitting a bump.

Bump Stop

A rubber spring that limits and dampens the movement of a spring to prevent excessive deflection and spring damage.

Buoyancy

The ability to float in liquid or in air.

Burrs

Term used to describe rough edges on metal components.

Bus

A motor vehicle which is constructed or adapted to carry more than eight seated passengers (see also Minibus).

Bush

Cylindrical sleeve forming a bearing surface for a shaft or pin.

Bushes (rubber)

A metal and rubber composite bearing that provide both a limited range of movement and insulation from road vibration.

Buss Bar

A conductor in a fuse box or other electrical distribution device.

Butyl

Synthetic rubber impervious to oxygen.

Butyl Acetate

A medium-evaporating solvent used in paint.

Bypass

A secondary route in a system that allows gas, liquid or electricity to flow outside of the main route.

Bypass Valve

In a lubrication system a valve that allows oil to bypass a filter.
C

C

Celsius

C Classification (SAE)

Engine oil suitable for diesel engines. The second letter in the classification denotes the quality and minimum conditions that the oil must meet.

C.F.P.P

Cold filter plugging point. Applies to diesel fuel with a cold weather additive."

C3I

Computer Controlled Coil Ignition

Cadence braking

An emergency braking procedure using rhythmic application and release of the brakes to strike a compromise between slowing down with locked wheels, so retaining the ability to steer.

Cadmium

A metal used in the manufacture of durable but expensive red and yellow pigments.

Calcium

A soft grey metallic element used a component in driers and pigments.

Calcium Carbonate

An extender pigment, also known as "whiting."

Calibrate

The act of making sure a piece of measuring equipment is accurate. Often this is done by checking it against equipment that is known to be good.

Calibrated

This means that a piece of measuring equipment is accurate. Often this is done by checking it against equipment that is known to be good.

Calibrated Aperture

An accurate size hole to control flow.

Calibrated Float

The float used in a hydrometer. It is designed to work accurately (calibrated) usually at 15 degrees Celsius.

Calibration Resistor

A variable resistance that is used to set the basic position of a circuit.

Caliper

In a disc brake system, the mechanism that brings brake pads to bear on the disc by a clamping or pinching action, similar to that of the jaws of a Vernier caliper.

Caliper Piston

A slave cylinder in a brake caliper.

CALPAK

Calibration Pack

Cam

(1) A shaped or profiled component that produces linear or angular motion or lift of a follower. Except in the steering box, most automotive cams are in the form of non-circular wheels which impart motion to the follower by their rotation. (2) A camshaft (informal). Misleading usage, as for instance twin cam to describe an engine with two camshafts.

Cam Belt

Belt, usually made of reinforced rubber, which drives the cam from the crank.

Cam Linkage

A cam shaped (egg shaped) part.

Cam Lobe

High point of a cam which operates components.

Cam Plate

A plate with one or more raised areas in the shape of a cam. Used in rotary diesel injection pumps to supply high pressure injection.

Cam Ring

A shaped ring with a cam shape.

Camber

(1) Convex arched curvature of a (usually horizontal) surface. (2) Average curvature of the chord wise section of an aerofoil. (3) Mildly arched profile of a road or pavement. (4) Inclination of the plane of a wheel to the vertical plane of symmetry of a vehicle. Camber is considered positive if the wheel leans out towards the top, and negative if it slopes inward.

Camshaft

Shaft on which suitably phased cams are mounted, as for example to operate intake and exhaust valves of an engine. In four-stroke engines the camshaft rotates at half crankshaft speed.

CAN

Controller Area Network. A protocol for a multiplexed system of control and communication on a vehicle.

CAN Bus

The actual circuit on which the CAN signal/message is transmitted. It is usually a pair of wires but fibre optics have been used.

CAN message

The information transmitted on a data bus from one node to another.

CANP

Canister Purge Solenoid Valve

Cap (Tire Valve)

Air Valve. Secondary air valve for an inflated tire.

Capacitance

An ability to store an electrical charge in two conductors separated by an insulator.

Capacitor

Electrical/electronic device consisting of two plates separated by an insulator. It is capable of holding a charge.

Capacity (engine)

Applied to the sum total of the swept volumes for all cylinders in an engine. Also known as 'total displacement'.

Carbon Black

A black pigment manufactured by collecting the carbon resulting from incomplete combustion of natural gas.

Carbon Monoxide (CO)

Polluting, odourless, toxic (poisonous) gas produced by incomplete combustion of fuel.

Carburetor

See Carburettor.

Carburettor

Device for Vaporizing liquid fuel and mixing it in appropriate proportions with a stream of air, prior to combustion in an engine.

Cardan Joint

A drive shaft universal joint consisting of two yokes and a cross bearing. Also Hooke's joint.

CAS

Crank Angle Sensor

Casting

A metal forming process where molten metal is poured or injected into a mould.

Castor

(1) Originally an undercarriage member with a vertical pivot axis behind which the wheel trailed, so that the wheel aligned itself to its direction of motion. (2) Steering geometry, parallel to the direction of travel, in which the steering pivot is inclined away from the vertical in order to give the effect of castor as described in 1. Also castor offset and castor trail. Small pivoting wheel attached to piece of furniture to facilitate movement.

Castor Angle

Angle in side elevation between the steering and vertical axis.

Catalyst

A substance that causes a chemical reaction when it is mixed with another substance.

Catalytic Converter

Uses platinum, palladium and rhodium to change pollutants in exhaust gases to harmless substances.

Catch Up

The process by which testing test data recorded while testing under Emergency Testing is subsequently entered via the VTS Device.

Cathode

A negative connection.

Cationic electrodeposition

One of the electro-coating (E-coat) methods in which the body is charged negatively and the paint positively. The cationic method is superior to the anionic method in terms of corrosion resistance. Frequently used for OEM primer application.

Caulking

Sealing used in joints to prevent the passage of fluid (commonly moisture) or gas.

Cavitation

The formation of cavities in a structure or of gas bubbles in a liquid, or of a vacuum or partial vacuum as between a body moving in a fluid and the fluid.

CC

Cubic Centimetres

CCA

Cold cranking amps (a rating for batteries)

CCMC

Comite des Constructeurs d'Automobile du Marche Commun. The European organisation that set standards for engine lubricants. This organisation has been replaced by ACEA (Association des Constructeurs Europeens d'Automobiles).

CD ROM

Compact Disk Read Only Memory. Stores up to 800Mb of data. The data is 'read only' which means that you cannot change or overwrite it.

CDI

Capacitor Discharge Ignition

CDI (Ignition)

Capacitor discharge ignition system that uses a capacitor to produce the high tension for arcing across the electrodes of the spark plug.

CEAB

Cold Engine Air Bleed

CECU

Central Electronic Control Unit

Cell

That part of a battery made from two dissimilar metals and an acid or alkali solution. A cell stores chemical energy for use later as electrical energy.

Cell Caps

Removable covers for a battery cell.

Center Bearings

See Centre Bearings.

Center of Gravity

See Centre of Gravity.

Centre Bearings

Bearings usually used to support a rotating shaft - at its centre. Many RWD propshafts have a centre bearing for example.

Centre Link

The centre track rod of a three-part steering system which connects the steering box drop arm to the idler and the two outer track rods.

Centre of Gravity

The point about which an object would balance in all directions. Also the point about which it can be said that gravity is acting on something.

Centre Point Steer

Steering geometry, parallel with the vehicle axis, in which wheel camber and steering swivel axes meet at the centre line of a steered wheel at ground level.

Centrifugal Force

The outward movement felt as a car turns a sharp corner.

Centrifugal Unit

Mechanical system using weights attached to a shaft. These move out against spring force as the shaft speed increases. Senses shaft speed for ignition advance and diesel pump speed.

CER

Cold Enrichment Rod

CESS

Cold Engine Sensor Switch

Cetane Number

Applies to diesel fuels as a measure of the delay in ignition after injection. A higher number indicates a shorter delay.

Cetane Rating

See cetane number.

CFI

Central Fuel Injection

CFI (Fuel Injection)

Usually centre point fuel injection system but sometimes used for continuous fuel injection.

cfm

Cubic Feet Per Minute

Chaffing

Used to describe the unintentional action of one component rubbing against another.

Chalking

The degradation of a paint film by gradual erosion of the binder, typically due to weathering. It is common in ageing red finishes and is characterized by a pinkish haze and loose pigment particles on the surface of the paint

Chamois

A soft suede leather formerly from the skin of the chamois antelope but now more often made from sheepskin.

Charcoal Canister

A part of a fuel evaporative (EVAP) system. The charcoal absorbs petrol vapour during fuel tank venting and returns the fuel to a reverse air flow and into the engine under specific conditions.

Charge Current

See charge rate.

Charging

Process of building up the level of charge in a battery or capacitor.

Charging Rate

The recommended rate of charge for a battery. Usually one tenth of the amps in the Amp hour rate for one and a half times the hours for a fully discharged battery.

Chassis

Structural lower part of a vehicle to which the running gear and body are attached. The true chassis is now evident only in larger vehicles.

Check Valve

A one way valve, using a plate or ball and spring, that permits fluid flow in one direction only. Used in hydraulic systems to retain a residual pressure.

Checking

A type of paint film defect in which cracks in the film begin at the surface and progress downward. The result is usually a straight v-shaped crack which is narrower at the bottom than the top.

Checksum

A checksum is a count of the number of bits in a transmission unit that is included with the unit so that the receiver can check to see whether the same number of bits arrived. If the counts match, then one can assume that the complete transmission was received.

Chemical Bond

A reaction between atoms that causes a force such as to create a bond.

Chemical Cartridge Respirator

A respirator which uses a cartridge containing various chemical substances to purify inhaled air of certain gases and vapours.

Chemical Staining

Spotty discolouration of the topcoat sometimes caused by environmental conditions (acid rain, tree sap, etc.) It can also be caused by improper activation of body filler which leads to staining in the subsequent layers of topcoat.

Chemical Treatment

A process that uses chemical to bring about a change in something.

Chip

Description of an integrated circuit where the circuit is built on a silicon chip.

Chipping

Small flakes of a finish losing adhesion from the substrate. Usually caused by the impact of stones or hard objects.

Choke

A restriction in a carburettor. The term is used to describe either the venturi as in single or twin choke carburettor, or for the cold start device.

Choke Flap

The butterfly type valve that restricts the flow of air.

Chopper Module

An electronic circuit or unit that switches a supply on and off rapidly.

Chroma

The level of saturation or intensity and richness of a colour. De-saturated or "dirty" colours have less chroma; saturated or "clean" colours have more chroma.

Chromate

A chemical compound used as a component in primers to provide corrosion protection to metal.

Chromate Rinse

Newly manufactured vehicle bodies are completely immersed in a chromic acid solution after zinc or iron phosphating to passivate the metal at the base of cracks and pinholes in the phosphate. Chromate rinsing, as used in modern mass-production paint preparation, will greatly increase corrosion resistance.

CID

cylinder identification sensor

Circuit

A complete conducting path.

Circuit Board

A board used to construct an electronic circuit.

Circuit Breaker

A switch to turn off the current flow in a circuit. Can be manually or automatically operated.

Circuit diagram

A diagram using symbols for electrical and electronic components that represents a real circuit.

Circumference

The boundary line of a circle.

CIS

Continuous Injection System

CKP

Crankshaft Position Sensor

CKP Sensor

Abbreviation for the crankshaft position sensor.

Clamp Plate

A simple plate to hold another item securely.

Clarify

To make clear.

Clays

Clay is a naturally occurring material composed primarily of fine-grained minerals. It is used in some cases to act as a very fine abrasive for improving paintwork.

Cleaner

Material used to remove dirt and other impurities from a substrate prior to painting.

Clear Coat

The transparent, non-pigmented top coat that is applied over a coloured base coat paint. Most modern cars have factory-applied clear coat paints. Clear coat paint increases paint durability, gloss, and resistance to harmful environmental effects such as ultra-violet radiation.

Clearance

A gap between two components.

Clearance Fit

The relationship between the dimensions of two components where one fits inside the other. In this instance the fit is one where the inner dimension of the outer component is greater than the outer dimension of the inner component.

Clearance Size

A drilling size slightly larger than the nominal size of a thread.

Clearance Volume

The space above a piston at top dead centre in a cylinder. Includes the combustion chamber and any other volume formed by the thickness of gaskets, etc.

Clipboard

A temporary area used to store copied information.

Clock spring

These are generally made of rectangular section material, flat strip, with round edges. They are general used as brush springs in D.C. motors. Also known as spiral springs

Clogging

Condition where abrasive paper becomes clogged by the abraded surface coating.

Closed Circuit

Applied to an electrical circuit when the switch is 'on' or the circuit is continuous.

Closed Loop

A system where a change in the output causes a changed input which in turn changes the output and so on...

Closed Loop System

Electronically controlled system, which adjusts settings by feedback from sensor signals that are monitoring the performance of actuators in the system and comparison with the pre-programmed map.

Clouding

The formation or presence of a haze in a liquid such as a paint film.

Clutch

A device to allow drive to be connected and disconnected. In a starter motor a clutch is used to only allow drive to pass one way - starter to engine, NOT engine to starter.

Clutch (Transmission)

Disengages / Engages drive from the engine.

Clutch Fork

See Release Fork.

Clutch Linkage

Mechanism to connect the pedal to the clutch release bearing. May be cable, electrically or hydraulically operated.

Clutch Pack

A set of friction plates and pressure plates in a multi-plate clutch.

Clutch Plate

The friction plate used as part of a clutch.

CMP

Camshaft Position Sensor

CMP Sensor

Abbreviation for the camshaft position sensor.

CO

Carbon Monoxide

CO2

Carbon Dioxide

Coach

A motor vehicle which is constructed or adapted t carry more than 16 seated passengers, with a DGW of more than 7,500kg and a maximum speed in excess of 60mph.

Coaching

Coaching is a method of directing, instructing and training a person or group of people, with the aim to achieve some goal or develop specific skills.

Coalescence

The fusing or flowing together of liquid particles. The term is frequently applied to waterborne coatings, which require coalescence to form a continuous film.

Coasting

Driving on very light throttle at a constant speed.

Coating

The act of applying paint or the actual film left on the substrate by an applied paint. A single coat may be produced by two passes of a spray gun, one overlapping the other in half steps. A double coat is two single coats with little or no flash-off time between them.

Cobwebbing

The tendency of sprayed paint to form strings or strands rather than droplets as it leaves the gun. May be caused by too fast or improper solvent, paint too thick or air pressure too low.

Coefficient of Friction

A value between 0 and 1 that indicates the ability of two materials to grip each other when sliding or rolling in contact with other.

Coil (Ignition)

An electrical transformer that increases the battery voltage to a high tension capable of arcing across the gap of spark plug electrodes.

Coil Spring

A spring that consists of a single length of bar wound into a helix (coil).

Cold Cranking Rating

Applies to a battery's ability to provide a minimum current for a minimum time for starting a cold engine.

Cold Start Enrichment

An increase in the amount of petrol mixed with the air under cold starting conditions.

Cold Start Valve

An extra valve used only when starting from cold.

Cold Starting

Cranking the engine so that it will start and run under cold conditions.

Cold-Cracking

Cracking of a paint film resulting from a sudden drop in temperature, or repeated cycling from high to low to high temperatures.

Cold-start Valve

An extra valve used only when starting from cold.

Collector

Terminal of a transistor that becomes conductive to the emitter when the base is energised.

Collet

Small half-round and tapered components used to fix a valve stem to its cap.

Colour

The visual appearance of an object that can be described in terms of hue, value, and chroma. Colours are seen differently by different people and under different lighting conditions.

Colour Coat

The single-stage or basecoat that provides the visible colour of a coating system.

Colour Match

Achieved when the applied colour duplicates all aspects of the original colour's appearance in terms of hue, value, and chroma.

Colour Retention

The ability of a paint to maintain colour under exposure to light, heat, moisture or other conditions of use.

Colour Sanding

The sanding of a cured or dried paint film to prepare it for polishing or recoating.

Combustion

The burning of fuel in air.

Combustion Chamber

Area above the piston when it is at TDC where the combustion takes place.

Combustion Knock

Advanced or quick detonation of fuel in a cylinder where the resultant pressure rise causes a shock wave through the piston, crankshaft and engine block.

Combustion Stroke

The third stroke of the four stroke cycle when the fuel is burnt to produce heat energy, expansion of the air/fuel charge and power on top of the piston. Also known as the power stroke.

Communication

This is a process of transferring information from one entity to another. An exchange of thoughts and information if human.

Commutator

Rotating contacts for electrical windings on a generator or motor armature.

Compensating

A strategy that involves adjusting something up or down to more closely approximate the required or ideal value.

Compensator

Provides equal force to mechanically braked wheels.

Compliance Coating

A coating whose volatile organic compound (VOC) content does not exceed that allowed by regulations. Compliance coatings may be waterborne, low solvent, or powder.

Composite Materials

Material made up of constituents that remain recognisable.

Compound

Place where cars are taken when they die, or dogs when they get lost...A chemical where the two or more elements they contain combine at the molecular level - salt for example is a compound of sodium and chlorine (sodium chloride).

Compound Gear Train

Two or more pairs of gears.

Compounding

The use of an abrasive material, either by hand or machine, to smooth and enhance the gloss of the applied topcoat.

Compression

The reduction in volume of a gas when it is squashed. The gas pressure increases and the temperature rises.

Compression Ignition (CI)

Fuel ignited by heated air (diesel).

Compression Ratio

The ratio between the TOTAL volume of a cylinder (swept volume plus clearance volume) and the CLEARANCE volume (volume above the piston at TDC - the combustion chamber).

Compression Ring

A piston ring that helps to contain combustion pressure.

Compression Spring

A spring that is designed to provide force when compressed.

Compression Stroke

The second stroke of the four stroke cycle when air or the fuel/air mixture is compressed. Compression is necessary for clean and efficient combustion of the fuel.

Compressor

Electrically or mechanically driven pump used to increase pressure of a gas or liquid.

Compressor Wheel

Part of a turbocharger that pumps extra air into the intake and therefore the engine.

Compulsory

Must be completed.

Computer Application

Programs such as Word, Excel and PowerPoint.

Computer Crash

An event that causes the computer to become inactive. This can often result in the loss of unsaved work.

Con Rod

Short for connecting rod, this joins the pistons to the crankshaft.

Concentric

A term that describes objects that revolve or are fitted around a common centre.

Concise

Expressing a lot but in few words.

Condenser

1. Part of an air conditioning system positioning in the outside air stream. It gives off heat to atmosphere as a refrigerant condenses. 2. Alternative name for a capacitor in an ignition system.

Condenser (A/C)

A heat exchanger in an air conditioning system that is similar to, and fitted in front of, the coolant radiator where it passes heat energy to the air stream passing through it. Operates by condensation of the refrigerant from gas to liquid by pressure and heat loss.

Condenser (Ignition)

An electrical capacitor that is used in a contact breaker ignition system.

Conduction

Transfer of electrical or heat energy along material.

Conductor

A material that allows free movement of electricity or heat through it.

Conductor Foil

General term to describe a type of 'flat' wiring harness.

Cone Clutch

A simple clutch shaped like a cone. Used as part of a synchromesh mechanism.

Cone Pulley

A pulley shaped like a cone such as to allow different ratios to be set by the position of a drive belt.

Confidential Information

Information that is private and should be protected.

Connecting Rod

The engine component that joins the piston to the crankshaft.

Constant Velocity Joint

A drive shaft joint that transmits drive through an angle without changes in speed.

Construction and Use

The UK Construction and Use Regulations that cover the legal requirements on manufacturers and users of road vehicles.

Constructive feedback

A way of giving feedback to somebody so that they feel valued and that they can improve what they did based on your comments.

Consumption

The rate at which a vehicle uses fuel.

Contact Breakers

Mechanical spring-loaded switch located in the distributor of an ignition system and actuated by a rotating cam. It makes or breaks the ignition circuit to control the coil output and delivery of a spark to the spark plug.

Contaminant

Something which contaminates; an impurity; foreign matter

Contaminants

Any polish, wax, tree sap, tar, oil, etc., that would damage the paint film or spoil the adhesion of a new paint film.

Continuity

The condition of an electrical circuit when a current will flow.

Continuous Injection

Injectors that inject or 'squirt' all the time.

Continuous Injection Systems

Injection systems where the supply to the inlets is active all the time but may only 'spray' on the intake stroke due to the lower pressure.

Contouring

(see Mapping)

Contract

Agreement between parties enforceable in law.

Contraction

A decrease in size. For example, when a metal rod is cooled it decreases in length and diameter. Opposite of expansion.

Control Flap

A flap that is used to control something! Air temperature for example.

Control Plunger

Part of fuel injection system. Regulates fuel delivery against air flow.

Control Pump

A pump that provides a set pressure.

Convection

Travel of heat by movement in heated fluids due to a reduction in density and consequent rise of the hotter material.

Conversion Coating

Conversion coatings are used on metal parts (such as vehicle bodies) to be painted. They are acidic chemical products used before paint to convert the metal substrate to an iron or zinc phosphate surface. The chemical reaction modifies the metal surface to enhance paint adhesion and corrosion protection

Conversion Factor

Used to make it easier when converting from one form of ‘measurement' to another.

Conversions

To change one expression to another. For example, expressing miles in kilometres.

Converter

An additive used to provide a chemical reaction to cure paint. Also used with some primers to convert them to 'non-sanding' versions, by changing their properties and making them suitable for wet-on-wet procedures.

Coolant

Liquid made up of water, anti-freeze and inhibitors used to cool an engine in a sealed but circulated liquid system.

COP

Coil on plug, where a different ignition coil is used for each spark plug on an engine. Also known as direct ignition.

Copper

A difficult metal substrate to paint. Also used in the manufacture of special decorative pigments and synthetic driers.

Core Plug

A steel plate fitted into a cylinder block or cylinder head casting after the casting sand has been removed in order to produce a fully sealed component.

Corrosion

The decomposition of a metal in contact with its environment - a chemical reaction of oxygen and moisture or corrosive materials on a metal surface. Also called oxidation or rusting (on ferrous metals).

Corrosive

An acid or other chemical that will chemically react or attack another material.

COSHH

The Control of Substances Hazardous to Health Regulations 2002 is a United Kingdom Statutory Instrument that stipulates general requirements on employers to protect employees and other persons from the hazards of substances used at work by risk assessment, control of exposure

Cost of production

The actual cost to the manufacturer of producing a vehicle (it does not include mark-up).

Cotter Pin

Tapered pin used to hold shafts into housings. May also be used to describe a split pin.

Counter Gear

See countershaft assembly.

Counter Shaft

An alternative term used to describe the layshaft in a manual gearbox. The shaft in a manual gearbox carrying the gear cluster and meshing with the constant mesh gears.

Countershaft

An alternative term used to describe the layshaft in a manual gearbox. The shaft in a manual gearbox carrying the gear cluster and meshing with the constant mesh gears.

Countersteer

Steering force that acts such as to prevent the wheels moving off their intended line.

Couple

A pair of equal parallel forces that are opposite in direction. The effect of a couple is to produce or prevent the turning of a body.

Coupling Point

The point or speed at which a torque converter takes up drive.

Courtesy Lights

Lights for the vehicle occupants to use.

Coverage

The amount of area a volume of paint will cover at a certain thickness. Theoretical coverage is described as the number of square metres a coating will cover at 1 mm film thickness.

Cowling

General term used to describe a cover.

CPI

See single point injection.

CPS

Crankshaft position and speed sensor.

CPU

Central processing unit. This relates to the main component in an ECU or computer.

Cracking

Splitting of a paint film. Cracking usually appears as straight lines which penetrate the entire film thickness and can be caused by over-baking or by application of excessive film builds.

Crank

A term used to describe turning the engine by the starter motor.

Crankcase

The part of the engine that houses the crankshaft and the bearings in which it runs. It can be either a separate part or be integral with the engine block.

Crankcase Ventilation

Usually a positive crankcase ventilation (PCV) system that allows any crankcase pressure and oil vapour to be passed into the combustion chamber so that it does not escape into the atmosphere as a pollutant. Early crankcase ventilation consisted of an open vent or breather tube that allowed crankcase gases to be passed out below the vehicle.

Cranked

Description of making the engine rotate on the starter motor.

Cranking

The process of turning over an engine using a starter motor (or a handle on earlier models!).

Crankshaft

Major rotary component of engine that converts piston movement into rotary movement.

Crankshaft Damper

Usually part of the front pulley. A rubber mounted mass reduced torsional vibration.

Crankshaft Oil Seal

Usually radial lip type seals at the front and rear of the crankshaft.

Crankshaft Pulley

Main drive pulley on the end of the crankshaft.

Crankshaft Shell

See Shell Bearings.

Crankshaft Web

Counterbalance weights that are opposite the big end bearing journals.

Cratering (silicone cratering, see

'Fish Eyes')">Small round depressions in a paint film which may or may not expose the underlying surface. Frequently caused by contamination of the substrate by wax, oils, etc.

Crawling

The tendency of a wet paint film to recede from certain areas of a painted surface. Often caused by the presence of contaminants on the surface.

Crazing

The formation of surface cracks, often as a fine network, which do not penetrate to the underlying surface of a paint film. Crazing is sometimes caused by the softening effect of solvents from excessive paint coats as in cellulose or acrylic lacquer repair operations.

CRC

A cyclic redundancy check is a method of checking for errors in data that has been transmitted on a communications link.

Crescent Pump

A positive displacement pump made from one externally and one internally toothed gear rotating eccentrically in a housing. Inside the housing, and in the space formed where the teeth are out of mesh, is a crescent shaped block. This divides the gear teeth to create the pumping and carrying chambers of the pump.

Crimp

Act of squeezing a connection such as a terminal onto a wire.

Crimped Joint

Termination of cables by squashing tabs on the terminal around the cable.

Crimping

The process of compressing materials to make a join. Usually refers to squeezing a terminal to secure it to a wire.

Crocodile Clip

Hand operated clip that, like a crocodile, bites under spring pressure to make a contact. Also alligator clip.

Cross Member

A chassis or support member that runs across a vehicle frame or chassis.

Cross-Coat (double-header)

A method of paint application often used with high solids paint. The technique involves a side-to-side application followed by a top-to-bottom application with very little flash-off time. Also used by some refinishers when they apply 'drop coats' in more than one direction to eliminate striping in metallic and pearlescent finishes.

Cross-draft Booth

A spray booth in which air movement is horizontal from end to end, i.e. fresh (may be heated) air enters at the front of the booth and is extracted at the rear Not considered to be as efficient as downdraught extraction

Cross-pin (Hooke's) Joint

Type of universal joint with a cross pin and two yokes.

Cross-ply

Form of tyre construction in which the casing plies are laid diagonally so that each ply lies at an included angle, usually of more than 40 degrees, to the adjacent ply.

Cross-section

The area exposed if a cut were to be made through the centre of an object.

Cross-shafts

General term used to describe shafts which are fitted across units rather than along or axially.

Crown Wheel

Bevel gear wheel in which the teeth are set around the periphery, giving the wheel the appearance of a crown. The larger wheel of the crown wheel and pinion bevel pair.

Cruise Control

A system that keeps the vehicle at a set speed.

Cruising

Driving at a constant speed under light throttle conditions.

Crumple Zone

Safety feature of vehicle body, absorbs impacts.

Crystalline

The arrangement or bonding of atoms in solid materials which form during cooling to give regular structural patterns.

Crystalline Structure

The arrangement or bonding of atoms in solid materials which form during cooling to give regular structural patterns.

CSSA

Cold Start Spark Advance

CSSH

Cold Start Spark Hold

CT

Closed throttle.

CTS

Coolant Temperature Sensor

CTS Sensor

Abbreviation for the engine coolant temperature sensor or switch.

CTVS

Choke Thermal Vacuum Switch

CTX Transmission

Constantly Variable TransaXle.

Cup Seal

A hydraulic seal with a lip that contains pressure against the lip but will allow a flow in the opposite direction. Used in the cylinders of brake systems.

Curb Idle

Rotational speed of an engine on no-load and minimum throttle setting. Also tick over and idle.

Cure

The process, usually a chemical change, by which paint is converted from the liquid to the solid state.

Cured Paint

Paints that have completed the curing process. Cured paints include all factory-applied paints and refinish paints that have air-dried for more than 30 days. Wax application is recommended only for fully cured paints.

Current

Movement of electrically charged particles. Current flow is measured in Amperes.

Current Regulator

An electrical or electronic device used in generator circuits to control the output current.

Current Relay

A device that usually incorporates a reed switch. It is activated by current flow through a series winding.

Custom Painting

Unique painting, frequently with special effects or designs, normally designed by owner of vehicle and/or the specialist who will be painting the vehicle.

Cut

Refers to both the dissolving of solid material in a solvent and the reducing of the viscosity of a liquid by the addition of a thinner.

Cut-off

Process where fuel supply can be stopped, for example when a vehicle is coasting down.

Cutoff

See Cut-off.

CV (Constant Velocity) Joint

A drive shaft joint that transmits drive through an angle without changes in speed.

CV Joint

A drive shaft joint that transmits drive through an angle without changes in speed.

CVR

Control Vacuum Regulator

CVT (Transmission)

Constantly variable transmission that uses two conical drums and a drive belt between them. The effective diameter of each drum is varied hydraulically in order to change the drive ratio.

Cylinder (Master)

(1) Primary source of pressure in a hydraulic system such as brake or clutch system, containing the piston by which pressure is applied and connected to a source of hydraulic fluid. (2) Primary unit for dispensing hydraulic fluid under pressure in a hydraulic system.

Cylinder (Slave)

Cylinder and piston that, under hydraulic or pneumatic pressure from a master cylinder, actuates mechanical components. For example, the brakes or a clutch.

Cylinder Balance

A test carried out with diagnostic equipment to make sure each cylinder of the engine is working to its full potential.

Cylinder Block

The part of an engine containing the cylinders. The cylinder block may also incorporate the water cooling jackets and provisions for the valve gear.

Cylinder Bore

The diameter of the cylinder.

Cylinder Charging

Process of filling a cylinder during the induction stroke.

Cylinder Head

Encloses the top of the cylinder block.

Cylinders

Cylindrical or tubular chambers in which the pistons of a reciprocating engine or pump are fitted. They are contained in the cylinder block.
D

DA (Dual Action)

Refers to a power sander used for flatting substrates.

DA (Dual Action) Sander

A machine used for random orbital sanding and buffing. The pad of a DA sander travels in a randomized orbital pattern, rather than taking a simple circular path. DA sanders minimize the swirl marks that commonly result from rotary sanding and greatly reduce the time necessary to produce feather-edges.

Dampener

A device to reduce oscillations or vibrations. A kind of damper.

Damper

Component that reduces the oscillations of a spring in a suspension system. A device that smoothes out fluctuations.

Damping

The reduction of oscillations or smoothing out of fluctuations.

Damping Chamber

An air space in which a damper flap moves that acts to reduce oscillations.

Darlington Circuit

Two transistors connected so that the first switches the second. Used to switch high currents.

Dashpot

A damper used on some variable venturi carburettors.

Data

In computer science, data is anything in a form suitable for use with a computer. Data is often distinguished from programs. A program is a set of instructions that detail a task for the computer to perform. In this sense, data is thus everything that is not program code.

Data Link

General term for a connection to a scanner or similar diagnostic tool.

Data rate

The actual speed at which data is transmitted.

Databank link

A connection to an electronic source of data.

dB

Decibels

DC

Direct Current

DC Brushless Motor

A DC Brushless Motor uses a permanent magnet external rotor, three phases of driving coils, one or more Hall effect devices to sense the position of the rotor, and the associated drive electronics.

DC Direct Current

An electrical current that flows in one direction only. Conventionally from the positive pole to the negative pole.

DC-DC converter

This is an electronic circuit which converts a source of direct current (DC) from one voltage level to another. It actually converts DC to AC to a different voltage AC and then back to DC!

de Dion suspension

A de Dion suspension uses universal joints at both the wheel hubs and differential, and uses a solid tubular beam to hold the opposite wheels in parallel. Unlike an anti-roll bar, a de Dion tube is not directly connected to the chassis nor is it intended to flex.

De-energised

Switched off - usually refers to a coil or relay.

De-ionised

Used to describe pure, neutral water used for topping up batteries.

Dead Axle

A non-driving axle. Supports the vehicle and carries freely rotating wheels.

Dead centre

Top or bottom piston positions in the cylinder when the crankshaft is at 0° or 180° of rotation.

Deceleration

Opposite of acceleration. Reducing velocity or speed. Slowing down.

Decelerometer

Brake Meter for recording rate of deceleration during braking for test purposes.

Decimal

A number system that uses a base of 10.

Decimal Place

The position of numbers after (to the right of) the decimal point.

Deck (Block)

The top of the engine block forming the mating face for the cylinder head.

Dedicated Test Equipment

Equipment made to work specifically with one system or one manufacturer's vehicle range.

Deep Socket

Same as a normal socket but longer to allow it to be used on a component such as a spark plug.

Defamatory

Untrue and harmful information.

DEFI

Digital Electronic Fuel Injection

Deflection

Applied to springs to indicate the amount of movement away from the original position.

Degradation

The gradual or rapid disintegration of a paint film, normally due to weathering. May be simply fading/loss of gloss or can lead to total paint film breakdown

Degreasing

Cleaning a bare or previously painted substrate by removing greases, oils, and other surface contaminants.

Degrees of Advance

Refers to crankshaft rotation degrees as linked to ignition timing.

Delamination

The loss of adhesion between two or more layers of paint, causing material to separate from the painted surface or substrate.

Delta Wound Stator

An alternator stator winding with the three-phase coils connected at the ends in order to give a large current output.

Density

An expression of the mass of a substance for a given volume, e.g. water has a density of 1kg per litre

Desiccant Bag

Chemical used to absorb moisture. Often used in AC systems to remove moisture from the refrigerant.

Detailing

Careful, in-depth cleaning and polishing of a vehicle's surface finish and/or interior surfaces.

Detent

A position holding device consisting of a spring and locking piece that locates in a groove. A locating device for holding sliding gears in mesh in a manual gearbox.

Detergent

A material intended to assist cleaning. The term is sometimes used to differentiate between soap and other surfactants used for cleaning.

Detonation

Ignition of fuel in an engine that is too early or too rapid. Produces a knocking or pinking sound.

DFS

Deceleration Fuel Shutoff

DGW

Design Gross Weight – i.e. the maximum gross weight that the vehicle was designed to operate at by the manufacturer. This is normally found on the manufacturer’s plate fixed to the vehicle, or in the case of older or heavier vehicles by a ‘Ministry Plate’. Such plates are not required on all vehicles.

DI

Direct injection of fuel, usually diesel, into the combustion chamber.

Diacetone Alcohol

A slow-evaporating solvent for paints.

Diagnostics

The process of determining the fault in a system based on observed or measures symptoms.

Dial Gauge

A gauge used to indicate lateral movement of a component, on a clock (dial) type display.

Dial Test Indicator

A gauge used to indicate lateral movement of a component, on a clock (dial) type display.

Diameter

The line that goes through the centre of the circle.

Diaphragm

Flexible disc or membrane which deflects under pneumatic or hydraulic pressure and, in so doing, imparts linear motion to a centrally-located rod or other form of mechanical actuator, as in an air brake or carburettor.

Diaphragm Spring

Dished clutch spring applying clamping force and disengagement linkage.

Dictionary

A book containing a list of words in alphabetical order. Each word has information given about it (i.e., the definition).

Die

Tool used to cut an external thread.

Dielectric

Used in a capacitor as an insulator between the two conductive plates.

Diesel

Heavy fuel oil for diesel engines. Compression ignition engine.

Diesel 'Knock'

Engine noise produced by very rapid rise in cylinder pressure following injection and ignition of the fuel in a diesel engine.

Dieseling

A condition in a petrol engine when it continues to run after the ignition has been turned off. Also known as running on or run on and usually occurs in a very hot carburettor engine where the fuel cannot be fully shut off.

Differential

Relating to or using a difference. Operating on differences in pressure. Bevel gear set that allows two wheels to rotate at different speeds.

Differential Pressure Valve

A valve that sets its position depending on the difference between two pressures, for example, two fuel pressures or fuel pressure and manifold pressure.

Differential Pressure Valves

Valves that operate under the control of TWO external pressures or the difference (differential) between them.

Digilal Converters

See Digital Converter.

Digit

A number.

Digital

A signal current with either an 'on' or 'off' voltage. Digital instruments which show a numerical value.

Digital Converters

Electronic devices that convert analogue signals to digital or digital signals to analogue.

Diluent

A liquid which increases the capacity of a solvent for the binder. Diluents cannot dissolve the binder themselves. They are usually used to control viscosity or flash-off times.

Dim-dip relay

A switching relay that results in a resistor being connected in series with dipped lights when ignition and sidelights are switched on. This safety feature as used on some vehicles – but not all.

Diode

An electronic one way valve with polarity bias manufactured from a semiconductor material.

Diode Pack

A collection of diodes that act as a rectifier. A minimum of six diodes in the pack are needed for a three phase alternator.

Dip Switch

A switch used to select main beam or dipped beam headlights. Sometimes called a dimmer switch.

Dipped Beam

The lower of the two headlamp beams, dipped to avoid blinding the drivers of oncoming vehicles.

Dipping

To apply paint to an article by immersing it in a container of the paint and then withdrawing the article and allowing the excess paint to drain from the part. Particularly useful for small parts, such as nuts, bolts, brackets, etc.

Dipstick

A stick used to dip in a fluid and check its level!

Direct Injection

Diesel engine design where fuel is injected directly into the cylinder.

Dirt Nibs

Small specks of foreign material in a dried paint film. They can be usually be removed by careful sanding and polishing.

DIS

Distributorless ignition system that uses an ignition coil or coils directly connected to the spark plugs. The ignition is triggered by the ignition module on signals from the ECM (Engine control module).

Disc Brake

Brake in which external friction pads are brought to bear on the faces of a rotor or disc, usually by the clamping action of a caliper.

Disc Sander

Power sanding tool used for grinding, sanding, and rough polishing of repaired metal areas.

Discard Dimension

The lowest safe value for a component before it needs to be replaced. Used for brake components such as drums and rotors.

Discharge Time

Refers usually to how long a capacitor will take to release all its stored energy. It can be calculated by multiplying the capacitance by resistance and by five (t = 5CR).

Discoloration

Change in colour of paint due to chalking, dirt collection, fading, darkening or tonal changes.

Discriminatory

Unfair or unequal treatment of a person due to their age, sex, disability, race, religion etc.

Disengagement

The act of removing a connection between two gears of through a clutch.

Disk Drives

The primary data storage device used by computers. It stores and retrieves data.

Dispersion Coatings

A type of paint in which the binder molecules are present as colloidal particles. Characterized by a higher percent sprayable solids than is possible with solution-bases paints.

Displacement

The swept volume of a cylinder between the top and bottom positions of the top of a piston.

Displacer Unit

A hydraulic suspension component that contains gas under pressure and a fluid.

Dissolution

Metallic particles from the basecoat surface in the clearcoat. If severe, the effect can alter the tone and exaggerate the metallic appearance.

Distilled

Purified by evaporation and condensation.

Distilling

Distillation is a method of separating mixtures based on differences in their boiling points in a liquid mixture.

Distinctness of Image

A measurement of the accuracy of a reflection in a paint film, which assists the painter in determining the quality of the surface gloss.

Distributor

A component in the ignition system that houses the primary circuit switching device and the secondary circuit distribution components.

Diverter Valve

Used on air injection systems to control the air feed according to the engine running conditions. Also known as a 'dump valve'.

Divider

A digital circuit that, for example, reacts to only every second input hence dividing it in two.

DLC

Data link connector for connecting a diagnostic tool to a vehicle's electronic systems.

Dog Clutch

Pegs or similar used to transfer drive rotation from one component to another.

Dog Drives

Pegs or similar used to transfer drive rotation from one component to another.

DOHC

Dual overhead camshaft. Sometimes double overhead camshaft.

Donut Coupling

A rubber universal joint shaped like a donut.

Double-Cardan Universal Joint

Two Hooke's or Cardan type universal joints close coupled to increase the effective angle of turn before inducing vibration.

Double-declutch

A technique that was necessary before the use of synchromesh mechanisms. During a gear change the clutch is lifted as the gear mechanism moves to neutral, the engine is revved (if changing down), the clutch is now depressed and the new gear selected.

Dowel

A locating pin between two mating components. Can be solid or hollow.

Down Draft

A carburettor where the choke tube (venturi) is fitted vertically.

Downdraft Booth

A spray booth in which the air movement is from the ceiling (input air) through the floor (extracted air).

Downshift Valve

Automatic transmission valve to give a downshift under specific drive conditions.

DPF

Diesel Particulate Filter

Drag Link

Steering linkage between the steering box drop arm (Pitman arm) and the drag arm on the steering swivel.

Drain Plug

Removable plug used to let fluid out (engine oil for example).

Drain Tap

A simple valve used to allow a fluid to be removed.

Drain Tube

A tube used to, for example, remove moisture from an air conditioning evaporator.

Drier

A chemical which, when added to an enamel, paint, varnish, or oil, hastens the drying or hardening of the film through evaporation.

Drive Axle

An axle that transmits a drive to the wheels. Also known as a live axle.

Drive Belt

Traditionally called the fan belt. A Vee or multi-vee belt to take drive from the engine to auxiliary components such as an alternator or water pump.

Drive Flange

A flange that is used to transmit drive from one component to another. The flange on the end of a propshaft is a good example.

Drive Gear

A toothed wheel to pass drive to another toothed wheel.

Drive Joints

General term used to describe any joint in a drive system such as a CV or universal joint.

Drive Line

Rotary shafts carrying drive to the wheels.

Drive Motor

A motor that supplies a driving force. Term usually refers to an electric motor.

Drive Pinion

A small gear that drives another gear.

Drive Plate

A plate that takes the place of the flywheel on an engine such as to transfer drive to a torque converter.

Drive Pulleys

Pulleys that transfer drive from one shaft to another.

Drive Ratios

Ratio between gears. For example 2:1 or 1.3:1.

Drive Shafts

Open shafts carrying the drive from the final drive to the driven wheels.

Driveline

Transmission components in the line between the engine and wheels.

Driveline Wind-up

Description of how a vehicle in four-wheel drive (with no centre differential) can build up spring tension in its transmission components. This is because the front wheels may rotate at a slightly different speed to the rear wheels.

Driven Plane

The plane (like a flat sheet) through which the drive operates.

Driven Plate

The clutch disc that is driven by the pressure plate.

Driveshafts

Open shafts carrying the drive from the final drive to the driven wheels.

Driving Beam

The upper of the two headlamp beams. Also main beam and upper beam.

Driving Thrust

Forces generated by the engine and transmission.

Drop Arm

The output arm on a steering gearbox. Also known as a Pitman arm.

Drop-Coat (Finesse coat)

A paint application method recommended on many Technical Data Sheets to eliminate patchy finishes in metallic and pearlescent basecoats. The atomising air pressure is reduced and the gun is held further from the surface. Providing the spray gun is then moved across the surface at a uniform speed, angle and distance, this technique should result in better orientation of the metallic and mica particles.

Dropping Resistors

Resistors used to reduce voltage to a component.

Drum Brake

Brake in which friction blocks or brake shoes lined with friction material are brought to bear on the periphery of a drum or cylinder. In most vehicle applications the shoes are brought into contact with the inner periphery of the drum.

Dry Clutch

A friction clutch that runs in an open housing. As distinct from a wet clutch that runs in an oil bath.

Dry Coat

A paint having a very low solvent content which produces a gritty film appearance.

Dry Film Thickness

The resultant film thickness of a coating after it has reached its final state of drying or curing. Measured in microns.

Dry Liner/Dry Sleeve

(US: dry sleeve) Hard metal engine cylinder liner or insert that is not exposed to contact with cooling water.

Dry Sanding

A method of abrading the surface by hand or machine without the aid of any water or other lubricant.

Dry Spray

Sprayed paint which loses so much solvent in the air that it becomes too dry to flow out over the surface. This normally occurs when the chosen thinners is too fast for the atmospheric or application conditions.

Dry Sump (Oil Pan)

An engine lubrication system where the reservoir of lubricating oil is held in an oil tank. The sump (oil pan) below the engine is scavenged with a separate pump for return to the oil tank. As distinct from a wet sump (oil pan) where the reservoir of lubricating oil is kept in an oil pan below the engine.

Drying

The change from a liquid to a solid which takes place after a paint is deposited on a surface. This involves both the evaporation of the solvents and any chemical changes that may occur.

Drying Oil

A liquid that will change to a solid under normal atmospheric conditions when spread out in a thin film.

DSG

Direct shift gearbox

DTC

Diagnostic Trouble Code

DTI

Dial Test Indicator.

Dual Bed Converter

A three way catalytic converter with one stage coated with platinum and palladium and the other with platinum and rhodium. Converts HC and CO to H and CO2 and NOX to N and O.

Dual Circuit Brake System

A brake system that has two independent hydraulic circuits so that one continues to act if the other fails. The split of dual circuits can be front and rear, diagonal, split front and one rear, and two complete circuits.

Dual mass flywheel

A dual-mass flywheel is used to isolate torsional crankshaft spikes created by diesel engines during the power stroke. Dual mass flywheels separate the mass of the flywheel between the engine and the transmission. This eliminates damage to the transmission components.

Dual Master Cylinder

A brake master cylinder with two separate chambers for a dual circuit hydraulic system.

Duct

Pipe, tube or trunking.

Ductility

The property of a material that allows it to be drawn into wires.

Ducting

Large pipes or similar. Usually refers to the air intake system components.

Dump Valve

See diverter valve.

Durability

Refers to the retention of gloss and performance properties in a paint film during prolonged use or exposure to sunlight and other atmospheric conditions.

Dust Contamination

Contamination due to visible dust particles of various sizes and forms which are embedded or form raised spots in the paint coating.

Dust-Free

Condition when a new paint film has dried sufficiently that it will no longer allow dust to penetrate and stick to the finish.

Duty Cycle

The percentage length of time that an actuator or solenoid is energised by an electronic control unit. Refers to the pulse width.

DVOM

Digital Volt Ohm Meter

Dwell Angle

The angle of distributor cam rotation when the contact breaker points are closed.

Dwell Meter

Measures the dwell angle.

Dwell Period

The angle of distributor cam rotation when the contact breaker points are closed. This term is used when the dwell angle is not a fixed value. Used for electronic ignition systems.

Dynamic

A term that indicates components that are in motion. The opposite of static.

Dynamo

Machine converting mechanical energy into electrical energy. DC.

Dynamometer

A measuring device for engine power output. A brake dynamometer measures the output at the engine flywheel to give the term brake horse power (bhp). A rolling road dynamometer measures the output at the vehicle wheels and is used for test and diagnostic purposes.
E

E.C. (E)

European Commission (Executive).

E.C.U

Electronic Control Unit."

E.C.U.

Electronic Control Unit.

E.M.F.(emf.)

Electro Motive Force.

E2PROM

Electrically Erasable Programmable Read Only Memory

EACV

Electronic Air Control Valve

Early Fuel Evaporation

Early fuel evaporation system using a heater element below a carburettor to heat the intake air and improve atomisation at cold engine speeds. Improves driveability and reduces harmful exhaust emissions.

Earth (Ground)

The electrical termination for components connected into a vehicle direct current earth return circuit. On mains electricity a safety route for an electrical short circuit used as a means of protecting people or electrical components from electrical overload.(Ground - US term)

Earth (Ground) Cable

The battery cable connecting the return side of a vehicle circuit to a terminal on the battery where a ground return circuit is used. (Ground - US term).

Earth Switching

Used to describe a circuit where the switch breaks the earth side of the circuit instead of the supply side.

Earth Switcing

See Earth Switching!

EATX

Electronically controlled automatic transmission.

EBCM

Electronic Brake Control Module

EBM

Electronic Body Module

ECA

Electronic Control Assembly

ECAT

Electronic Control of Automatic Transmission

Eccentric

Off centre. Usually refers to a rotating component with the operational part rotating about the central axis of the shaft. An example is a round cam offset from the shaft axis.

ECM

Engine control module. The electronic control module for engine management systems.

ECT

Engine coolant temperature sensor or sender.

ECU

Electronic Control Unit.

EDC

Electronic Diesel Control.

Edge-to-edge

Painting technique where full panels are sprayed without blending into masked off adjacent panelwork, or where panels are removed from the vehicle to be painted

EDIS

Electronic distributor or distributorless ignition system.

EDP

Explanation Demonstration Participation – a reminder of a good way to teach something practical to somebody.

EEC

Electronic engine control module.

EEPROM

Electronically Erasable Programmable Read Only Memory

EFC

Electronic Fuel Control

EFCA

Electronic Fuel Control Assembly

EFE

Early fuel evaporation system using a heater element below a carburettor to heat the intake air and improve atomisation at cold engine speeds. Improves driveability and reduces harmful exhaust emissions.

Efficiency

A measure of effectiveness given as a ratio, percentage or decimal value (co-efficient) based on actual and possible performance.

Efficiency (energy)

Energy conversion efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The useful output may be electric power, mechanical work, or heat.

Efficient

To produce work without wasting time and energy.

Effort

A force or action that tries to achieve something.

EFI

Electronic fuel injection using sensors, an electronic control unit and fuel injectors to spray fuel into a central throttle body or the inlet ports. Provides very close control of fuel mixture under all operating conditions.

EGO

Exhaust Gas Oxygen Sensor. Also HEGO - Heated Exhaust Gas Oxygen Sensor, EOS Exhaust Oxygen Sensor and Lambda sensor. Provides information to the fuel system ECU on the oxygen content in the exhaust gas.

EGR

Exhaust gas recirculation. An emission control system that uses an exhaust gas feed into the intake air stream to reduce the mass of oxygen in the air charge and limit the formation of harmful oxides.

EGRPS

EGR Valve Position Sensor

EGRT

EGR Temperature

EI

Electronic Ignition

Elastic Limit

Amount of deflection in a spring that can be tolerated before permanent deformation occurs.

Elasticity

The property of materials that can deform and return to their original shape without permanent deformation.

Electric Field

Area round an electric charge in which an electric force is exerted.

Electrical Energy

The potential of electricity to do work.

Electro Motive Force (e.m.f.)

Voltage or pressure in a circuit.

Electro Motive Force (emf.)

Electrical energy available to a circuit at the battery or generator.

Electro Plating

Coating with chromium, silver, etc. by electrolysis.

Electro-coating (Electrophoretic coating)

Electro-coating is an organic coating method that uses electrical current to deposit paint onto vehicle bodies, part, or other assembled products.

Electrode

Usually a metallic conductor which conducts electricity into a liquid, a gas, a vacuum or on to the surface of a solid.

Electrodeposition

A method by which paint is applied electrically by immersing electrodes and the work to be painted in a water-based paint and applying a direct electrical current to them.

Electrohydraulic

A combination of electrical and hydraulic control systems.

Electroluminescence

Electroluminescence (EL) is an optical and electrical phenomenon in which a material emits light in response to an electric current passed through it, or to a strong electric field. It is used on in car entertainment systems and instruments on some vehicles.

Electrolyte

A liquid that conducts electricity. Battery acid is a good example.

Electromagnet

A magnet formed by a soft iron core and an electrical winding about the core. Becomes a magnet when an electrical current flows through the windings.

Electromagnetic

See electromagnet.

Electromagnetic Oscillation

Changes from one value to another in a circuit. Usually produces a sine wave output or similar.

Electromagnetic Solenoid

A solenoid (coil of wire) that is used to operate an actuator such as a fuel injection.

Electromagnetic Valve

A valve that is operated by a coil of wire, which becomes magnetic when switched on.

Electron

Electrons form the outer shell layers of atoms and orbit the protons and neutrons in the nucleus. The electrons have negative polarity and are electrically negative in opposition to the positive charge of the protons.

Electron Shell

Term used to describe the orbit of electrons round a nucleus.

Electronic

Electrical systems operated or controlled by semi-conductor devices.

Electronic Control

System usually based round an electronic control unit where the operation of the system is pre-programmed.

Electronic Ignition

Petrol ignition system in which switching semi-conductors make and break the low tension circuit.

Electrostatic

Describes the electrical state of something as in static (not flowing) electricity.

Element

The basic form of a material.

Email

Electronic Mail. Messages sent from one person to another electronically via a computer.

EMC

Electromagnetic compatibility. EMC requirements stipulate that a device shall not cause interference within itself or in other devices, or be susceptible to interference from other devices.

Emergency Brake

A legal requirement for all vehicles provided by a split hydraulic circuit or a mechanically operated parking brake.

Emery Paper

Carborundum grit on a backing sheet.

EMI

Electromagnetic Interference

Emission Control

Systems on the vehicle to control (limit) toxic emission.

Emission-control

Systems on the vehicle to control (limit) toxic emission.

Emitter

Terminal of a transistor that becomes conductive when the base is energised.

Emoticons

A way of expressing emotions in online communication. E.g., :-)

EMR

Electronic Module Retard

Emulsion

A suspension of fine particles in a liquid. The dispersed particles may be binder, pigments, or other ingredients.

Emulsion Tube

Combined main and compensating jet tubes in a carburettor with provision for drawing air into the fuel flow to create an emulsion at higher engine speeds, thus preventing over-richness and improving fuel distribution.

EN

EN European Standard e.g. BS EN 50342-2:2007 relates to: Lead-acid starter batteries and is a combined British and European standard (Dimensions of batteries and marking of terminals)

Enamel

A paint type which forms a film by absorbing oxygen during curing. Characterised by slow drying and having a highly glossy, finished appearance without polishing.

End Float

Longitudinal play in shaft, intentional or otherwise.

End Play

Alternative term for end float. Longitudinal play in shaft, intentional or otherwise.

Energy

An ability to perform work. SI unit is the 'Joule'.

Engagement

The act of making a connection between two gears of through a clutch.

Engaging Pin

A simple pin used to make a drive connection.

Engaging Plunger

General term to describe a plunger that engages something! Often part of a gearbox.

Engine Analyser

Complex test equipment used to check a variety of engine operating functions and conditions. An oscilloscope is usually included.

Engine Analyzer

Complex test equipment used to check a variety of engine operating functions and conditions. An oscilloscope is usually included.

Engine Block

Main part of the engine that contains the cylinders.

Engine Compartment

The space under the bonnet!

Engine Load

How hard the engine is having to work. For example, accelerating uphill creates a high load.

Engine Management

General term used to describe the control of engine operating functions such as ignition and fuelling. Usually related to electronic control.

Engine Map

A three dimensional map held in a microprocessor that provides an optimum set of values for the control of ignition timing, ignition dwell period and fuel quantities for all engine operating conditions.

Engine Speed Sensor

Provides information on engine speed to engine management systems (transducer).

Engine Support Beams

A bar that is used to support an engine, for example, after the transmission has been removed.

Engine Temp. Sensor

Engine temperature sender unit for temperature gauge and engine management systems (thermistor).

Engine Torque

The amount of turning force produced by an engine. Usually quoted at a set speed.

Enrichment

Process of increasing the mixture strength / reducing the air fuel ratio.

EOBD

European Onboard Diagnostics

EOS

EOS Exhaust Oxygen Sensor. Provides information to the fuel system ECU on the oxygen content in the exhaust gas. Also EGO Exhaust Gas Oxygen Sensor, HEGO Heated Exhaust Gas Oxygen Sensor and Lambda sensor.

EPA

Environmental Protection Agency

Epicyclic Gear

See Epicyclical Gearing.

Epicyclical Gearing

A gear system, consisting in basic form of an internally toothed annulus or ring gear and a central externally toothed sun wheel, with usually three or four planet wheels or gears meshing with the sun wheel and annulus. The planet wheels are often carried as a unit on a planet carrier or spider. Holding the rotation of the planet carrier, annulus or sun wheel will provide a transmission ratio between the two remaining elements. Planetary gear sets can be coupled to increase the available number of ratios.

Epitrochoid

An epitrochoid is a shape traced by a point attached to a circle of radius r rolling around the outside of a fixed circle of radius R, where the point is a distance d from the centre of the exterior circle. It is the shape of the cylinder in a Wankel engine.

EPOS

EGR Valve Position Sensor

Epoxy

A type of paint, adhesive or plastic noted for high mechanical strength, good adhesion and excellent chemical resistance.

EPROM

Erasable Programmable Read Only Memory.

EPT

Exhaust Electronic Pressure Transducer.

ESC

Electronic Spark Control

EST

Electronic Spark Timing

Ester

A type of organic compound used as active solvents.

Estimate

An opinion or judgement.

ET

Emergency Testing – the process by which testing may continue when the computerised system is not available due to a wide scale failure affecting a significant number of VTSs.

Etch Primer

Primer with an acid (usually Phosphoric) content. The purpose of the Etch primer in a coating system is to improve the adhesion and corrosion performance of the undercoat system. Their use is recommended when working with ferrous substrates, and essential on non-ferrous substrates

Etching

The process of a strong chemical cutting into unprotected parts of a metal.

Ethanol

Ethyl-alcohol produced from starches and sugar plants and used as an octane enhancer.

Ethyl Acetate

A fast evaporating ester solvent.

Ethyl Alcohol

An inexpensive, fast evaporating solvent or diluent.

Ethylene Glycol

Anti-freeze. Chemical used to lower freezing point of coolant.

EU

The European Union (EU) is an economic and political union of 27 (as at 2010) member states, located primarily in Europe. Committed to regional integration, the EU was established by the Treaty of Maastricht on 1 November 1993.

Evaluation Circuit

An electronic circuit used to decide a course of action.

EVAP

Emission control system that uses a charcoal canister to prevent fuel tank vapours from venting to the atmosphere. The vapours are drawn into the engine during specific running conditions to purge the canister.

Evaporation

The change from liquid to a gas. When solvents leave a wet paint film, they usually do so by evaporation.

Evaporation Rate

The speed at which any liquid evaporates.

Evaporative Canister

A canister usually containing charcoal that prevents emissions from the fuel tank due to evaporation.

Evaporator

A radiator in the air conditioning system fitted in the heater and A/C housing. The refrigerant passes through the pipes in the evaporator and vaporises to absorb heat and therefore cool the air stream flowing into the vehicle passenger compartment.

Evidence

This is what a candidates needs to produce to prove they have the skills required.

EVP

EGR Valve Position Sensor

EVR

Electronic vacuum regulator solenoid on EGR system.

Excess Pressure Valve

A pressure relief valve that opens if pressure exceeds a set value. Often for safety reasons.

Exhaust Blow-by

Gases from the exhaust bypassing a component, for example, the piston rings or a valve in a turbocharger.

Exhaust Emissions

Substances vented into the atmosphere from an exhaust system.

Exhaust Gas Analyser

An instrument for measuring the constituent gases in the exhaust.

Exhaust Gas Analyzer

See Exhaust Gas Analyser.

Exhaust Gas Recirculation

An emission control system that uses an exhaust gas feed into the intake air stream to reduce the mass of oxygen in the air charge and limit the formation of harmful oxides.

Exhaust Manifold

Heat resisting ducting that connects the exhaust ports of an engine to an exhaust pipe.

Exhaust Ports

Outlets in the cylinder head for the exhaust after the valve opens. In a two-stroke engine the ports are in the side of the cylinder.

Exhaust Stroke

The last stroke of the four stroke cycle when the burnt gases are expelled to the atmosphere.

Expansion

An increase in size. For example, when a metal rod is heated it increases in length and diameter. Opposite of contraction.

Expansion Box

Open muffler in the exhaust system to reduce the noise.

Extender Pigment

An inert, usually colourless and semi-transparent pigment used in paints to fortify and lower the price of pigment systems.

Extension Housing

Usually describes an extra housing on the rear of a transmission gearbox.

External assessment

A test set externally to check portfolio evidence.

External Customer

One outside of an organisation.
F

F

Fahrenheit

F-CAN

Fast CAN

F.W.D.

Front wheel drive."

Face-tone

The colour perceived by the brain when a painted surface is viewed from an angle of 90° - that being the angle at which the greatest amount of light reflection will occur

Factory-applied Paint

Paint applied to a vehicle at the factory of the original equipment manufacturer (OEM). Factory-applied paint is normally cured by baking.

Fading

The gradual loss of colour or gloss of a paint film due to a chemical or physical change, usually due to natural ageing or exposure to harmful environmental conditions

Fail Safe

A device or feature that prevents total failure in the event of a fault occurring.

Fallback

The process by which testing may continue when the computerised system is not available at a VTS, for example, following the breakdown of the VTS device.

Fallback Review

The process by which test data recorded while testing under Fallback is subsequently confirmed on the MOT computer database.

Fan (fan width)

The spray pattern of paint as it is emitted from a spray gun. Most spray guns have adjustments that can alter the fan width from a small round pattern to an elongated elliptical pattern.

Fan Cowl

A protective shield around a fan.

Farad

The unit of capacitance.

Fascia Panel

The panel inside the vehicle below the front windscreen. It carries the instruments, heater ducts and accessories.

Fast Charge

Rapid charge for a battery. 5 times the Ah capacity for about an hour is the recommended maximum.

Fast Idle

The cold engine running speed achieved by a stepped cam on the throttle linkage or by an air bleed valve.

Fatigue

Failure in a material due to excessive and repeated loading usually of an intermittent nature.

Fault

The cause of a problem that results in symptoms

Fault Code

A code generated in and output from an ECU. Used for diagnostics.

Fault-tolerant

In engineering, fault-tolerant design, also known as fail-safe design, is a design that enables a system to continue operation, possibly at a reduced level, rather than failing completely, when some part of the system fails.

FBC

Feedback Carburettor System

FBCA

Feedback Carburettor Actuator

FCS

Fuel Control Solenoid

FDC

Fuel Deceleration Valve

Feather-edge Splitting

Fractures or cracks along the feather-edge which occur during drying or shortly after the topcoat has been applied over primer-surfacer. This problem occurs due to poor preparation, use of excessively fast solvents in primer, improper flash-off time and/or very aggressive solvents in topcoat.

Feather-edging

Tapering a paint edge from substrate to topcoat or between layers of paint material by sanding. If feather-edging has been carried out efficiently, it should not be possible to feel the edges with the finger tips.

Feathering

Term used to describe the way a tyre wears when the tracking is set incorrectly. The tread scuffs up like feathers.

Feed (leather)

The process of treating leather with soaps and creams to improves its lifespan and appearance.

Feed Cable

The main supply wire to a component.

Feedback

A feature used in electronic control systems to monitor performance by the use of a sensor downstream of an actuator. An example is an exhaust oxygen sensor monitoring the fuel injection quantities.

Feedback Resistor

A variable resistor used to indicate position of a moving component.

Feeler Gauge

Set of accurate blades used to set or measure small gaps (valve clearances for example).

Ferrites

These are chemical compounds, ceramic with iron oxide as their main components. Many of them are magnetic materials and they are used to make permanent magnets, ferrite cores for transformers, and in various other high tech applications.

Ferrous

Describes any metal composed of or containing iron, such as low-carbon steel, stainless steel, etc.

FI

Fuel Injection

Fibreglass

Very fine fibres of glass that are supplied as reels of single fibres or spun together as woven matting. It is used in the manufacture of glass-reinforced vehicle bodies, panels, and for component parts and repairs on automobile bodies.

Field (Magnetic)

A magnetic flux about a permanent magnet or live electrical conductor.

Field Circuit

An electrical control circuit for the field coils used to regulate the output from a generator.

Field Coil

An electrical winding round a magnet pole shoe that is used to create a magnetic field when an electrical current flows through the windings. The direction of current flow determines the polarity of the magnetic pole. Used in generators and electrical motors.

Field Coil (Winding)

An electrical winding round a magnet pole shoe that is used to create a magnetic field when an electrical current flows through the windings. The direction of current flow determines the polarity of the magnetic pole. Used in generators and electrical motors.

Filament (Bulb)

The tungsten element in a bulb that glows to produce light.

Filaments

The tungsten elements in a bulb that glow to produce light.

Filiform Corrosion (Spidering)

A paint defect caused by moisture ingress between the substrate and the paint film, e.g. via an untreated stone chip, that continues to travel in 'spidery' threads.

Filler

Commonly, a heavily pigmented sprayed foundation paint used to fill imperfections and pores in a substrate. To avoid confusion with 'Body Filler', should be referred to as 'Primer-Filler' or 'High-Build Filler'

Filler Neck

The connection into the fuel tank for refuelling.

Fillet Radius

A machined curve between two faces of a component. An example is the curve between a crankshaft web and journal.

Film

A very thin continuous sheet of material. Paint forms a film on the surface to which it is applied.

Film Thickness

The thickness or depth of a dry paint film is important. Thin films may appear to be the wrong colour due to their lower opacity, and may also have durability issues. Over-thick films are likely to crack in use. The thickness of paint films on iron or steel surfaces is easily determined with a magnetic gauge.

Film Thickness Gauge

A device used to measure the coating thickness on a substrate. Magnetic devices are used to measure the thickness of ferrous metals; whereas electronic devices are used on non-ferrous substrates.

Filter

A fine mesh or paper screen used to remove dirt and other contaminants from a liquid or gas (air).

Final Drive

The gearing immediately before the driven wheels. It provides a split to each driven wheel with a final gear reduction for the transmission. Can also be used to turn the drive through 90° with the use of bevel gears.

Finesse coat

See 'Drop coat'

Finish

A protective coating of paint; usually referring to the final appearance of the painted surface. Also, to apply a paint or paint system.

Finishing Film

A fine graded abrasive disc for sanding top coat automotive paints before repainting or compounding.

Firewall

Substantial structural panel of vehicle body in front of passenger compartment. Also known as a bulkhead.

Firing Order

The sequence for ignition of individual cylinders in an engine.

Fish Eyes

A surface depression or crater in the wet paint film. Fish Eyes are caused by repulsion of the wet paint by a surface contaminant such as oil or silicone. The depression may or may not reveal the surface under the paint, depending on its depth or severity.

Fish-Eye Eliminator

Additive used in paint to prevent the occurrence of fish eyes (craters/silicones) in a freshly painted surface - usually caused by the presence of contaminants such as wax polish.

Fixed Caliper

A disc brake caliper in which the two halves and pistons are made as a single unit attached to the axle assembly.

Fixed Choke Carburettor

A carburettor with a fixed diameter venturi (choke tube).

Fixed Venturi

A narrowed section in a carburettor - the size of which remains fixed.

Flake

A decorative pigment consisting of flat particles. Usually mica, aluminium or other bright metals, providing special colour effects to the final paint finish.

Flake Orientation

The appearance of the metallic particles in a paint film during and after drying or curing. Selection of the correct flakes in the colour mixing formula and proper application will lead to good flake orientation and thus to good colour match and appearance.

Flaking

A serious paint defect characterised by the paint film lifting and eventually falling off of the substrate.

Flame Plug

Cold start device fitted in the inlet manifold on some direct injection diesel engines.

Flame Trap

Incorporated into the air cleaner unit to prevent the spread of fire caused by fuel igniting in the carburettor if blow back occurs.

Flange

Flat face to flat face butted fitting. Method used to secure exhaust system.

Flange Bolts

Bolts that secure a flat face to flat face butted fitting.

Flange Fitting

Flat face to flat face butted fitting. Method used to secure exhaust system.

Flare Joint

A method of connecting pipes, particularly steel brake pipes, where the end of the pipe is deformed to give a concave or convex flare which is secured with a union nut.

Flash Rusting

A surface rust occurring from improper cleaning or exposing bare metal to the air and moisture for too long of a period.

Flash-off

The first stage of paint drying where some of the solvent content evaporates. This typically dulls the surface from an exceedingly high gloss to a normal gloss or flat appearance.

Flash-off Time

The time between paint application and consecutive coats.

Flashpoint

The temperature at which a liquid will give off a flammable vapour that would ignite when a spark is struck.

Flat (finish)

Lacking in gloss. (See Matting agent)

Flat Seat Valve

A valve that operates by one part operating against a flat component to control flow.

Flat Spot

A temporary drop in power that occurs at the point of initial acceleration when the throttle plate is opened. Occurs as a result of a rise in venturi pressure (drop in vacuum) and a resultant loss of fuel supply into the venturi. Remedied by the addition of an accelerator pump.

Flat-seat Valve

A valve that operates by one part operating against a flat component to control flow.

Flatting

The rubbing down of repaired or pre-painted surfaces with abrasives to achieve the desired shape, prepare the surface for painting or prior to polishing.

Flex Plate

The mounting plate for a torque converter where it is attached to the crankshaft. Fits in place of the flywheel.

Flexible

Being able to accept change.

Flexible Additive

A substance added to paint to improve its performance characteristics, such as impact resistance, flexibility, and elasticity when applied to plastic or flexible substrates.

Flexible Coupling

A rubber or fabric reinforced rubber coupling that is used to join two shafts. Usually incorporates two forks that act as a safety device in the event of failure of the rubber component.

Flexing

Another word for bending.

Flip

The change in value, hue, and chroma of a metallic or pearl car finish when it is viewed from different angles.

Flip-tone

The colour perceived by the brain when a painted surface is viewed from an acute angle (i.e. less than 90°). - the more acute the angle, the less amount of light reflection occurs, giving an impression that the colour is darker

Flitch

A longitudinal cut

Flitch Panel

Structural panel of vehicle body on sides of engine.

Float

A buoyant component used to indicate or control fluid levels. In a carburettor used with a needle valve to control the petrol level in the float chamber.

Float Chamber

Part of carburettor holding petrol at a controlled level.

Floating

The tendency of pigment particles in a wet paint film to separate from one another and concentrate in particular areas, resulting in a 'patchy' finish

Floating Caliper

A disc brake caliper that has a fixed component attached to the axle assembly and a single piston and caliper that is 'floating' by sliding or pivoting on the fixed component.

Flocculation

Clumping together of pigment particles within the wet paint.

Flooding

The tendency of pigment particles to rise to the surface during curing and produce a colour variation at the surface and a lack of uniformity in the colour appearance through the film.

Floppy Disk

A portable disk that stores 1.44Mb of information.

Flow

The levelling characteristics of a wet paint film.

Flow Meter

A sensor that determines flow of a fluid or gas.

FLS

Fluid Level Sensor

Fluid Coupling

A drive coupling that uses a fluid to transmit drive. Also sometimes a viscous coupling.

Fluid Flywheel

A drive coupling that uses a fluid to transmit drive.

Fluid Needle

The part of a spray gun that opens and closes the fluid passage in the fluid tip.

Fluid Pump

A pump for moving or pressurising a fluid.

Fluid Tip

Part of a spray gun that meters and directs the fluid stream.

Flyweights

Weights that act on pivots and move outwards due to centrifugal force.

Flywheel

(1) Component of the clutch. (2) Massive wheel or disc attached, for example, to the crankshaft of an engine, to store energy of rotation and smooth the output from the irregular firing of the cylinders. In many automotive engines, the flywheel incorporates the ring-gear and acts as one friction face of the clutch. (3) Maintains the momentum of the engine.

FO

Fuel Octane Adjustment.

Foaming

A term used to describe the aeration of an oil.

Focal Length

The distance between the focal point and the reflector.

Focal Point

The point within a reflector from where a light source produces parallel beams.

Focussed

To the point.

Follower (Cam)

The component in contact with the cam on a camshaft.

Foot Pound

Old unit of torque. Also pounds/feet. Torque is now given in the SI units of Newton metres (Nm).

Footprint

When applied to tyres describes the area and shape of the part of the tyre in contact with the road.

Force

Exerted to overcome a load.

Force Ratio

The comparison of the force applied to the force produced via some kind of machine or system.

Force-Dry

A method of accelerating the drying of paint with the aid of heat.

Forging

A component forming process applied to hot metal with a hammer or die either by hand or machine. Also hot stamping.

Fork

Part of the door latch mechanism, clutch or gearbox. Fits around another component to hold or move that component.

Fossil fuel

This relates to any fuel made from hydrocarbon deposits such as coal, petroleum, natural gas and, to some extent, peat; these fuels are irreplaceable, and their burning generates the greenhouse gas carbon dioxide.

Four Stroke Cycle

The conventional operating principle for the modern internal combustion engine consisting of the induction, compression, combustion/power and exhaust strokes.

Four Wheel Drive (4WD) (4x4)

Transmission system that uses all four wheels of a vehicle to provide a drive. This term is usually used on vehicles with selectable four wheel drive. The term AWD for all wheel drive is used for vehicles with permanent four wheel drive.

Four Wheel Steering (4WS)

A steering system that applies turning movement to front and rear wheels. The rear wheel steer is initially opposite to the front wheels, neutral and then with the front wheels. This provides steering characteristics that aid manoeuvrability.

Four Wheel Steering 4WS

A steering system that applies turning movement to front and rear wheels. The rear wheel steer is initially opposite to the front wheels, neutral and then with the front wheels. This provides steering characteristics that aid manoeuvrability.

FP

Fuel Pump.

FPR

Fuel Pump Relay.

Fractions

A number of parts out of another number of parts.

Franchise

This is an authorization to sell a company's goods or services in a particular place.

Free Electrons

The electrons in the valency shell of an atom that can link with and move on from other atoms. A material with free electron flow makes a good electrical or heat conductor.

Free Play

The amount of free movement in or between components that is not transmitted to the next component in the sequence. May also be referred to as 'backlash' in some applications such as when applied to gears.

Free Travel

The free play in a clutch linkage before it operates the clutch mechanism.

Freeplay

The amount of free movement in or between components that is not transmitted to the next component in the sequence. May also be referred to as 'backlash' in some applications such as when applied to gears.

Freewheeling

Overrun of a one way clutch. Vehicle movement when the transmission is not engaged to the engine.

Frequency

The number of oscillations per unit of time. Examples are a sound wave or alternating electrical current. The unit for frequency is the Hertz, which equals one oscillation per second.

Friction

Resistance a body encounters in moving over another.

Friction Disc

Term used to refer to a clutch drive plate.

Friction Discs

Component of the clutch. The centre plate that is gripped between the flywheel and pressure plate to transmit a drive to the gearbox input shaft.

Friction Material

A material with consistent performance characteristics used to provide a rubbing surface for brake and clutch components.

Friction Plate

Component of the clutch. The centre plate that is gripped between the flywheel and pressure plate to transmit a drive to the gearbox input shaft.

Front-end Solvent

A fast-evaporating solvent that leaves the paint very soon after application.

FT

Fuel Temperature Sensor.

ft.lb

Foot Pound"

Fuel Distributor

The component in a mechanical injection system that controls and distributes the fuel.

Fuel Efficiency

Performance of engine/vehicle. Rate of fuel usage.

Fuel Filter

A filter to remove contamination from fuel.

Fuel Gauge Sender

Sensor, usually a variable resistor, which supplies information on fuel quantity in the tank.

Fuel Injection

The injection of fuel under pressure into the intake air stream of petrol engines by the use of electrical solenoid valves in place of a carburettor.

Fuel Line

The pipes and hoses that connect the fuel system components.

Fuel Pressure Regulator

In a fuel system the component that keeps the pressure across injectors constant. It consists of a valve, diaphragm and spring.

Fuel Rail

A tube or pipe used to supply fuel to electrical injectors. The quantity of fuel in the rail is relatively large so that the pressure remains constant when the injectors operate.

Fulcrum

A pivot for a lever. Usually a supporting point or shaft.

Fulcrum Ring

A ring on which clutch release fingers pivot.

Full Flow Lubrication

An engine lubrication system where all of the oil flows through the oil filter before entering the engine oil galleries.

Full Load

Describes the engine condition when it is working as hard as it is able - for acceleration for example.

Full Load Enrichment

A device in a carburettor that provides additional fuel during full throttle and heavy load conditions.

Full Wave Rectification

Alternating current converted to direct current by reverse flow of the negative bias so that it is added to the forward bias electrical flow. Modern rectifiers using a diode bridge achieve full wave rectification.

Fully Floating Axle

An axle hub arrangement that carries the load on two bearings and therefore does not apply a shear or bending force on the axle shaft.

Fuse

A safety device in an electrical circuit that will burn and melt to break the circuit when an excess current is applied.

Fuse Box

A central termination block in a vehicle electrical system that carries the fuses.

Fuse Rating

The rated value of a fuse before failure due to an excess current load. The rating can be either a constant or a surge value and is given in amps. Fuses are usually colour coded and marked for the fuse rating.

Fuzzy Logic

A digital control system that makes 'educated' guesses.

FWD

Front-Wheel Drive
G

G or g

Unit of force equivalent to the force of the Earth's gravity.

G-force

A force on an object equivalent to the force applied by the Earth's gravity.

G/C Clamp

A clamp (hand tool) shaped like a G/C.

Gaiter

A rubber (or similar) boot used to cover working components. It is used to keep dirt out and in some cases lubrication in place. Also slang for alligator...

gal

Gallon

Galleries

See Main Gallery.

Galvanize

A protective process for steel sheet where a thin surface layer of zinc is applied by hot dipping the steel into a bath of molten zinc.

Ganged Switch

An electrical switch that operates two or more circuits from one switching point.

Gas

A fluid state of matter when the atoms are free. The least dense state of matter which can have three states, solid, liquid and gas.

Gas Analyser

Electronic equipment that measures exhaust gas constituents.

Gas Analyzer

See Gas Analyser.

Gas Turbine

A type of internal combustion that uses rotating blades in a compressor to provide charging of the combustion chamber. The output gas pressure is used to drive turbine blades which are connected by a shaft to drive the compressor and a transmission gearbox or in the case of aircraft jet engines to provide air propulsion.

Gasket

A material that is fitted between faces to take up the irregularity of the surface finishes and provide a gas or liquid seal.

Gasoline

A hydrocarbon fuel made up from carbon and hydrogen elements. Used as a fuel for internal combustion engines. Also petrol.

Gassing

The formation, in the can, of gaseous products in a coating material, due to the reaction between two or more constituents of the coating material or between the latter and the metal of the container. Characterised by a 'Pop' sound when opening paint containers

Gate

In transmission systems a device to guide a gear into any one position at any one time. In electronics a logic device for regulating electrical current flow according to input voltage levels.

GCM

Governor Control Module.

GDi

Gasoline direct injection. Petrol/Gasoline is injected directly into the combustion chamber under high pressure.

Gear

A method of providing leverage. Toothed wheel that meshes with another toothed wheel.

Gear Brake

Part of an automatic gearbox, the brake is often a band of friction material.

Gear Cluster

A series of fixed gears on one shaft. Used to provide gear selection by engagement with freely rotating gears on another shaft. The selection is made by locking the freely rotating gear to the shaft. This can be by the use of a sliding hub or a sliding gear splined to the output shaft.

Gear Clutch

A clutch that connects or disconnects drive to a gear.

Gear Cogs

Toothed wheels that mesh with other toothed wheels.

Gear Lash

The clearance between the teeth of two meshing gears. Also known as backlash when applied to gears.

Gear Pump

An oil pump using two meshed gears to provide a positive pumping action. The teeth are of the two gears run in mesh. Where they come out of mesh a small chamber forms to allow oil to flow in, the oil is carried round the periphery of pump in the gear teeth and when the teeth come into mesh the chamber is reduced in size and the oil forced from the pump.

Gear Ratio

Ratio of angular velocities of pairs of meshing gears. Number of teeth on driven gear divided by number of teeth on driver gear.

Gear Reduction

A gear drive that reduces the rotational speed of the output shaft below that of the input shaft.

Gear Train

Two or more gears in mesh that transmit a drive through them.

Gearbox

A housing containing gears to allow different ratios to be selected.

Geared Distributor

A distributor driven by a gear from the engine.

Gearshift

The mechanism for selecting gears in the transmission. Consists of the driver's gear lever, the linkage to the transmission gearbox, and the selectors in the gearbox.

GEM

Governor Electronic Module.

GEN

Generator.

Generator

Machine for converting mechanical energy into electrical energy.

Generic

A common type or something that is used for a variety of tasks.

Gerotor Pump

A type of positive displacement oil pump that uses two gears on eccentric axes. One gear is on a shaft inside another rotating in the housing. The pumping and carrying chambers are formed between the gear teeth.

Glare

Reflection from the sun or a light onto the computer screen making it difficult to see properly.

Glaze

A polish that is safe for use on fresh paints. Some glazes contain a mild abrasive that will remove minor surface imperfections. When a glaze with an abrasive is used, it should be followed by application of wax on cured paint or a hand glaze on fresh paint. A glaze also does not contain silicone.

Glazier

Person who works with glass.

Gloss

The ability of a surface to reflect light. Measured by determining the percentage of light reflected from a surface at certain angles.

Gloss Meter

An apparatus for measuring the gloss of paint film.

Glow Plug

Cold start device for diesel engine. Fitted into the combustion chamber and heated by an electrical current so that the injected air and fuel is heated as an aid to ignition when the engine is cold.

GND

Ground.

Google

Popular Search Engine.

Governor

A control device that limits the speed of a unit or controls or senses the operation of a unit. An example is the governor in a diesel injection pump which controls the engine speed.

Governor Pressure

The control pressure in an automatic transmission that senses vehicle speed. It is applied to the hydraulic control unit or valve body to effect gear shifts in relation to vehicle speed.

Governor Valve

The valve in an automatic transmission, which is fitted on the output shaft. The rotational speed acts on a spring-loaded valve to regulate pump pressure. The governor pressure acts on the gear shift control plunger in the valve body.

GPM

Grams Per Mile

GPS

Global Positioning System: This is a navigational system involving satellites and computers that can determine the latitude and longitude of a receiver on Earth by computing the time difference for signals from different satellites to reach the receiver.

Grab (Brake)

A braking condition where the brakes lock up when light pedal effort is applied. Caused by brake linings digging into the drum or disc on application. Usually cured by forming a chamfer on the leading edge of the lining.

Grammar

Forming well written, easy to read sentences, paragraphs and documents with the use of punctuation (i.e., full stops, commas etc.).

Gravelometer

A device that propels rocks at a painted substrate to measure the resistance the finish has to rock chips.

Gravity

The attraction that all masses experience as a force towards the earth - or any other planet for that matter!

Gravity-feed Gun

A spray gun which has the paint container on the top of the gun, allowing the paint to flow into the fluid passage by gravity.

Grease

A thick sticky lubricant made from a variety of bases, usually derived from crude oils, and used for bearing and chassis lubrication.

Greenhouse gases

Gases that are a natural part of the atmosphere. They absorb and re-radiate the sun's warmth, and maintain the Earth's surface temperature at a level necessary to support life.

Grinding

Abrading painted or unpainted metal surfaces to remove paint/corrosion or prepare the area for filling.

Grit

Refers to the abrasive size used in flatting papers, discs, etc. and is classified using 'P' grades, e.g. P40, P120, P600 and so on. The larger the number, the finer the abrasive

Gritty

A paint product is said to be gritty when it contains large particles, from insufficient dispersion during mixing or when it contains large hard particles of foreign materials.

Grommet

A blind grommet is a rubber insert fitted into a hole in a plate to blank off the plate. Other types are used to provide protection for cables or pipes that pass through a hole.

Groove (Tire)

A channel cut in the tread of a tire to facilitate the dispersal of road surface water.

Groove (Tyre)

(1) A channel cut in the tread of a tyre to facilitate the dispersal of road surface water. (2) The machined slot around the piston into which the rings are fitted.

Ground (Earth)

The electrical termination for components connected into a vehicle direct current ground return circuit. On mains electricity a safety route for an electrical short circuit used as a means of protecting people or electrical components from electrical overload.

Ground (Earth) Cable

The battery cable connecting the return side of a vehicle circuit to a terminal on the battery where a ground return circuit is used.

Ground Clearance

The dimension under a vehicle which clears any obstacles in the roadway.

Ground Test

A test to make sure the earth or ground or chassis electrical connection is in good working order.

Grounding

A safety practice where two objects are interconnected with clamps and bare wire. This equalizes the electrical potential between the objects and helps prevent static sparks that could ignite flammable materials.

Gudgeon Pin

The piston pin that connects a piston to a connecting rod. Fitted at the little end of the connecting rod. Also wrist pin.

Gum

Petroleum distillate formed during combustion particularly with poor fuel quality. The gum is deposited on cylinder walls and increases the tendency for glazing.

Gun Body

The main part of the spray gun to which all other component parts are attached.

GVW

Gross Vehicle Weight
H

H.A.S.W.A

Health And Safety at Work Act 1974.(UK)"

H20

Water

Half Shafts

Shafts by which power is transmitted from final drive to driven wheels in an enclosed axle.

Hall Generator

An electronic pulse generator using the Hall effect of a semiconductor to provide information to the ignition amplifier or ECU on engine position and speed.

Hall IC

Integrated circuit as part of a Hall sensor.

Hall Sensor

An electronic pulse generator using the Hall effect of a semiconductor to provide information to the ignition amplifier or ECU on engine position and speed. Also used for sensing road speed etc.

Halogen

A description of a series of gases such as argon.

Handbrake

Hand operated parking brake usually with a mechanical linkage. Also forms the reserve or emergency brake on many vehicles.

Handbrake Cable

A cable that operates the brakes when a lever is pulled.

Handbrake Linkage

Cables or rods used to operate the parking/handbrake.

Hard Disk

A storage device that holds large amounts of data.

Hardener

A chemical specifically designed to ensure cure of a paint finish, filler, stopper, resin or adhesive. Also, another name for an activator.

Hardware

The physical components of a computer system.

Hardwired

A physical connection between two or more electrical devices.

Harmonic Balancer

Rotating or oscillating engine balance shaft.

Harness

The collection of vehicle cables wound together with an insulation tape. Also known as a 'wiring loom'.

Hazardous

Risky. Potential to harm people or property.

Haze

The development of a cloudy area in the paint film or in a clear liquid.

HC

(1) Hydrocarbon. (2) High compression.

Head Gasket

Seal between cylinder block and cylinder head.

Head-on

Viewing a repaired/re-painted area from an angle that is perpendicular (at 90°) to the car.

Head-up Display

Projection of instruments onto the windscreen so that the road and the instruments can be seen at the same time by the driver.

Header Tank

The expansion tank at the top of a coolant radiator, which can be part of the radiator or a separate tank.

Headlamp

Vehicle lighting that provides illumination of the road for the driver. Usually consists of switched main and dipped beams.

Headway Sensor

A device usually fitted in the front grill of a vehicle that in conjunction with a transmitter senses distance in front of the vehicle. Often part of an active cruise control system.

Heat

A form of energy in all materials that can be used to do work.

Heat Exchanger

A device for transferring heat from one system or place to another.

Heat Range

Applies to spark plug construction where the rate of heat loss from the plug nose is controlled by the length of the insulation. Spark plugs are given a rating from hot to cold to classify the heat range and application. The plug tip temperature is controlled to keep the tip and electrodes clean.

Heat Sink

A plate to which electronic components are attached to dissipate heat.

Heater Matrix

Small radiator used to exchange heat from the coolant to the vehicle cabin.

HEGO

Heated Exhaust Gas Oxygen Sensor. Also EGO Exhaust Gas Oxygen Sensor, EOS Exhaust Oxygen Sensor and Lambda sensor. Provides information to the fuel system ECU on the oxygen content in the exhaust gas.

HEI

High Energy Ignition. A distributor ignition system using electronic control of the coil secondary output.

Helical Gear

A gear with teeth cut at an angle.

Helical Rotor

A turbine or compressor in a turbocharger often has vanes that are helically shaped.

Helical Spring

Metal spring used in vehicle suspension. Also known as a coil spring.

Hemisphere

A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball - a hemisphere is half a sphere

Heptane

A fuel used in research tests as a comparison when determining the octane rating of fuels. Octane value of zero.

Hertz

The number of oscillations per unit of time. The SI unit for frequency is the Hertz which equals one oscillation per second.

Hex

Short for hexagonal.

Hg

Mercury

Hide Mallet

Soft hammer made of hide (leather). Plastic types are also used.

Hiding or Hiding Power

(See 'Opacity')

High Boilers

Solvents with boiling points above 100 degrees Celsius.

High Lift Cam

A special cam profile used on performance engines to increase the opening size of a valve.

High resistance

An unwanted resistance in a circuit that causes it to operate incorrectly.

High Solids

Paints are described as having high solids when they contain more than 50-60% solids. High solids paints have lower VOC's.

High Tension

The term used for the high voltage in the secondary circuit of the ignition system.

HLG

Hall generator. A sensor using a Hall effect to provide signals to an ECU.

HO2S

Heated Oxygen Sensor

Hoist

To lift something or a term used to describe a vehicle lift or ramp.

Hold-in Winding

A winding in a starter motor solenoid that holds the switch contacts together and the drive pinion in mesh during engine starting.

Holdout

The ability of a surface to keep the topcoat from sinking in and causing a decrease in appearance or gloss.

Homogenous

Uniform in structure or composition throughout. This is usually used to refer to a fuel air mixture in a cylinder that is a 'perfect' mixture of fuel and air.

Hone

A light grinding process applied to cylinder bores in preparation for the fitting of new pistons.

Hooke's Joint

A drive shaft universal joint consisting of two yokes and a cross bearing. Also Cardan joint.

Horizontally Opposed

An engine configuration where cylinder pairs are fitted on opposite sides of the crankshaft. Sometimes referred to as 'Boxer' engines.

Horsepower

A measure of power equivalent to 0.746 Kilowatts. Defined by a rate of doing work of 33,000 foot pounds per minute (550 foot pounds per second).

HOS HO2S

Heated Oxygen Sensor.

Hose Clamp

Simple ring type clamp to seal a hose onto a pipe.

Hot Idle Compensator

A device to change idle or mixture settings when an engine is hot.

Hot Spray

The technique of applying paint at elevated temperatures. The elevated temperature reduces the viscosity so that higher solids materials can be sprayed, and allows application with less solvent.

Hot Stamping

A machine forging process using a series of dies to create the completed shape.

Hot Wire

A small thin wire that is heated an placed in an air flow. The change in temperature is used to determine the rate of air flow.

hp

Horsepower

HT

High Tension

HT Cables

High tension leads (high voltage) used to supply the spark.

HT Leads

High tension leads (high voltage) used to supply the spark.

Hub

Centre of a wheel or gear or similar.

Hub Nut

Main nut that secures a wheel hub.

Hue

The quality by which colours are distinguished from one another, such as">a red from yellow, blue, green, or purple, and all shades in between.

Hunting

Uneven running of an engine, usually when the mixture is over rich.

HVAC

Heating, ventilation and air conditioning.

HVLP (High Volume, Low Pressure)

Describes a paint gun that uses a high volume and low pressure of atomising air to apply material to a surface. This provides high transfer efficiency and lower overspray.

Hybrid

A hybrid vehicle is a vehicle that uses two or more power sources to move the vehicle. The term most commonly refers to hybrid electric vehicles (HEVs), which combine an internal combustion engine and one or more electric motors.

Hybrid vehicle

Vehicles that use both a traditional engine (combustion) and a rechargeable system (typically operated by a battery) to improve mileage, cause less pollution, and decrease need for fossil fuel.

Hydraulic

A system for transmitting and modifying force by the use of a liquid. Consists of a pump, control devices, hydraulic lines and slave cylinders.

Hydraulic Brake

Brake actuated only by hydraulic pressure.

Hydraulic Clutch

A clutch, operated by fluid pressure.

Hydraulic Hoses

Hoses that carry fluid under high pressure.

Hydraulic Lifters

Hydraulic cam followers in the valve opening mechanism.

Hydraulic Pedestal

Self-adjusting support for a finger tappet in the valve opening mechanism.

Hydraulic Pressure

Pressure applied by a fluid.

Hydraulic Tappets

Self-adjusting cam followers in valve opening mechanism.

Hydraulic Valves

Valves used to control pressure or flow of a hydraulic fluid.

Hydrocarbon

A compound which contains only carbon and hydrogen, which are distillate by-products of petroleum, natural gas and coal.

Hydrocarbon (HC)

Chemical compound which contains only, or principally, Carbon and Hydrogen. The principal constituent of liquid fossil fuels.

Hydrocarbon Emissions

Fuel vapours released into the atmosphere from a vehicle exhaust or fuel tank.

Hydrocrack

To break down (a hydrocarbon) by the process of hydrocracking. This is a catalytic cracking process of breaking down large hydrocarbon molecules into smaller ones

Hydrolysis

Reaction with water. Usually refers to a decomposition process leading to paint failure.

Hydrometer

Instrument used for measuring specific gravity/relative density of a liquid (coolant, battery electrolyte).

Hydropneumatic Suspension

A suspension system using a liquid to transfer suspension movements to pneumatic (gas) springs.

Hygrometer

Instrument used for measuring relative humidity - in an automotive context it is used to check moisture content of brake fluid.

Hygroscopic

A paint film or other solid that readily absorbs water.

Hypoid Gearing

Bevel gear with the axes of the driving and driven shafts at right angles, but not in the same plane, giving some sliding action between teeth. Widely used in rear axle final drives.

Hysteresis

A characteristic of materials, sensors and sometimes instruments to make their behaviour dependent on the immediate history to which they have been subjected. Typically the final settling point is different when approached from above to when it is approached from below
I

I.F.S

Independent Front Suspension. Also inertia fuel shut off switch used to switch off an electrical fuel pump or diesel fuel pump solenoid when the vehicle is involved in an accident."

I.R.S

Independent Rear Suspension."

IA ISA

Idle adjust. Idle speed adjust.

IAC

Idle Air Control

IAT

Intake air temperature sensor used in electronic fuel injection as a correction factor for the quantity of fuel to be delivered.

IATS

Intake Air Temperature Sensor

IC

Integrated Circuit

ICE

In Car Entertainment system.

ICM

Ignition Control Module.

ICS

Idle Control Solenoid

ICT

Information and Communication Technology.

ID

Inside Diameter

IDI

Indirect injection of diesel fuel into a pre-combustion or swirl chamber in the cylinder head.

Idle

Term used to describe an engine running at a speed when the throttle has not been depressed. Also used to describe a lazy technician...

Idle Air Control (IAC)

Idle air control. An air valve on fuel injection systems to increase the air flow and idle speed of a cold engine and during warm up.

Idle Control Components

Parts that are designed to keep the engine idle speed at a set level.

Idle Mixture

The fuel strength or air/fuel ratio.

Idle Speed

Rotational speed of an engine on no-load and minimum throttle setting. Also tick over and curb idle.

Idler Arm

A steering arm parallel to the Pitman arm (drop arm) and connected to it by a centre track rod.

Idler Gear

(1) A gear between two others that does not affect the gear ratio. Any gearwheel between the driving and driven gears in a gear train, the shaft of which serves only to bear and locate the gear, and is therefore 'idle'. The idler gear may serve to reverse the rotation of the driven wheel, so that it rotates in the same direction as the driving wheel. (2) An intermediate or tensioning pulley for a belt drive.

Idling

Describes an engine running at idle speed (usually 700 to 800 rev/min).

IEC

International electrotechnical commission

IFI

Indirect Fuel Injection

IGBT

The insulated gate bipolar transistor or IGBT is a three-terminal power semiconductor device, noted for high efficiency and fast switching.

IGN

Ignition

Igniter

The part of an air bag unit that sets the inflation process in to action.

Ignition - IGN

Starting of combustion. Setting fire to a flammable substance. In a petrol engine the spark jumping the spark plug electrodes that starts the combustion process.

Ignition Advance

The automatic bringing forward of the ignition spark in relation to the engine speed.

Ignition circuit

The system used to connect components involved in producing a high voltage at the spark plugs.

Ignition Coil

An electrical transformer that increases the battery voltage to a high tension capable of arcing across the gap of spark plug electrodes.

Ignition Coil - IGC

An electrical transformer that increases the battery voltage to a high tension capable of arcing across the gap of spark plug electrodes.

Ignition Distributor

A component in the ignition system that houses the primary circuit switching device and the secondary circuit distribution components.

Ignition Lag

A short delay after injection before the fuel ignites.

Ignition Module

The electronic unit that switches the ignition coil on and off in response to a signal from a pulse generator.

Ignition Switch

The engine ignition and vehicle electrical circuits control switch used by the driver to start and stop the engine.

Ignition Timing

The static and dynamic settings of the ignition distributor or in the engine control module (ECM) that control the ignition coil secondary circuit output and spark for starting the combustion process in the engine.

Illumination

Lighting up, making bright.

IMA

Integrated Motor Assist is Honda's term for their hybrid propulsion system. This includes the electric motor/generator, 144v battery pack, controlling electronics and the wiring that connects them all together. ISG or ISA is used by some manufacturers, Integrated Starter Generator or Alternator.

Immediately

Taking place without delay.

Immiscible (non-miscible)

Incapable of mixing in or blending with other components.

Immobiliser

Usually part of an alarm system. It cuts off the ignition or fuel to prevent a vehicle from being started and stolen.

Impact Switch

A switch that operates when the car impacts something. Used as a safety device to cut off a fuel pump.

Impact Tools

Power tools that use a high frequency hammering action for the removal and installation of nuts and bolts, for drilling and chiselling. Impact tools should only be used with sockets, drills and chisels made for that purpose. The use of normal hand tools form impact is hazardous as these may shatter in use.

Impeller

Vaned disc that creates flow by centrifugal force (water pump). In a torque converter it is driven from the engine to force liquid onto the turbine.

Imperial

Old British standard of measurement using yards, feet and inches.

Imperial Measurement

Defined by three measures - the gallon, the yard and the pound.

In-line Engine

A engine fitted along the axis of a motor vehicle.

Inboard Brakes

Brake units fitted on the final drive casing and output shafts rather than on the wheel hub and carrier.

Incandescence

Light given off by a high temperature object. Usually describes a bulb filament.

Included Angle

Camber and steering swivel (king pin) inclinations (angles) added together.

Incoming Telephone Call

To receive a telephone call.

Independent Suspension

Suspension fitted to each wheel."

Indirect Injection

Diesel engine design where fuel is injected into a pre-combustion chamber fitted inside the cylinder head.

Induced Voltage

Naturally occurring voltage in a conductor when subjected a magnetic flux.

Inductance

Property of a coil such that an increase in current causes an increase in magnetism, which in turn tends to prevent the original increase in current. See also Lens's law.

Induction

1. The drawing in of a gas or fluid. 2. Process of causing an electrical potential in a conductor due to relative movement of a magnetic field.

Induction Period

An allotted amount of time upon mixing of components for compatibilization. The process is common among the use of epoxy/polyamide coatings.

Induction Stroke

First stroke of four stroke cycle when air and fuel enter the engine as the piston moves down the cylinder. Also known as the intake stroke.

Inductive Coil

All coils possess inductance. This is the property that resists changes in current flow.

Inductive Generator

A magnetic/electrical pulse generator used as a sensor in electronic control systems. It uses an iron core and electrical winding to induce an electrical current when passed by a toothed wheel or rotor. Also known as a magnetic pulse generator.

Inductive Sensor

A coil and magnet used in conjunction with a trigger wheel. It produces a sine wave output with a frequency proportional to speed.

Industrial Fallout

Chemical compounds present in the air which are deposited on the horizontal surfaces of vehicles and which may damage the finish.

Inert Gas

A non-reactive gas element.

Inertia

The force that holds a body stationary or in uniform motion.

Inertia Reel

Type of seat belt that holds spare webbing on a reel and locks the reel on impact. This is performed by a swinging weighted ball and lever that locks the belt reel ratchet wheel with a pawl.

Inertia Switch

A switch that operates by the inertia (need to stay at a constant speed or state of rest) of a mass. Usually used to cut off supply to a fuel pump in case of a crash.

Inflation

The general increase in the price of goods and services.

Infrared

Light energy that produces radiated heat, used for speeding up the curing of paint, filler, etc.

Infrared Light

That portion of the spectrum responsible for most of the heating effects of the sun's light. Not visible to the human eye.

Infrared Lighting

Infrared light is outside the visible spectrum. When used for lighting, a special detector is also needed.

Infrared Sensor

A sensor that is sensitive and produces a signal in response to infrared light.

Ingestion

Take in by swallowing or absorbing.

Inhalation

Breathing in.

Inhibit

To hinder or to restrain progress.

Inhibitor

A chemical added to retard or prevent a particular reaction.

Inhibitor Switch

A simple switch that prevents the operation of a circuit. A good example is the switch in an automatic transmission gearbox that prevents operation of the starter motor when drive or reverse is engaged.

Inhibitors

A chemical that restricts or reduces the chemical reactions. In a cooling system an inhibitor is added to prevent corrosion of the engine from the ethylene glycol content of the antifreeze.

Initial diagnostic assessment

This is carried out to find a candidates strengths and weaknesses, current levels of attainment and potential.

Initiator

A chemical added to help start a chemical reaction such as polymerization or curing.

INJ

Injector valve.

Injection

Of fuel by pressure into inlet manifolds (petrol) or combustion chamber (diesel).

Injection Lag

A short time delay between actuation and actual operation of an injector.

Injection Timing

Point within the four-stroke cycle when injection occurs. Similar to ignition timing on petrol engines.

Injector

Control valve and nozzle used to inject and atomise fuel.

Injector lag

A short time delay between actuation and actual operation of an injector.

Injector Nozzle

The tip of a fuel injector, which is drilled to produce a particular spray pattern.

Injector Pulse Width

When viewed on an oscilloscope, the horizontal width of the trace. This represents the open time of the injector.

Injector Pump

Fuel pump that produces the timed high pressure pulses for the injection and timing of fuel delivery on a diesel engine.

Inlet Manifold

Ducting that connects the carburettor/fuel injection components to the inlet ports in the cylinder head.

Inlet Ports

The way in to the engine for fuel/air mixture.

Inlet Valve

Valve in the inlet port that allows air or air/fuel mixture into an engine.

Inline Pump

Type of diesel fuel injection pump with the pump elements in line.

Inner Races

The inside rings of ball or roller bearings.

Inner Tube

The separate sealed air tube on a tyre that is required with certain types of tyre and wheel rim.

Inner Wing

Metal panel structure under the bonnet forming part of the wing.

Input

Power or data that goes into a mechanical unit or electronic control module.

Input Device

A device that allows you to put information into the computer. Egg, keyboard, mouse.

Input Shaft

Shaft that takes drive from the engine into the gearbox.

Insert (Valve Seat)

A steel insert fitted in aluminium and some iron cylinder heads to form a durable seating for the inlet and exhaust valves.

Inshot

A feature of air brakes designed to give an initial quick application to make up for the time it takes for air pressure change.

Instrument Lights

Illumination for instruments such as the speedometer.

Instrument Panel

The panel in a vehicle fascia that holds the instruments and warning lights. Also dash panel and dashboard.

Insulated Circuit

A vehicle wiring system that does not use the body and chassis as a ground to form a return electrical circuit to the battery and alternator. A separate insulated set of cables connects all components to complete the circuits. Used in vehicles where there is a high fire risk. (Fuel tankers).

Insulation resistance

The resistance to current flow of the insulating materials between circuits and contacts.

Insulator

Restricts the flow of electricity or heat through the material.

Intake Manifold

See inlet manifold.

Intake Stroke

Alternative term for the induction stroke. First stroke of four stroke cycle when air and fuel enter the engine as the piston moves down the cylinder.

Integral Body Construction

Modern light vehicle body and chassis construction method which has no separate chassis. The strength is built in by the use of stressed and reinforced panels.

Integrate

To incorporate something into something else or to unite into a whole.

Integrated Circuit (IC)

An electronic device consisting of transistors, diodes and other components in a single unit and usually having a specific function.

Integrity

Data corruption refers to errors in computer data that occur during transmission, retrieval, or processing, introducing unintended changes to the original data. Computer storage and transmission systems use a number of measures to provide data integrity, or in other words the lack of errors.

Intelligent device

A component that has some ability to monitor itself and react to changes.

Intensifier

A device which converts low pressure fluid power into higher pressure fluid power (used by some injection systems)

Inter-Quartile Mean

The average of the values in the inter-quartile range.

Inter-Quartile Range

The range of numbers with the upper and lower quartiles removed.

Interactive

Two-way communication.

Intercooler

An air to air radiator type heat exchanger fitted after a turbocharger in the air intake ducting to cool the intake air before it enters the engine.

Interference Fit

The relationship between the dimensions of two components where one fits inside the other. In this instance the fit is one where the inner dimension of the outer component is less than the outer dimension of the inner component.

Interior Lights

Lights inside a vehicle for illumination purposes.

Interleaf Friction

Friction between spring leaves that produces a damping effect.

Interlock

Part of a manual gearbox selector mechanism that prevents the engagement of two gears at the same time.

Intermediate Gear

Any gear in a transmission gearbox other than top and bottom or reverse.

Intermediate Shaft

A shaft between the input and output shafts, usually as part of a gearbox.

Internal Combustion

Engine where fuel is burnt inside cylinders.

Internal Customer

One inside of an organisation.

Internal Damping

A feature of some suspension components where friction tends to reduce oscillations.

Internal Resistance

Describes the resistance of a component that is the combination of all its internal parts. Even a battery has some resistance inside it.

Internal Splines

Splines (teeth) inside a shaft or tube.

Internal Taper

A hole that narrows.

Internal verification

The process whereby a centre ensures it operates consistently and to national standards in interpreting and assessing the key skills.

Internal Windings

Windings inside a component.

Internet

A worldwide network of computers that allows us to view the World Wide Web.

Interpret

To understand and be able to explain something.

Intimidating

To make somebody feel uncomfortable, timid or even fearful.

Ion

An atom with positive or negative charge due to gain or loss of an electron.

IPU

Integrated Power Unit.

Iridescents

All colours that contain aluminium, mica, or other particles that impart a metallic appearance to the colour.

Irradiation Treatment

A process where something is acted upon by radiation from a radioactive substance - it is used to make some foodstuffs last longer - but is a contentious issue!

IS

Inertia Switch.

ISC

Idle Speed Control. This term is usually used when a stepper motor or solenoid is used for idle speed increases during engine warm-up and when ancillary systems are in use.

ISO

International Standards Organization

Iso-octane

A fuel used in research tests as a comparison when determining the octane rating of fuels. Octane value of 100.

Isocyanate

A chemical found in the hardening agent used with acrylic urethane and other two component reaction type paints. The introduction of Isocyanates in hardeners led to the requirement for air-fed respirators in the vehicle painting industry

IT

Information Technology

ITCS

Ignition Timing Control System

ITS

Idle Tracking Switch
J

Jack

A mechanical or hydraulic tool for lifting a vehicle. Should always be used with axle stands if under vehicle access is needed.

Jack Stands

Vehicle support equipment manufactured with a rated weight capacity. Used to support a vehicle when wheels are removed or when access to the underside is needed. Also known as axle stands.

Jam (Lock) Nut

A nut that is used to lock another nut or threaded component in position on a threaded rod or stud. Also lock nut - US term.

Jamb Switch

Switch fitted on a door jamb or pillar for operating the courtesy light or vehicle alarm system.

Jamming

The deliberate radiation or reflection of electromagnetic energy for the purpose of disrupting enemy use of electronic devices or systems. Or informal music creation in a group!

JAS

Jet Air System

Jet

A calibrated nozzle in a gas or liquid injection system. In a carburettor used to regulate fuel and air flows.

Jet Needle

A small needle that works inside a jet (small hole) to control fuel flow in a carburettor.

Jig

A device for locating and holding a piece of work during machining operations.

Jiggle pin

Most thermostats have a Jiggle pin. Its function is to allow trapped air past a closed thermostat as a build-up of air in front of the wax capsule could cause engine damage.

Jounce

Suspension bump travel due to the wheel hitting an irregularity in the road surface. Also applies when the suspension is pushed down. Also known as bounce.

Journal

The surface hardened cylindrical part of a shaft that forms part of a bearing. The journal rotates in round sleeve or split shell bearings.

Joystick

A control stick that operates a system.

Judder

Irregular braking or clutch operation with intermittent snatching.

Jump Leads

Heavy duty electrical cables used to connect a slave battery to a vehicle with a discharged battery for starting. Also jumper cables.

Jump Start

Starting a vehicle engine with the aid of a slave battery and jump leads.

Jumper Cables

Heavy duty electrical cables used to connect a slave battery to a vehicle with a discharged battery for starting. Also jump leads.
K

KAM

See Keep Alive Memory.

KDS

Kick Down Switch.

KE-Jetronic

A mechanical injection system from Bosch, but with some electronic control.

Keep Alive Memory (KAM)

Part of a microprocessor RAM that holds temporary data for a specified duration. The KAM requires a constant voltage to retain data. It is cleared when the power is turned off.

KERS

A kinetic energy recovery system is an electric generation, storage, and propulsion system used in Formula One (up to 2010 anyway), which generates electricity during slow down, stores energy in batteries or a flywheel, and boosts acceleration with electric drive motors assisting the engine. Many hybrid cars are similar.

Key

A locating device that sits in slots on a shaft and pulley or gear wheel. Also known as Woodruff key.

Key Data

Important, relevant information.

Keyboard

The typewriter-like keys used to input data into a computer. An input device.

kHz

Kilohertz

Kick Down

A switch of a cable on an automatic transmission signals that the throttle is at least 90% open. Under certain conditions this causes a downshift for improved acceleration.

Kick Down Switch

Switch on an automatic transmission that signals that the throttle is at least 90% open. Under certain conditions causes a downshift for improved acceleration.

Kick-out

The precipitation of dissolved binder or additive from solution as a result of solvent incompatibility.

Kickback

Road shocks transmitted to the driver through the steering system.

Kilowatt

1000 watts

Kinetic

Movement energy.

Kinetic Balance

The balance of a rotating component about the perpendicular to the axis. Wheel balance has both static and dynamic quantities.

Kinetic Energy

Energy in the form of a mass moving.

King Pin Angle

Alternative term for KPI (King Pin Inclination).

King Pin Inclination

The angle that the king pin axis tilts from the vertical. Used to provide centre point steering where the centre of the tyre tread is on the steering pin axis.

King Pins

A type of steering swivel fitted to beam axles.

Km

Kilometres

KNK

Knock signal from an engine knock sensor to the ECM.

Knock

Advanced or quick detonation of fuel in a cylinder where the resultant pressure rise causes a shock wave through the piston, crankshaft and engine block.

Knock Sensor

A piezoelectric sensor used to provide sensor signals to an ECM when an engine is knocking. A closed loop control retards the ignition to prevent knock.

Knocking

Used to describe engine knock or a noise produced that sounds like one object hitting another.

Knowledge

Knowledge is defined by the Oxford English Dictionary as (i) expertise, and skills acquired by a person through experience or education; the theoretical or practical understanding of a subject; (ii) what is known in a particular field or in total; facts and information; or (iii) awareness or familiarity gained by experience of a fact or situation.

Knuckle (Steering)

Steering stub axle assembly. Also known as a steering swivel.

KOEC

''Key On, Engine Cranking''

KOEO

''Key On, Engine Off''

KOER

''Key On, Engine Running''

kPa

Kilopascals - unit of pressure.

KPI

King Pin Inclination or the angle that the king pin axis tilts from the vertical.

KS

Knock Sensor.

KV

Kilovolts
L

L

Litres

Lacquer

A deposit that builds up in fuel components. It is similar to varnish.

Lacquers

Paints that dry by evaporative loss of solvent, e.g. Cellulose and 1K Acrylics. The film remains soluble in and susceptible to attack by the same or similar solvents.

Ladder Chassis

A chassis construction consisting of two longitudinal side members and a series of cross members. The finished chassis has the appearance of a ladder.

Laden

Carrying a load.

Lag (Valve)

The term applied to valves which remain open after the piston has passed tdc or bdc at the end of a stroke in the four stroke cycle.

Lambda

Greek letter like an upside down y. It represents the ideal air to fuel ratio of 14.7:1.

Lambda Sensor

Provides information to the fuel system ECU on the oxygen content in the exhaust gas. Also, EGO Exhaust Gas Oxygen Sensor, HEGO Heated Exhaust Gas Oxygen Sensor and EOS Exhaust Oxygen Sensor.

Laminated

A layered component made from thin sheets of material.

Laminated Glass

Plastic or vinyl core with thin glass each side. An approved glass construction for vehicle windscreens.

Laminated Spring

A leaf spring with multiple leaves.

Land

The sliding areas on pistons either side of ring grooves or fluid passages. The area on shafts that an oil seal lip seals against.

Lap and Diagonal Belt

Type of seat belt that has a single belt threaded across the lap and shoulder and anchored at three points. The anchorage points are both sides of the lap and on the pillar above the shoulder of the wearer. Also known as a three point seat belt.

Lap Belt

Type of seat belt that has a lap restraint belt only.

Large Class 4

A Class 4 vehicle with a DGW greater than 2500kg.

Latching Relay

A relay that latches into a set position when first operated and then back to its rest position next time it is operated.

Latent Heat

The heat energy that is needed to bring about a change of state of a material. During a change of state the temperature remains constant.

Lateral Forces

Sideways forces.

Lateral Runout

Movement from side to side in a rotating component.

Laterally

Sideways to the length of the vehicle.

Latex

An emulsion; usually a dispersion of a polymer in water.

Layrub Joint

A type of limited angle constant velocity joint consisting of an enclosed rubber disc with two pairs of sleeves which are attached to mountings on the ends of the shafts.

Layshaft

The shaft in a manual gearbox carrying the gear cluster and meshing with the constant mesh gears. Also known as a countershaft.

Lazy Lock

Term used to describe the automatic closing of windows when central locking is operated.

lb. ft.

Pound Feet"

LC

Low Compression.

LCD

Liquid Crystal Display. An electronic display device using liquid crystals in a glass sandwich. The glass has an inner transparent series of conductors and polarizing filters. Electrical signals to the conductors rearranges the liquid crystals to form digital or other images.

Lead (Valve)

The term applied to valves which open before the piston has passed tdc or bdc at the beginning of a stroke in the four stroke cycle.

Lead Oxide

Material used for the positive plate material in a battery.

Leading Edge

The front edge of a brake shoe in relation to the direction of rotation of the brake drum.

Leading Shoe

A brake shoe that has a leading edge making first contact when applied. Also primary shoe.

Leaf Spring

Metal spring used on vehicle suspensions. Consists of one or more steel strips clamped together with a mounting eye at each end. The front eye is used for fixing to the chassis and the rear eye for fixing to a swinging shackle. Or it may have a mounting eye at the front and a flat end plate for a slipper shackle at the rear.

Lean Fuel/Air Mixture

A fuel/air mixture with a ratio less than the stoichiometric ratio of 14.7:1. A mixture strength with an excess of air and therefore oxygen.

Learning style

The way a person takes in, understands, expresses and remembers information; the way a person learns best.

Leather

A tough material produced from the skin of animals, by tanning or similar process.

LED

Light emitting diode. An electronic diode that emits light when an electrical current passes through it.

Legal Rights

Statutory rights within law.

Legislation

Laws.

Let-down Panel

Panel made by a paint technician with different methods of application and amounts of material, resulting in different shades of the same colour.

Levelling

The flowing out of a paint film, occurring from the time the paint particles form a wet film on the surface to the time the film hardens and dries.

Lever

A rigid rod or bar that moves about a fixed point.

Leverage

The use of levers to gain a mechanical advantage.

LHD

Left-Hand Drive

Libellous

Untrue and harmful information.

Library

Collection of materials i.e. books or cd's.

Lift Pump

A low pressure pump used to supply a carburettor or diesel injector pump with fuel. Driven mechanically from a cam in the engine or electrically from the battery.

Lifting

Attack by the solvent in a newly-applied paint on the substrate which results in distortion or wrinkling of the preceding dried or partially cured layers.

Light Meter

A meter that measures light intensity.

Lightness

The brightness of a paint or object compared to a perfect white. Measured by the amount of light reflected by a surface. A perfect white is one which reflects 100% of the light in the visible spectrum.

Limit Switch

A switch that operates by a linkage at the limit of its movement. For example, a wiper motor has a switch that operates when the blades are in the park position.

Limited Slip Differential

Final drive differential with a clutch or other device to limit the differential action when one wheel loses traction.

Limp Home

Electronic control systems on later vehicles can substitute faulty sensor signals and therefore a vehicle can 'limp home' even when a fault occurs.

LIN

The LIN-Bus (Local Interconnect Network) is a vehicle bus standard or computer networking bus-system used within current automotive network architectures. Local interconnect network (LIN) is a single-master, multiple-slave networking architecture originally developed for automotive sensor and actuator networking applications.

Linear

For an equal increase in one variable an equal increase occurs in another.

Linear Valve

A valve where the movement is proportional to the change in opening size.

Liner (Cylinder)

A steel sleeve used to form a running surface for pistons in an engine. Also known as a cylinder sleeve.

Lining

The friction material attached to brake pads, shoes and clutch friction plates.

Linkage

General term used to describe a collection of components that operate something.

Lip Seal

An oil seal with a lip that is reinforced with a coil spring and is used to retain oil on a revolving or reciprocating shaft.

Liquid Lever

Hydraulic cylinders that increase the force applied.

Little End

End of the con rod that fits to the piston.

Live Axle

An axle that transmits a drive to the wheels. Also known as a drive axle.

Live Feed

Electrical supply from (usually) the battery positive, possibly via the ignition switch and a fuse.

Load

Description of how hard an engine is working.

Load Carrying Member

A component of a chassis which carries or supports the weight of the vehicle, the engine or other mechanical system. Any other component that carries a load.

Load Sensing Valve

A valve in the rear brake circuit of a goods carrying vehicle that responds to the weight of load to vary the braking effort of the rear wheels.

Loading (Clogging)

The build-up of flatting residue between the abrasive particles on flatting papers or discs during use. Loading reduces the cutting effectiveness of the abrasive.

Lobe

The lever component of a cam set on an eccentric orbit from the centre axis of the shaft.

Lock (Steering)

The amount that the front wheels are able to turn from the straight ahead position to fully turned. Measures either as an angle of turn or the diameter of the minimum turning circle.

Lock Nut

A nut that is used to lock another nut or threaded component in position on a threaded rod or stud. Also jam nut - US term.

Lock Tab

Special washer that can be bent over to lock a nut or similar.

Lock-up Clutch

Automatically operated clutch in a torque converter applied during constant speeds to lock the input and output components together.

Logic Gate

A simple electronic device, which has an output that is dependent on its input of combinations of inputs. Common types are described as AND, OR and NOT.

Logic Probe

High resistance tester (so it does not load the circuit), that is used to check the logic state (1/0 or high/low voltage) of a circuit.

Longevity

Long life, long duration of service,durability

Longitudinal

Any axis running from the front to the rear of a vehicle or other object.

Longitudinal Axis

Any axis running from the front to the rear of a vehicle and parallel with the ground and the sides of the vehicle. The main vehicle axis runs through the centre of gravity of the vehicle.

Longitudinal Forces

Forces acting along the length of a vehicle.

Loom

The collection of vehicle cables wound together with an insulation tape. Also known as a 'wiring harness'.

LOS

Limited Operation Strategy. Get home or limp home mode of ECM when system failures occur.

Low Boilers

Solvents with low boiling points, usually less than 50 degrees Celsius.

Low Film Build

The condition of a paint film when it is too thin to provide protection to the substrate or withstand environmental conditions.

Low Profile Tyre

Tyre with an aspect ratio less than 80%. The depth of the tyre is less than the width by the percentage value.

Low Tension

The term used for the low voltage in the primary circuit of the ignition system.

Low Tension Circuit

The ignition coil primary or control circuit operating at battery voltage (low tension).

Lower Control Arm

The lower and longer wishbone in an independent suspension system.

Lower Quartile

Data is split into 4 equal quarters. The lowest quarter is referred to as the Lower Quartile. For example the Lower Quartile of 100 is the lowest 25 of the numbers.

LPG

Liquid Petroleum Gas.

LTFT

Long Term Fuel Trim

Lubricant

Oil, for example, to prevent surface contact.

Lubrication

Minimise friction with oil, grease, etc.

LUS

Lock-up solenoid. Operates with PCM signal to apply the torque converter lock-up clutch.

Lustre

Gloss or sheen of a finish.

LWB

Long Wheel-Base
M

M.O.T

Ministry of Transport. Colloquial for the annual inspection test for vehicles.

MAF

Mass Air Flow Meter.

Magnet

Any material with the naturally occurring phenomenon that has the ability to attract iron.

Magnetic field

Magnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges. The magnetic field at any given point is specified by both a direction and a magnitude (or strength).

Magnetic Flux

The force contained in a magnetic field.

Magnetic Pole

The ends of a magnet where the lines of force originate. The north and south poles.

Magnetic Pulse Generator

A sensor that uses an iron core and electrical winding to induce an electrical current when passed by a toothed wheel or rotor. Also known as an inductive generator.

Magnetic Stand

A holding device for measuring equipment such as a dial test indicator.

Magnetism

A natural force found in iron and some other materials.

Magnitude

The height of a wave. The maximum voltage in an AC wave pattern.

Main Beam

The upper of the two headlamp beams. Also driving beam and upper beam.

Main Bearings

Central journals and bearings on a crankshaft axis mounted in the engine crankcase. The crankshaft rotates in these bearings.

Main Gallery

A tube shaped section cast in to the engine block where other oil feeds are taken from.

Mainline Pressure

The regulated hydraulic pressure in an automatic transmission.

Makeup Air

A system that brings and heats air from the outside to a desired air flow and temperature.

Malleable

Describes a material that means it can be easily shaped.

MAM

Maximum Authorised Mass – The maximum gross weight permissible in GB.

Mandrels

Bars used to locate a component.

Manifold

Pipes or ducting to route air in or burnt gases out of an engine. Attached to the ports.

Manifold Absolute Pressure

The mean gas absolute static pressure in an engine induction manifold. Absolute pressure is equal to gauge pressure plus atmospheric pressure.

Manifold Vacuum

The depression or low pressure that occurs in the inlet manifold due to the increasing volume above the pistons when they are moving downwards in the cylinders. The airflow into a naturally aspirated engine cannot move quickly enough to fill the additional volume and therefore loses pressure and density.

Manual Transmission

Transmission system where the driver makes the gear shifts by means of a control (gear) lever and linkages to the gearbox.

Manual Valve

The gear selector valve in an automatic transmission operated by the driver.

MAP

Manifold Absolute Pressure Sensor. The mean gas absolute static pressure in an engine induction manifold.

Map Light

Small light used in a vehicle for illuminating a map!

MAP Sensor

A pressure sensor used to measure manifold absolute pressure in an engine induction system.

Mapping

Used to identify opportunities for developing and assessing key skills within the curriculum.

Mapping (Contouring)

Edge of a repaired area under a paint film that shows up after a surface has been repainted.

Masking

Application of paper or other material and adhesive tape to cover an object that must be protected from overspray.

Masking Paper

Paper designed to prevent paint from bleeding through.

Mass

The total theoretical weight of matter based on its atomic structure. The weight of matter without gravitational pull.

Mass Air Flow Meter

A sensing device in the air intake duct of a fuel injection engine that provides data for control of the quantity of fuel that is injected.

Master Cylinder

The pump on a brake hydraulic system.

MAT

Manifold Air Temperature

Matching

In painting, to make refinishing colours look the same as the original finish.

Matt

A surface with minimal reflection.

Matter

A term used to describe any substance as a 'quantity of atoms'.

Matting agent

An additive used to lower the gloss of topcoat, single-stage colours and clearcoats.

Mb

Megabyte. Used to measure computer memory. 1 Mb = 1,000,000 bytes or 1024 Kb (kilobytes).

MCM

Motor control module

McPherson Strut

Telescopic independently sprung suspension member incorporating a damper, and fixed at its upper end to the body. The lower end is located by linkages which counteract transverse and fore and aft movement. The original system used a track control arm for transverse forces and an anti-roll bar for longitudinal (fore and aft) location. Usually incorporated in a steered front suspension system.

MCS

Mixture Control Solenoid

MCT

Manifold Charge Temperature

Mean

The average value (the sum divided by the number of items).

Mechanical Advantage

The effectiveness of a simple machine, such as a lever, inclined plane, wedge, pulley system or a screw at amplifying a force.

Mechanical Efficiency

The ratio between the actual total output of a machine and the theoretical maximum output.

Mechatronics

A combination of a mechanical and electronic control system

Median

The middle number of a series when the data is arranged in ascending order.

Melamine

Used in 1K OEM finishes, a hard resin used to modify alkyd resins and other films formed used in baking finishes.

Memory

The stored data in a microcomputer or electronic control module.

Memory Chip

A chip that stores data.

Memory Keeper

A battery or secondary power source used to preserve ECU memories when the main battery is disconnected. It can often be plugged in to the cigar lighter socket.

Memory Saver

A battery or secondary power source used to preserve ECU memories when the main battery is disconnected. It can often be plugged in to the cigar lighter socket.

Mesh

Criss-cross fibres to produce a material with very small holes. Used to make filter elements.

Mesh (Gears)

Gear teeth in contact.

Metal Conditioner

An acid-type cleaner which removes small amounts of rust and corrosion left from mechanical metal cleaning. Usually based on Phosphoric Acid solutions.

Metallic Paint

Topcoat which contains metallic pigments, usually in the form of tiny flakes of aluminium. Custom finishes may use other non-ferrous metal flakes such as copper or bronze.

Metamerism

A term used to describe colours that match under a specific light source, but do not match under all light sources. It is primarily caused by the use of pigments that are different to those used in the original formulation.

Meter

Measuring the flow rate of a gas or liquid.

Metering

When applied to fuel systems a control device for achieving the correct air/fuel mixture strength for specific engine running conditions.

Metering Needle

See metering rod.

Metering Ports

Ports designed to a set size to allow accurate flow of fuel or air.

Metering Rod

A tapered needle in a jet in a carburettor. The taper allows a varied or metered supply dependent on the position of the taper in the jet.

Methanol

Methyl-alcohol used as a fuel or fuel additive.

Method

The way in which a task is carried out.

Methyl Ethyl Ketone (MEK)

A fast-evaporating solvent.

Metric

European standards of measurement based on the metre.

Metric Measurement

A system designed to regulate measurement. Each quantity has a single unit. These include; metre, kilogram, ampere.

MFI

Multiport fuel injection. Usually known a port fuel injection or multipoint fuel injection (MPI).

MH

Metal hydride

Micro Processor

A processor on a single integrated circuit or chip. The calculator in a microcomputer or electronic control module.

Micro Switch

A small switch usually operated by a moving mechanism.

Micro-checking

A condition which appears as severe dulling of a paint film, but when viewed under magnification, is actually very fine cracking of the painted surface .

Micro-porous

Containing lots of very small holes.

Microelectronics

Refers to integrated circuit electronics usually involving some form of processor.

Micrometer

Measuring device based on an accurate screw thread. Measurements can be taken to 0.01mm/0.001''.

Micron

A measure of paint film thickness, equal to one one-thousandth of a millimetre.

Microphone

A device that converts sound waves to audio signals.

Microsoft Office

A package of programs including Word Processor (Word), Spreadsheet (Excel), Presentation (PowerPoint), Email and Organisation (Outlook).

Microwave

1. Essential equipment for use when a technician is hungry...2. High frequency radio waves.

Middle Solvent

A solvent that evaporates at a medium rate, leaving the paint primarily during flash-off.

MIL

Malfunction indicator lamp. Dashboard warning light from an electronic control module to signal a system or component failure.

Milling

A machining process that uses a rotating blade to cut through the surface of materials.

Minibus

A motor vehicle constructed or adapted to carry more than eight but no more than sixteen seated passengers (see also Bus).

Ministry Plate

Displays the maximum authorised weights at which a vehicle may be operated. This information supersedes the maximum weights displayed on the Manufacturer’s plate.

Miscibility

The property of materials that mix easily.

Miscible

Capable of being mixed with or dissolved in other components of a paint, etc.

Misfire

Uneven running of an engine due to one or more cylinders not working properly.

Misrepresentation

Represent wrongly with false account (legal).

Mist Coating

A light sprayed coat of a paint material to assist in blending and/or gloss enhancement and metallic control in single-stage colours.

Mixing (Ratio) Stick

Instrument used to gauge the correct ratio of paint material being mixed for ready-to-spray configuration.

Mixing Ratio

The proportion of ingredients to be mixed together to make a ready-to-spray paint.

mm

Millimetres

Mode

The most common number in a series.

Modem

Modulator-demodulator. Used to convert computer signals so that they can be sent over telephone lines.

Modulating Valve

A valve that can be switched on and off rapidly such as to control its partially open position.

Modulator Assembly

Releases and re-applies fluid pressure to brake units. (ABS). Adjusts and regulates.

Modulator Valve

Flow control valve in power steering pump. In an automatic transmission a valve that responds to manifold vacuum to create hydraulic pressure feedback to the main control assembly.

Module

An electronic control unit for a vehicle system.

Mol

Method of Inspection

Molecular

Relating to atoms formed into molecules.

Molecular Mass

Term used to describe the mass of molecules - usually relating to the mass of the protons and neutrons.

Molecule

The smallest possible unit or amount of any substance which retains the characteristics of that substance.

Momentum

Force that keeps a body moving.

Monitor

The screen that displays information produced on a computer. An output device.

Monolith

The honeycomb catalyst support element in a catalytic converter.

Monopoint

A petrol fuel injection system using a single point (or monopoint) injector in a throttle body in the inlet air supply and positioned on top of the inlet manifold. Also throttle body injection (TBI).

Moonroof

See also Sunroof... A sunroof that has a clear glass panel, rather than being opaque, so that light can enter the vehicle even when the roof is closed. Some vehicle have a sunroof at the front and a moonroof at the back.

Moped

Three wheeled vehicle with max speed of 45km/h, not over 50cc for a petrol engine or 4KW for any other engine or electric motor, not more than 450kg ULW.

MOST

Media Oriented Systems Transport. This protocol defines a multimedia fibre-optic point-to-point network implemented in a ring, star or daisy-chain topology over Plastic optical fibres. The MOST bus specifications define the Physical Layer as well as the Application Layer, Network Layer, and Medium Access Control. The MOST bus provides an optical solution for automotive media networks.

MOT

Ministry of transport (UK)

Motor Reverse Circuit

An electrical circuit that reverses polarity supplied to a motor.

Motor tricycle

Three wheeled vehicle with wheels symmetrically arranged, a max speed over 45km/h, or engine size over 50cc.

Mottling

A film defect appearing as blotches or surface imperfections, normally due to metallic or pearlescent pigments not being properly orientated in the paint film.

Mould-Release Agents

Chemical compounds applied to manufacturing moulds which must be removed by a pre-treatment prior to refinishing plastic parts to insure adhesion.

Mounting

General term for the part of a component, or a separate component, which fits one thing to another.

Mounting Studs

Threaded fixings for an exhaust flange or similar.

Mountings

Insulated or solid attachments for components/units on the vehicle. Insulated versions absorb vibration and provide some protection from shock loads.

Mouse

An input device that allows the user to move the pointer around the screen and click on different items to operate computer applications.

Moving Conductor

The armature in a motor or dynamo.

MPFI

Multi Point Fuel Injection

MPG

Miles Per Gallon

MPH

Miles Per Hour

MPI

Multipoint Fuel Injection.

MPV

Multi-Purpose Vehicle

ms

Millisecond

MSDS

Material Safety Data Sheets.

Muffler (Silencer)

A component in the exhaust system to absorb the gas shock waves and noise in order to reduce the emitted noise from a vehicle engine. Also known as a silencer.

Multi-Plate Brake

A brake that uses several clutch-type plates.

Multi-plate Clutch

A clutch mechanism having a series of friction and steel plates in a clutch drum assembly. One set of plates is splined to the drum and the other to a centre shaft so that drive through the clutch is via the drum, friction faces and the centre shaft.

Multi-vee Belt

A flat drive belt with several ridges or vee shapes running circumferentially (the long way round).

Multigrade Oil

Classification for lubricating oils that change viscosity grades during temperature change. The lower number is the cold temperature grade and the higher number the hot temperature grade. These oils do not thin at the same rate as single grade viscosity oils as the temperature rises. Also known as multiviscosity oils.

Multimeter

An electrical measuring tool with functions for volts, amps and ohms.

Multiplate

A clutch mechanism having a series of friction and steel plates in a clutch drum assembly. One set of plates is splined to the drum and the other to a centre shaft so that drive through the clutch is via the drum, friction faces and the centre shaft.

Multiplexed

In signal transmission where each set of signal pulses is given a certain time or frequency slot. This allows a great number of individual signals to be carried by a common conductor.

Multiplexer

A unit used for signal transmission where each set of signal pulses is given a certain time or frequency slot. This allows a great number of individual signals to be carried by a common conductor.

Multiplexing

A common conductor system for digital signal transmission where each set of signal pulses carries its own unique identity. This allows a great number of individual signals to be carried by the common conductor.

Multiplug

A connector with more than one electrical terminal inside.

Multipoint Fuel Injection

Gasoline electronic fuel injection system with injectors in each inlet manifold spraying fuel in towards the inlet valves in the ports of each cylinder. Also known as port injection.

Multisockets

Sockets with many positions for fitting over a bolt or nut head. Sometimes described as multihex.

Mutual Induction

The electrical current induced in one conductor because of the electrical current flow and magnetic field produced around another conductor nearby. Used in transformers to induce a current in one winding from the electrical flow of another when both are wound around an iron core to create a magnet field.

mV

Millivolts
N

Nave

Part of a wheel: connects the rim to wheel hub.

Navigation

The way in which you get around a program or website.

NDS

Neutral Drive Switch.

Needle Bearing

A bearing made from small diameter rollers in between inner and outer bearing tracks.

Needle Valve

(1) Valve by which fluid flow rate is controlled by the degree of insertion of a tapered needle into a fixed diameter orifice. This type of valve can provide a fine gradation of flow. (2) Valve in which a blunt, conically ended needle seats on a fixed diameter orifice. With this type of valve there is little or no gradation of flow, control being limited to full, with needle lifted, or none, with needle seated.

Negative Camber

Steering geometry where the road wheel leans inward at the top.

Negative Castor

Angle in side elevation between the steering and vertical axis. Steering axis hits the ground behind the vertical axis.

Negative Communication

A comment or statement expressing lack of approval.

Negative Offset (Wheel)

The position of the wheel nave or disc when inside the centre line of the wheel.

Negative Scrub

Negative scrub radius steering geometry where a line through the steering swivel axis meets the road surface outside of the tyre centre line.

Negative Temperature Coeffcient

See Negative Temperature Coefficient.

Negative Temperature Coefficient

Type of resistor that has resistance reducing with increases in temperature. These resistors are used in electrical circuits to give temperature sensing and control. Thermistor.

Negative Temperature Coeficient

See Negative Temperature Coefficient.

Network

Interlinked group of computers so that resources can be shared.

Network Card

A piece of hardware that allows computers to be connected to a network.

Neutral

Gearbox position when no gear is selected and no drive transmitted.

Neutral Drive Switch

On a transmission system, a switch that makes when neutral is selected.

Neutral Steer

Steering condition when the vehicle follows a true line in relation to the steered wheels.

Neutron

One of a number of particles in the nucleus of an atom. The neutron has no polarity and is electrically neutral.

New and like-new finishes

Finishes that have maintained a brilliant, high-gloss performance.

Newton (N)

A standard unit of force.

Ni(OH)2

Nickel di-hydroxide

NiMH

Nickel metal hydride – used in alkaline batteries.

NiOOH

Nickel hydroxide

Nip (Bearing)

The amount by which shell bearing halves are clamped in order to secure them in their housing.

Nm

Newton Metres

Non Independent

Describes suspension systems using a solid beam axle where the movement of one wheel affects the other wheel on the same axle.

Non-ferrous

Describes metals which contain no iron.

Non-metallic

Used to describe paint finishes that do not contain metallic pigments, i.e. Solid colours

Non-porous

Prevents flow or holds back a liquid.

Non-Return Valve

A valve that will allow fluid or gas to pass in one direction only.

Non-Verbal

Any form of communication that does not use words, i.e. traffic lights, shaking somebody's hand and smiling.

Normally Aspirated

Non pressure-charged engine using atmospheric pressure and cylinder vacuum to charge the cylinders.

North Pole

The term used to describe one of the poles of a magnet where the magnetic field lines of force start.

NOx

Oxides of nitrogen. An exhaust emission pollutant.

Nozzle

The tip of an injector from where the fuel is sprayed.

NT

Nominated Tester – a person nominated by an AE to carry out tests, Inspectors appointed by Designated Councils to carry out tests, all of which are approved by VOSA. Also VOSA staff appointed under section 66A of the Road Traffic Act 1988.

NTC Resistor

Type of resistor that has resistance reducing with increases in temperature. Used for temperature sensors.

Nucleus

The mass of neutrons and protons at the centre of an atom.

NVRAM

Non-volatile Random Access Memory
O

O Rings

Circular rubber rings used to seal pipe and other connections.

O2

Oxygen

O2 Sensor

Oxygen sensor, lambda EGO or HEGO sensor to provide exhaust oxygen content signal to the ECM.

O2S

Oxygen Sensor

OBD

On board diagnostic. A connector for diagnostic analysis of a vehicle's electronic systems.

OBD I

Onboard Diagnostics One

OBD II

Onboard Diagnostics Two

Objective

The goal intended to be attained and which is believed to be attainable.

Objective Information

Information that is unbiased and open minded.

Obligatory

Compulsory.

Obscene

Offensive, foul, disgusting.

OC

Oxidation Catalyst.

Occupation

The job that you do. For example, training to be a motor mechanic is training for an occupation.

Octane Rating

The anti-knock property of petrol fuel. The octane rating or number is a comparison against two standard fuels, heptane and iso-octane having values of zero and 100 respectively. Most road vehicles use petrol with octane ratings between 93 and 98.

OD

Outside Diameter

Odometer

Instrument that displays distance travelled by vehicle.

OE

Original Equipment

OEM

Original Equipment Manufacturer.

Offensive

To attack somebody/something.

Office Applications

A package of programs including Word Processor (Word), Spreadsheet (Excel), Presentation (PowerPoint), Email and Organisation (Outlook).

Offset

Any point that is not on the axis of shaft or component.

OHC

Overhead cam - type of valve operating gear. Camshaft in cylinder head above the valves.

Ohm

Electrical unit of resistance.

Ohm's Law

The electrical law, named after its originator, that shows the relationship between electrical pressure in volts, electrical current in amps and the electrical resistance in Ohms is proportional. Volts is equal to amps multiplied by Ohms.

Ohmmeter

A meter for measuring Ohms, the standard unit for electrical resistance.

OHV

Overhead valve - type of valve operating gear. Camshaft in cylinder block connected to valves by push rods and rockers.

Oil Cooler

A small heat exchanged (radiator), which has oil pumped through so that a flow of air will cool it.

Oil Dilution

The thinning of engine oil by fuel flowing down the cylinder walls into the oil pan.

Oil Drillings

Holes through various engine components, such as the crank, to allow oil to flow.

Oil Pan

Sump that holds oil for lubricating the engine.

Oil Pump

An mechanically driven pump used to supply oil pressure.

Oil Seal

A seal that prevents oil loss. Usually described as a radial lip seal but other types are used.

Oil Separator

Plates or baffles used to prevent oil being mixed with air or drawn through air pipes.

Oil Strainer

The mesh filter on the end of an oil pick up pipe.

Oil-Based Paints

Paints which dry by absorbing oxygen from the atmosphere. This 'uptake of oxygen' promotes a chemical reaction which is irreversible.

On Board Diagnostics (OBD)

See OBD

One-way Clutch

An automatic mechanical clutch that permits drive from one shaft to another in one direction only. A drive transmitted to the outer hub of the clutch bypasses the inner hub and the clutch free wheels. This type of clutch allows drive to be transmitted by two alternative routes and at different rotational speeds.

Opacimeter

Smoke meter used to measure the amount of smoke in diesel engine exhaust gases.

Opacity

The ability of a paint film to obliterate the colour or pattern of a surface. Opacity is measured by determining the minimum thickness at which a paint film will completely obscure a black and white pattern.

Opaque

Impervious to light transmission -non-transparent.

Open Circuit

Applied to an electrical circuit when the switch is 'off' or the circuit is not continuous.

Open Coat

A type of abrasive paper coating in which the abrasive particles are scattered in a low density to prevent it from clogging up. Typically found in Production Papers

Open Period

(1) The number of degrees of distributor rotation during which the primary circuit remains open. (2) The number of degrees of crankshaft rotation during which an inlet or exhaust valve remains open.

Open-loop

An electronic control system using a comparison of sensor signals and a pre-programmed map.

Operational Safety

Safety aspects that are operational during use of a vehicle.

Optical Gauge

A measuring instrument that uses light/reflection to align steering (for example).

OPTL

One Person Test Lane. These are lanes authorised by VOSA to conduct testing where the tester has the option of not using an assistant if so desired.

Orange cables

These indicate high voltages – take care.

Orange Peel

An irregularity in the surface of a paint film resulting from the inability of the wet film to "level out" after being applied, caused by a lack of flow. Orange peel appears as a characteristically uneven or dimpled surface to the eye, but usually feels smooth to the touch.

Orbital Sander

Type of sander that uses a circular motion to accomplish the sanding of different materials.

Organic Materials

Compounds composed of carbon, hydrogen, and other elements with chain or ring structures.

Orifice

A hole, usually with a precise drilling diameter to control a fluid flow or spray.

OS

Oxygen Sensor

Oscillate

To move or swing from one place to another (e.g. side to side).

Oscillator

An electronic circuit that produces as signal of a set frequency.

Oscilloscope

Also shortened to ‘scope'. An instrument that draws an image to represent changes in voltage over a set time period.

Otto Cycle

An alternative term for the four stroke engine cycle using the name of its inventor.

Out-of-round

A term used to describe a component that should be perfectly round or cylindrical but is not. Usually caused by wear but can be from faulty machining.

Outdoor Exposure

The most realistic way to measure the behaviour of a paint film. Manufacturers paint sample panels and leave them exposed to the elements for long periods of time, and inspect them at intervals to measure the effects of the exposure.

Outer Races

The outside rings of ball or roller bearings.

Outgoing Telephone Call

To make a telephone call to somebody.

Outlet Ports

Used to describe any port that allows a gas or liquid to leave. Exhaust ports are a good example.

Output

Power or data that comes out from a mechanical unit or electronic control module. Usually adapted or modified by the unit or module to suit a particular purpose.

Output Circuit

The battery charging circuit for the electrical current from a generator.

Output Device

A device that allows information from the computer to be displayed. Egg, monitor, printer.

Output Shaft

Shaft that outputs drive from a gearbox to a propshaft or final drive.

Oven

Equipment used to bake paint finishes. Originally developed by vehicle manufacturers, whose applied finishes may require temperatures as high as 180°C to cure. In the refinishing industry, ovens are used to bake sprayed coatings at varying temperatures up to 80°C, producing fully-cured finishes in as little as 20 minutes.

Over-thin

To add more thinner or reducer to a paint than is normally necessary for application. This is sometimes done in order to lower the paint viscosity, to aid in blending, or to achieve a special colour effect with metallics or pearlescents

Overall Painting

A type of refinish task in which the entire car is completely repainted.

Overall Ratio

The term used to describe the output ratio of a series of mechanical components such as gears or levers.

Overbake

The result of curing a paint film at too high temperature, or for longer than the specified time. The film often becomes too hard and brittle.

Overdrive Gear

A gear drive that increases the rotational speed of the output shaft above that of the input shaft.

Overdrive Unit

A separate unit that at one time was fitted on the output shaft of a gearbox. It produces a higher gear ratio.

Overlap

The area of coverage in which one spray pass is extended over and partly covered by the next pass.

Overlap (Valve)

The term used to describe the angle of crankshaft rotation when the inlet and exhaust valves are both open.

Overrun

Movement of vehicle when engine is not under power. Engine braking.

Overrun Clutch

(1) A clutch on a starter drive pinion that prevents the engine from driving the starter motor after the engine has started. (2) A one-way clutch in an automatic transmission.

Overspray

An overlap of dry spray particles landing on areas that were not meant to be painted, or on previously painted areas where they do not blend in.

Oversteer

Steering condition of a turning vehicle when the vehicle attempts to turn by a greater degree than the steered position taken by the driver. A difficult driving condition requiring opposite lock to control.

Oxidation

The chemical combination of oxygen and the binder of synthetic-enamel type paints which leads to drying. Also refers to the destructive combination of oxygen with a dry paint film leading to age degradation, or the destructive combination of oxygen and metal commonly known as Corrosion.

Oxygenated Solvent

An organic solvent containing oxygen as part of the molecular structure. Alcohols and ketones are oxygenated compounds often used as paint solvents.

Ozone

A colourless gas (O3) soluble in alkalis and cold water; a strong oxidizing agent; can be produced by electric discharge in oxygen or by the action of ultraviolet radiation on oxygen in the stratosphere (where it acts as a screen for ultraviolet radiation).
P

P/B

Power Bakes

P/N

Park and neutral position switch for sending signals to the PCM.

P/S

Power Steering Pressure Switch. Also PSP switch.

PA

Pressure Air

Pace

The relative speed of progress or change.

Paint

A material which, when applied as a liquid to a surface, forms a solid film for the purpose of decoration and/or protection. Generally, any paint contains a binder, solvent, and pigment plus other chemicals or additives giving the paint its special characteristics or properties.

Paint Remover

A chemical, usually a mixture of acid and solvents that breaks down an old paint finish by liquefying it, thus allowing it to be completely removed from the substrate.

Paint Strainer

A disposable fine mesh filter used to clean paint as it is poured into the gun cup.

Paint thickness gauge

Precision instruments to accurately measure the dried film thickness of painted objects by non-destructive testing. On ferrous substrates, they operate by measuring the resistance to the flow of magnetism between two probes, and on non-ferrous surfaces special gauges use the 'Eddy Current' principle

PAIR

Pulsed Secondary Air Injection

Pan

Alternative name for a sump.

Panel Lights

Illumination for instruments and other displays.

Panhard Rod

Rear axle transverse link between the chassis and axle beam. It is used to hold the axle in relation to the body during cornering or for sideways forces.

Paraffin

A petroleum based thin and colourless fuel oil, (kerosene in US English).

Parallel

The condition that exists when the centre lines of two or more items or components or lines do not converge. The extended lines in both directions will always remain at an equal distance apart.

Parallel circuit

A circuit that splits into two or more branches. A break in one will not stop current flowing in the other(s).

Parallel hybrid

The engine and motor can both be used to drive the vehicle (most hybrid vehicles use this system).

Parasitic draw

An unwanted, usually small, current flow from a battery.

Parking Brake

Mechanical system of braking to hold vehicle stationary.

Parking Gear

The component(s) in an automatic box that lock the drive when 'Park' is selected.

Particle Size

The size of the pigment particles in a dispersion (e.g. paint).

Particulates

Exhaust pollution consisting of very small particles of matter (soot) that are produced as a by-product of combustion. Seen as smoke in a vehicle exhaust, particularly from diesel engines.

PAS

Power Assisted Steering.

Pascal (Pa)

Standard unit of pressure (N/m2) named after a scientist who studied pressure in liquids. Pascal's principle of the transmission of pressure in fluids established that the pressure in a completely filled container is equally applied throughout and any change in pressure is transferred to all parts of the fluid and walls of the container.

Passivation

The conversion of a metal surface to a less reactive state. A process used by vehicle body manufacturers to reduce the corrosion rate of a metal surface, particularly low-carbon steel.

Passive Restraint

Safety features of a vehicle that act only in an accident. Seat belts, head restraints, air bags and pre-tensioners are examples.

Password

Personal Identification, used in conjunction with a Smart Card to access the MOT database via the VTS device. Can be numbers or letters, or a combination of both.

Pawl

Part of the ratchet mechanism that holds the ratchet. A pivoted tooth that engages in the teeth of the ratchet wheel to either prevent the pawl lever or the wheel from rotating in one direction only or in some mechanisms to drive the wheel forward.

PCM

Powertrain Control Module.

PCV

Positive Crankcase Ventilation. A series of pipes and valves connecting the engine crankcase to the inlet manifold or air cleaner in order to reduce oil vapour emission to atmosphere.

PDU

Power drive unit

Pearls (Pearlescents)

Finishes which include mica flakes in addition to the pigment and binder. These finishes are highly decorative and often give the impression that the colour alters as the viewing angle is changed.

PECV

Power Enrichment Control Valve

Peeling

The failure of a paint film to adhere to its substrate. Peeling results when contaminated surfaces are painted, when there is an excessive difference between paint and surface polarity or thermal expansion, or when there is solvent incompatibility.

Pentagon

The Pentagon, is a government building with five sides that serves as the headquarters of the United States Department of Defence. A pentagon, is a five sided shape.

Percent

The proportion of one part of something to the whole. Usually out of 100 (‘per' means ‘out of' and ‘cent' means ‘hundred').

Percentage Change

Changed amounts divided by the original value, then multiplied by 100.

Perceptual Safety

A reference to how safe the driver and passengers feel.

Perimeter

The sum of all the outside edges of a shape.

Perishing

Description of how some components, particularly if rubber-based, can decay.

Perpendicular

At ninety degrees to another plane or line.

Petrol

Volatile hydrocarbon fuel for spark ignition engines. Also gasoline.

Petroleum Jelly

A type of grease used for battery terminals. Vaseline is a refined version.

Pferdestärke

The German word for horsepower. Pferdestärke. 1PS equals 0.986bhp.

PFI

Port Fuel Injection.

PG

Pulse Generator.

PH value

A measure of the acidity of a substance in an aqueous solution. Pure water has a pH value of 7 and is classified as neutral. Below 7 is acid and above 7 is known as basic. The scale is from 0 (strong acid) to 14 (strong base).

Phase

The time span between the start and end of a single wave moving from zero to positive and negative positions and returning to zero.

Phase Sensor

Sensor that indicates camshaft position and hence where the engine is in its cycle.

Phasing (diesel injection)

There are a number of phases of injection: fill phase, spill phase, injection phase and the pressure reduction phase.

Phosfor Bronze

See Phosphor Bronze.

Phosphating

A process used by vehicle body manufacturers which results in the formation of a layer of zinc, iron, or manganese phosphate crystals on the surface of the part to be painted. In modern vehicle construction plants, phosphating is achieved by complete body immersion.

Phosphor bronze

A material that can absorb oil making it ideal for making bushes/bearings.

Phosphoric Acid

An acid commonly used as a catalyst to speed up the cure of Etch primers and some baking finishes, usually alkyd/nitrogen resin combinations. Also a cleaner used for removing surface corrosion from ferrous metals.

Photoelectric

The generation of an electrical current by light shining on certain materials such as some semiconductor devices. Photoelectric cell, photodiode or phototransistor.

Phototransistor

A transistor that is operated by light.

Phrase

A group of words in sequence.

Physical layer

Hardware, actual components and wires as opposed to software.

Pi

3.141592 (3.142).

Pick Up Pipe

Oil pipe that picks up oil from the oil pan.

Pickling

The use of a chemical solution (usually acidic) to prepare a surface for painting or bonding by dissolving away surface oxides and other impurities.

PID

Parameter ID

Piezo-resistive

A special crystal that changes resistance as pressure is applied.

Piezoelectric

Voltage produced by shock waves on a piezo crystal. Used in engine knock sensors.

Pigment

Small particles added to paint to influence properties such as colour, corrosion resistance, mechanical strength, etc. Pigments may be coloured, semi-transparent, black, white, or colourless. They must be incorporated into a paint system by very efficient dispersion processes.

Pilot Bearing

Small bearing usually where two shafts meet. See also Spigot.

Pinging

Noise heard from an engine when the ignition of fuel occurs too early (advanced) in the cycle. Also 'ping'.

Pinholing

A defect consisting of tiny holes in the dried paint surface. Defects such as pin holing, popping, bubbling, and cratering are usually caused by solvent vapours forming from the substrate or the paint and rising to the surface.

Pinion

A small gear wheel or the driver of a meshing pair of gear wheels.

Pinion Gear

A small gear wheel or the driver of a meshing pair of gear wheels.

Pinion Shaft

A shaft on which a small gear runs.

Pinking

Noise heard from an engine when the ignition of fuel occurs too early (advanced) in the cycle. Also 'ping'.

Pintaux

Type of injector for an indirect injection engine. Similar to pintle but with additional small injection orifice for low engine speeds.

Pintle

Type of injector for an indirect injection engine. Uses a spring-loaded needle that is raised by fuel pressure to allow a spray of fuel to enter the pre-combustion chamber.

PIP

Profile Ignition Pick Up Signal.

Pipe Union

A joint in a pipe.

Piston

Reciprocating component, usually in the form of a cylinder closed at one end, that operates under fluid pressure within a smooth walled cylinder. In a reciprocating engine, gas pressure on the piston crown provides the prime force that is converted into rotating mechanical power by the crankshaft.

Piston Blow

Term used to describe gases blowing past the piston rings.

Piston Crown

The top of the piston.

Piston Ring

Sealing rings usually made of cast iron. Fitted on to a piston to make a gas tight seal.

Pitch

(1) Distance that two points are apart. Examples are thread dimensions and pitch circle diameters of concentric drillings. (2) Vehicle body movement from back to front or from front to back.

Pitman Arm

The output arm on a steering gearbox. Also known as a drop arm.

Pitting

The appearance of holes or pits in a paint film while it is wet. May also refer to the damage caused by more serious rusting on steel panelwork

Pivot Bolt

A simple bolt on which something pivots (turns).

Pivot Point

The point about which something pivots!

Planet Carrier

Frame with spindles that the planet gears rotate on as part of an epicyclic gear set.

Planetary Gears

Gears that rotate around sun gears (differential, epicyclic gearing, etc.)

Planning

The act of forming and following a program to achieve a specific goal.

Planometer

A flat metal plate for gauging the accuracy of a plane surface in precision metalworking, which is also known as a surface plate

Plastic Filler

A compound of resin and heavy pigments used to fill dents on car bodies.

Plasticizer

A low molecular weight substance added to polymeric materials such as paints to improve their flexibility.

Plastigauge

Brand name of a product that is used to determine bearing clearance.

Plate Grids

Basket like holders to contain the active material in a battery.

Plate Lug

A connection point on the battery plate.

Plenum

A chamber in the air inlet system to provide even air supply to all cylinders.

Plies

Rayon cords used in tyre construction.

Plug Thread

Screwed thread that is designed for a spark plug.

Plunge Joint

A shaft joint or coupling with provision for axial or plunging movement.

Plunger

Alternative term for a piston or needle in a pump, slave cylinder or injector.

Ply (Tire)

Fabric layer used in the construction of a tire.

Ply (Tyre)

Fabric layer used in the construction of a tyre.

Ply Rating

Load rating of a tyre.

Pneumatic

Transfer of force by air or gas.

Pneumatic Suspension

Suspension system using air or gas springs.

PNP

Park/Neutral Switch

Podger

A tool in the form of a short bar, usually tapered and often incorporating a spanner/wrench at one end.

Points

The switching contacts of an ignition contact breaker.

Polarised Light

Light that has been filtered so that its rays oscillate only in one direction.

Polarity

A description of a component that must have positive and negative connections connected correctly.

Polarity (Electrical)

Electrical positive and negative charges.

Polarity (Magnetic)

Magnetic north and south poles.

Polarized Light

Light that has been filtered so that its rays oscillate only in one direction.

Pole

The ends of a magnet where the field lines are emitted.

Polish

A specially formulated blend of components designed to remove minor paint surface imperfections, such as fine scratches, light oxidation, water spots, and swirl marks left by the use of rubbing compounds.

Polishing

The use of polishes, either by hand or machine, to level and provide more gloss to a finish.

Polishing Compound

A mild abrasive material applied to a vehicle's painted surface which removes minor imperfections with minimal cutting action. Buffing restores film to a high gloss appearance.

Polishing Wax

A combination of wax and polish that contains mild abrasives. The abrasives remove minor paint imperfections. The wax and other ingredients produce a durable, high-gloss finish.

Pollution

Products or by-products that destroy purity or make environments foul or filthy.

Polyester

A 2K resin used as the binder for plastic fillers, fibre glass laminations and high-build primers

Polyester Stopper

A finer grade 2K plastic filler material used to fill minor imperfections such as pinholes in filler prior to priming.

Polymers

A naturally occurring or synthetic compound consisting of large molecules. Used for many purposes, one of which is as a polish.

Polypropylene

Manmade plastic material used for electrical insulation, bumpers and other trim components.

Polyurethane

A 1K or 2K plastic-based paint finish that is characterised by durability and high gloss. Also, used for manufacturing some plastic and flexible parts.

Poppet Valve

Conventional inlet and exhaust valves having a circular plate at right angles to a central stem that runs through a guide tube.

Popping

A paint defect characterized by raised domes in the surface caused by solvent vapour forming within the paint after it has begun to "skin over." Often caused by baking at too high a temperature or before adequate flash-off time has been allowed.

Population of UK

Number of people that live in the UK.

Porosity

Property of a material that allows fluid to soak into or through it.

Port

Hole or aperture shaped to facilitate the flow of gas or liquid into or from a chamber. Usually denoted by its function, as inlet port or exhaust port.

Port Fuel Injection

Petrol electronic fuel injection system with injectors in each inlet manifold spraying fuel in towards the inlet valves in the ports of each cylinder. Also known as multipoint injection.

Portfolio

This is usually a folder that contains the evidence chosen to illustrate competence to satisfy individual key skills requirements.

Position Switch

A switch used to feedback position of a moving component.

Positive Camber

Steering geometry where the road wheel leans outward at the top.

Positive Castor

Angle in side elevation between the steering and vertical axis. Steering axis hits the ground in front of the vertical axis.

Positive Communication

A comment or statement expressing approval.

Positive Crankcase Ventilation

A series of pipes and valves connecting the engine crankcase to the inlet manifold or air cleaner in order to reduce oil vapour emission to atmosphere.

Positive Displacement

A term applied to pumps which transfer liquid in the same quantity as the volume in the pumping chamber for each action of the pump.

Positive Offset (Wheel)

The position of the wheel nave or disc when outside the centre line of the wheel.

Positive Scrub

Positive scrub radius steering geometry where a line through the steering swivel axis meets the road surface inside of the tyre centre line.

Positive Temperature Coefficient

Type of resistor that has resistance increasing with increases in temperature. The normal response for metal conductors. These resistors are used in electrical circuits to give temperature sensing and control.

Potential

Energy stored in a stationary object or chemical combination that has the capacity to do work.

Potential Difference

Difference of electric potential between points (pd) volts.

Potentiometer

A variable resistor with manual operation that provides an output voltage from a sliding terminal on a resistor block.

Pounds Feet

Old unit of torque. Also foot pounds. Torque is now given in the SI units of Newton metres Nm.

Pour Point

Applied to fuel oils (diesel) to indicate the temperature where it will still flow under its own weight. The pour point specified value is 3 degrees above the point where it will only just flow.

Powder Coatings

Any protective coating which is applied to the surface as a dry, finely ground powder and then carefully heated above its melting point so that the powder particles flow together to form a continuous film.

Power

The rate of doing work. It is measured by the standard unit called the watt (W) and is equal to one joule per second. This is a very small unit and kilowatt (kW) or megawatt (MW) is more often used. Also, Horsepower which is the old term for power.

Power Assisted Steering

The use of a hydraulic or electrical system to increase the driver's effort on the steering wheel thus reducing the effort that the driver has to apply.

Power Booster

Hydraulic or pneumatic brake pedal or hydraulic pressure booster.

Power Distribution

A central point from which various components are supplied.

Power Output

Power developed by an engine.

Power split hybrid

A combination of a series and parallel hybrid that uses a mechanical splitting device.

Power Stroke

Part of the four-stroke cycle following combustion.

Powertrain

Term used to describe the engine, transmission and driveline components as a unit.

PPE

Personal protective equipment

PPM

Parts Per Million

Pre-ignition

Spontaneous ignition in a petrol engine that occurs before the controlled ignition point. Can be caused by an overheated engine, incandescent particles in the combustion chamber or incorrect fuel.

Preignition

Spontaneous ignition in a petrol engine that occurs before the controlled ignition point. Can be caused by an overheated engine, incandescent particles in the combustion chamber or incorrect fuel.

Preload

Additional tightening of a bearing or component after the backlash or free play has been eliminated. Used to eliminate backlash after the bearings have bedded in. Usually set by a Nm or angular torque.

Presentation

The way in which something is displayed.

Pressure

Pressure is the product of a force multiplied by the area on which the force is applied. The standard unit of pressure is the Pascal which is equivalent to one N/m2.

Pressure Bleeder

A brake/clutch bleeder that forces fluid through the system.

Pressure Cap

Cap used to pressurise cooling system.

Pressure Chamber

An area used to hold a pressure as something expands of to supply pressure.

Pressure Charged

An engine using a pressure-charger to boost the air charging pressure above atmospheric pressure, to increase the air mass entering the cylinders of the engine.

Pressure Conscious

Variable opening valve used for sensing and adjusting the pressure in brake circuits to restrict force to the rear brakes.

Pressure Differential

The difference in pressures between two sides of a component or areas in a system that are used to operate the component or system. Atmospheric pressure is often used in conjunction with a vacuum to provide a force.

Pressure Gauge

An instrument for measuring pressure of a fluid or a gas.

Pressure Modulator

A device for controlling pressure in a system.

Pressure Plate

Component of the clutch.

Pressure Regulator

A valve in a hydraulic system that controls line pressure.

Pressure Relief Valve

The valve in an oil or hydraulic circuit that opens to release excess fluid pressure and return fluid to the feed side of the pump.

Pressure Switch

A pressure sensitive switch used to provide a signal voltage to an instrument, lamp or electronic control module.

Pressure Wave Supercharger

A supercharger using the exhaust pressure waves to boost the inlet air pressure. This supercharger uses a drum with longitudinal drillings that is rotated in time with the engine and ported to match inlet and exhaust pressure waves together.

Pressure-feed Gun

A spray gun equipped with a separate paint container that is pressurized and connected to the spray gun by means of a solvent-resistant fluid hose, in addition to the normal air hose.

Primary Shoe

A brake shoe that has a leading edge making first contact when applied. Also leading shoe.

Primary Winding

The low tension (primary circuit) coil of wire in an ignition coil.

Primer

The first coat of paint applied to a substrate. Depending on the formulation of a particular primer, its function can be to provide any combination of">adhesion, build, scratch-filling, ground coating and corrosion resistance.

Primer-sealer

An undercoat which improves adhesion of the topcoat, by sealing off old painted surfaces that have been sanded; usually does not require sanding when dry.

Priming

Lifting fuel into the system components to remove air.

Priming Pump

A manually operated pump that lifts fuel into the system.

Printer

An output device that allows data from the computer to be displayed on paper.

Processor

The central processing unit oversees all of the other components of the system. Can be thought of as the brain of the computer.

Progression

Initial acceleration of the throttle after the idle position. Going onward/upward.

Progressive Carburettor

Usually a carburettor with two chokes, the second of which only opens as the throttle is pushed further down.

PROM

Programmable Read Only Memory.

Propeller Shaft

Connects gearbox to final drive and transmits torque on rear wheel and four wheel drive vehicles.

Propellor Shaft

See Propeller Shaft.

Proportion

The relation of one thing to another.

Proportioner Valve

A valve used in hydraulic brake circuits to split the force between the front and rear brake circuits.

Propshaft

Connects gearbox to final drive and transmits torque on rear wheel and four wheel drive vehicles.

Propshaft Joints

Universal joints used to allow a propshaft to work through an angle.

Propulsion

Application of a driving force.

Proton

One of a number of particles in the nucleus of an atom. The proton has a positive polarity and is electrically positive in opposition to the negative charge of the electrons.

Prototype

A working version of a new design.

Provenance

The origins of information.

PS

The German word for horsepower. Pferdestärke. 1PS equals 0.986bhp.

Psi

Pound per square inch. A measure of pressure in old units. The SI unit of pressure is the Pascal (Pa).

PSP

Power Steering Pressure

PSPS

Power Steering Pressure Switch.

PT

Part Throttle.

PTC

Pending Trouble Code

PTO - Power Take Off

A supplementary drive from a vehicle transmission that is used to drive to auxiliary units.

Pull-in Winding

A winding in a starter motor solenoid that actuates the solenoid to pull the switch contacts together. It is often earthed through the armature so that the drive pinion rotates as it moves into mesh with starter ring gear.

Pull-off Spring

A simple return spring to open or close something after it is switched off.

Puller

A tool for applying a pulling force. For example, to remove a gear from a shaft.

Pulleys

Used to transmit or receive drive from a belt. The alternator pulley is a good example.

Pulsation

On/off or increase/decrease in pressure or position.

Pulsation Damper

Any device, such as a hydraulic accumulator, for damping pulsations in a fluid system, as for example the pressure pulses from a fuel pump.

Pulse

A change in electrical or mechanical signal.

Pulse Air Injection

An emission control system that uses exhaust pressure pulsations to draw air into the exhaust gas flow to increase the available oxygen in the catalytic converter.

Pulse Generator

Inductive electronic device that provides information to the ignition amplifier or ECU on engine position.

Pulse Shaping

The action carried out in an ECU to a signal from a sensor. For example, a sine wave may be changed to a square wave.

Pulse Wheel

Toothed sensor wheel used to induce or affect electrical currents in magnetic inductive pulse generators, such as engine speed and position sensors.

Pulse Width

The operating phase of an actuator when it is energised by an electronic control unit.

Pump

Device that is electrically or mechanically driven to pressurize a fluid or gas.

Punctuation

The use of marks and signs to form words, sentences, paragraphs etc.

Purge Valve

The valve in a fuel vapour evaporative system operated from the ECM under specific conditions to draw air back through the evaporative canister. An emission control device to prevent hydrocarbon fuel vapours from the fuel tank escaping into the atmosphere.

Push Fit

The relationship between the dimensions of two components where one fits inside the other. In this instance the fit is one where the inner dimension of the outer component is the same as the outer dimension of the inner component. Also known as a transition fit.

Push Rod

A rod that transfers movement from a cam follower to a rocker arm.

PWR

Power to Weight Ratio

Pyrotechnic

Explosive devices!

Pyrotechnic Inflater

An explosive device used to produce a large quantity of gas to inflate an air bag.
Q

QC

Quality control

Qt

Quart"

Quadralink

A four link suspension system developed by Ford.

Quadrant

A mechanical lever shaped as a quadrant usually with three or more points for transmitting movement.

Quadrant and Pinion

Mechanism to raise and lower window. Similar to rack and pinion but with the rack on the circumference of the quadrant.

Quadricycle

Four wheeled vehicle with a max ULW of 400kg (550kg for a goods vehicle) with a max net power of 15KW.

Quarter Panel (Rear quarter)

Side Panel which is generally a quarter of the total length of the vehicle and extends from the rear door to the end of the car.

Quartile

Any three points that divide an ordered distribution into four parts. Each of these parts contain a quarter of the score.

Quartz

A type of glass that will withstand very high temperatures.

Quartz Halogen Lamp

High intensity light bulb with a quartz glass bulb and filled with a halogen gas.

Quenching

A process of rapid cooling.
R

Racist

Intolerance of race. A person with prejudiced belief that one race is superior (better) than another.

Rack

Gear teeth cut on a straight bar or rod.

Rack and Pinion

Type of steering system gearing.

Radial

Outwards from the centre and at right angles to the axis.

Radial (Tire)

Tread supported by crown plies and casing plies laid radially.

Radial (Tyre)

Tread supported by crown plies and casing plies laid radially.

Radial Force

A force that acts outwards from a centre point.

Radial Groove

A groove running radially, or radiating from the centre and around a component.

Radial Play

Free play at right angles to the axis.

Radial Runout

Out of true movement at the periphery of a rotating circular component.

Radial-piston

Usually refers to a pump where a number of pistons are used that act outwards from the centre.

Radiation

The emission and diffusion of rays.

Radiator

An apparatus for radiating or diffusing heat.

Radiator Cap

Cap used to pressurise cooling system.

Radius

The straight line distance from the centre of a circle to any fixed point on the circumference.

Radius Arm

Suspension link with a fixed inner bearing and support for the stub axle assembly at the outer end.

Rail

(1) Gear selector component carrying the selector forks in a manual transmission. (2) Pressurised petrol supply tube for all fuel injectors in a port electronic fuel injection system.

RAM

Random Access Memory. Dynamic memory in computers which holds data being worked on. This data is not permanent and will be lost when power is switched off.

Ram Air Effect

Forced movement of air due to the movement of the vehicle.

Ram Cylinder

Hydraulic cylinder that applies force to a rod. Often part of a steering system.

Ram Pressure

Pressure caused by air of fluid movement.

Range

The difference between the highest and lowest numbers.

Range Change

(1) High and low gear ratios for an off-road or sport utility vehicle. (2) Secondary gearing in a large goods vehicle transmission gearbox that couples with the primary gears to double or treble the overall gear ratios.

Rare earth magnets

These magnets are made from substances which hold a more dense magnetic flux than regular magnets. This means more power for the weight. Rare earth magnets are always preferable although not necessary as they can be expensive.

Ratchet

A mechanism consisting of a toothed wheel, the ratchet, and a locking or actuating pawl. Used to either prevent the pawl lever or the wheel from rotating in one direct only or in some mechanisms to drive the wheel forward.

Ratio

The numerical relationship between two or more components transmitting a force or movement.

Ravigneaux Planetary Gears

An epicyclic gear set with two sun wheels and planetary gears on a common annulus.

Re-face

Term used to describe the action when the face of a valve or other component is machined.

React

To respond.

Reaction

An equal and opposite force.

Reaction Member

The held component of an epicyclic gear train that produces the specific gear ratio when held.

Reactor

Part of a fluid flywheel that reacts to the movement of fluid.

Ready-To-Spray

Describes paint which has been properly mixed with all necessary components and is ready to apply to the substrate. A variation is 'Ready-for-Use' (RFU) which refers to material that is purchased ready to apply straight from the container.

Reamed

Accurate cutting of a hole using a reamer.

Rebore

Recutting of a cylinder bore to an oversize dimension to remove wear and or damage. The cylinder is then fitted with oversize pistons.

Rebound

Suspension movement following compression of the spring when the energy of impact is released.

Receiver

Device used to receive or pick up radio signals or similar.

Receiver/Drier

Part of an air conditioning system in the high pressure side between the condenser and expansion valve that acts as a reservoir and as a filter and drier for the refrigerant.

Recess

An undercut area in a component usually machined to give access for a fixing or another component.

Recharging

Putting back the electricity taken from a battery.

Reciprocal

The value of something when divided into one. The reciprocal of R is 1/R.

Reciprocating

Moving backwards and forwards.

Recirculating Ball Steering

A steering gearbox using the nut and worm principle. It has a series of ball bearings forming the thread of the worm, which gives a very smooth operation.

Recoating

The application of fresh paint material over a recently painted material.

Recombinant Battery

A type of battery design which has slightly more negative plate material than positive plate material allowing the oxygen released by the positive plates, near to the fully charged position, to combine with the negative plate so that no gases are discharged.

Rectifier

An electrical device that converts alternating current AC to direct current DC.

Reduce

To lower the viscosity of a paint by the addition of solvent or thinner.

Reducer

A solvent used to reduce or thin paints to sprayable viscosity.

Reduction Gear

A gear (or more often pair of gears) used to reduce the speed of a shaft.

Redundant

In the context of systems or message transmission, redundant means extra information on say another channel that may not be used except for checking.

Reed Relay

Thin steel contacts that are joined when they become magnetic. The magnetism is created by a small coil, usually in series with a bulb.

Reed Switch

Thin steel contacts that are joined when they become magnetic.

Reference Voltage

A voltage value used in an electronic control module that is conducted to a sensor and against which the return voltage is measured in order to determine the signal value.

Refinish

Repair of an OEM or previously painted substrate.

Reflector

Body or surface reflecting rays, particles, objects. Legal requirement on rear of vehicles.

Refraction

Deflection at a certain angle when light enters obliquely from another medium of different density (light lens).

Refrigerant

The gas in an air conditioning system. It is condensed to a liquid by pressurisation and the heat in the refrigerant is taken in or passed out during the changes of state from liquid to gas and from gas to liquid. Two refrigerants are used for vehicle air conditioning. These are R12 and R134a. These must not be mixed or allowed to escape to the atmosphere.

Regenerative braking

A regenerative brake is an energy recovery mechanism that reduces vehicle speed by converting some of its kinetic energy and/or potential energy (due to elevation) into a useful form of energy instead of dissipating it as heat as in a conventional brake.

Regulator

An electronic device for controlling the output voltage from a generator.

Regulator Terminals

Terminals on the regulator that connect to, for example, a warning light, field windings, sensing supply and ignition. Some also output signals to the engine management ECU.

Reinforce

To make information sink in.

Relative Density

The ratio of the density of one substance to the density of water. Used to measure battery acid strength. Specific gravity is a similar but older term.

Relay

Electromagnetic switch used in electric circuits to reduce load on smaller switches.

Relay Coil

The winding in a relay that when power is supplied to it, causes magnetism, which in turn makes the relay contacts close.

Relays

Electromagnetic switches used in electric circuits.

Release Bearing

Shaft-mounted thrust bearing that transmits the action of the clutch pedal to disengage the clutch.

Release Fingers

The fingers in a circular section of the diaphragm on a clutch that move when the release bearing is operated.

Release Fork

The actuating lever that moves the release bearing of a clutch.

Release Levers

See Release Fork.

Release Mechanism

Components joining the clutch pedal to the pressure plate of the transmission clutch.

Release Shaft

Pivot for the clutch release lever.

Relevant Information

The suitability of information based upon your needs.

Relief Valve

See Pressure Relief Valve.

Reluctance

A measure of resistance to magnetic forces.

REMCO

Remote adjustment for CO.

Remote Starter

A switch, usually connected directly to the solenoid terminal of the starter motor, to allow remote operation during repair or testing.

Renewable resource

A natural resource is a renewable resource if it is replaced by natural processes at a rate comparable or faster than its rate of consumption by humans. Solar radiation, tides, winds and hydroelectricity are perpetual resources that are in no danger of a lack of long-term availability.

Replacement manual pages

Replacement pages are normally sent out under a Special Notice. They must be inserted into the manual immediately. Superseded pages should be removed.

Research

To study something thoroughly.

Reserve Capacity

The time for which a battery will produce 25A at 25C.

Reservoir

A container holding a supply of liquid, gas, air or vacuum in a system.

Residual Magnetism

The magnetism held in an electromagnetic pole after the electrical current has been turned off. Natural magnetism in a magnet.

Residual Pressure

The pressure held in a hydraulic line after a valve has closed and is used to reduce the pressure build up time when next applied.

Resilience

A property of material that has the ability to absorb energy from sudden loading by extension and resistance to fracture from stress loadings.

Resin

A solid or semisolid material, usually polymeric, which deposits a film and is the actual film-forming ingredient in paint. Solutions of polymers are often called resins, but the term actually applies only to the film forming solids, not to the solution.

Resistance

(1) Electrical resistance, the Ohm, is a measure of the opposition to electrical current flow in a conductor. (2) A force that acts in opposition to another.

Resistance Test

A measurement of resistance using an ohmmeter.

Resistor

Electrical device which has resistance to the passage of current.

Resistor Pack

Set of dropping resistors used as part of a heater motor circuit to set different speeds.

Resolution

The number of pixels per square inch shown on the computer screen. The greater the resolution the better the picture.

Resonant Frequency

Vibration at the natural frequency of a component.

Resonant Noise

A noise that results from vibration at the natural frequency of a component.

Resonator

Component of the exhaust system to reduce noise.

Resources

Sources of information, expertise and knowledge.

Respirator

A device worn over the face to filter particles and fumes out of the air being breathed. Modern 2K paints require the use of air-fed respirators which provide an efficiently filtered supply of air at a positive pressure around a half-or full-face mask worn by the painter.

Restrictor

A narrowing of a passage used to control flow of a gas or liquid.

Resultant Force

A force acting in one direction as result of other forces acting on an object from other directions.

Retarder

A slow-evaporating solvent added to a paint to prolong the drying time. Typically used to reduce orange peel or blushing.

Retrofit

The fitting of a system after the vehicle has left the factory or later in its life.

Retrofitted

Retrofitting refers to the act of adding new technology or features to older systems.

Return

Pipe or similar where, for example, fuel is returned to the tank.

Return Spring

Simple spring to move an item back into its rest position.

Revcounter

A tachometer that indicated revolutions per second.

Reverse Bias

An electrical term applied to semiconductors and transistors which normally allow the flow of current in one direction only but will allow current to flow in the opposite direction under specific conditions.

Reverse Switch

A switch operated by a gearbox component that illuminates the reverse light.

Reversing Circuit

A circuit using changeover switches or relays that reverses the voltage supply to a motor.

Review

To look over and study information again.

Revision

To review information in order to remind yourself of its content.

RFI

Radio frequency interference. Electromagnetic radiation from an electrical source.

RfR

Reason for Rejection

RHD

Right-Hand Drive

Rheostat

A type of variable resistor having only two terminals.

Rich Fuel/Air Mixture

A fuel/air mixture with a ratio greater than the stoichiometric ratio of 14.7:1. A mixture strength with an excess of fuel.

Rim

Outside edge, periphery. Part of wheel carrying the tyre.

Ring Gear (Starter)

A large diameter gear wheel mounted on the engine flywheel or torque converter flex plate and used to engage with the starter motor drive pinion to start the engine.

Ring Groove

Slot cut round the piston for the piston rings to sit in.

Ring Land

Seating area for piston rings.

RIRO

Rubbish In Rubbish Out. In relation to the Internet.

Road Adhesion

Grip between the tyres and the road surface.

Rocker

A component such as a lever to operate a valve due to action of a cam.

Rocker Arm

Arm that works on a rocker shaft to open a valve on an overhead valve engine.

Rocker Shaft

A shaft, usually at the top of an overhead valve engine, on which the rockers pivot.

Rocker Switch

A switch that has two or three positions. Often used with the centre as an off position and then with a voltage reversal process as it is rocked in either direction.

Roll

Vehicle body movement from side to side.

Roller Bearing

A type of bearing consisting of a series of parallel rollers held in a cage between inner and outer bearing tracks.

Roller Pump

A type of fuel pump that uses a rotor and a series of parallel rollers in an elliptical casing to produce the pumping and carrying chambers of the pump. Usually electrically driven and used on many fuel injection systems.

Roller-Cell Pump

A type of fuel pump that uses a rotor and a series of parallel rollers in an elliptical casing to produce the pumping and carrying chambers of the pump. Usually electrically driven and used on many fuel injection systems.

Rolling Resistance

The frictional value for the circumferential surface of a rolling component in contact with the track or road on which it runs. An example is the rolling resistance of a road tyre on various road surfaces.

Rolling Road

Rollers set into the ground on which the wheels of a vehicle can be run. The system can then be used to check performance under driving conditions.

ROM

Read Only Memory in a computer, which is the permanent memory that is retained even when the power is switched off.

RON

Rated Octane Number

Roof

Additional structural panel of vehicle body.

Roots Supercharger

Type of mechanical pressure charger using two twin or triple lobed rollers to form an air pump in the inlet tract of an engine.

Rotary Air Valve

A valve that uses a shutter to cover a hole depending on the amount of rotation. Usually used to refer to an auxiliary air valve on an injection system.

Rotary Control Valve

Power steering control valve coupled to the steering column, which operates by inner and outer components coming together to open valve orifices to allow hydraulic fluid flow.

Rotary Movement

Circular motion. Movement provided by the basic gear wheel or crank.

Rotary Oil Pump

A positive displacement oil pump that uses two rotors inside a housing. There is an eccentrically driven rotor with eternal lobes that mesh with the internal lobes of a driven rotor. The external rotor has one more lobe than the internal rotor and this forms the pumping and carrying chambers of the pump.

Rotary Pump

Type of diesel fuel injection pump.

Rotoflex Joint

A propeller shaft universal joint using a sleeved hexagonal rubber ring between alternate three pointed couplings on each of the two connecting shafts.

Rotor

A component that rotates! Such as a brake disc, alternator rotor or oil pump rotor.

Rotor Windings

Copper windings that create the magnetic field on the alternator rotor.

Rounding Off

Express as a round number (i.e., 4.7 rounded off becomes 5)

RPM

Revolutions per minute.

RSI

Repetitive Strain Injury. This type of injury occurs from repeated physical movements. It can be caused by bad typing technique, bad posture and lack of adequate rest and breaks. RSI is common in the wrists.

RTV

Room temperature vulcanizing. A type of form-in-place gasket material.

Rub-through

The result of sanding or buffing through one layer of paint and into the substrate below. A rub-through is common from clearcoat to basecoat or from primer to metal.

Rubber Mountings

Hard rubber connection units used to insulate one component from another to reduce vibrations and noise.

Rubbing Compound

An abrasive that smoothes and polishes the paint film. Also known as polishing compound.

Run-out

A measure of the out-of-true state on the face or faces of rotating components such as brake rotors and the clutch face on engine flywheels.

Runner

An engine intake tube joining the plenum chamber to the inlet port in the cylinder head.

Running Clearance

A small gap between moving components that allows movement and lubrication.

Running On

The term applied to an engine that continues to run after the ignition has been switched off. Also run on and dieseling.

Runout

A measure of the out-of-true state on the face or faces of rotating components such as brake rotors and the clutch face on engine flywheels.

Rust

The corrosion product that forms on a steel surface when it is exposed to oxygen and water. Also known as oxidation.

RWD

Rear Wheel Drive.

Rzeppa Joint

A type of constant velocity joint used on vehicle transmission drive shafts. It has 6 steel balls in a cage between inner and outer elliptical housings.
S

S Classification (SAE)

Engine oil suitable for gasoline engines. The second letter in the classification denotes the quality and minimum conditions that the oil must meet.

S.W.L

Safe Weight Limit."

SAE

Society of automotive engineers. SAE International is the premier membership society dedicated to advancing mobility engineering worldwide. SAE is a global technology information and standards organisation.

Sagging

Excessive flow on a vertical surface resulting in drips and other imperfections on the painted surface. Can Occur not only when the paint is wet, but also during baking in certain types of paints.

Sand

To smooth a surface with an abrasive paper or cloth.

Sandblasting (grit-blasting)

A method of cleaning metal, usually steel, by applying an abrasive with pressurised air. This is a very efficient method of removing paint and corrosion prior to repainting.

Sander

A power tool used with abrasives to roughen up or smooth surfaces quickly.

Sanding Block (Rubbing block)

A hard, flexible block to provide a smooth, consistent backing for abrasive papers used in hand sanding.

Sandscratch Swelling

Exaggerated distortion of sanding marks in the underlying surface, usually caused by solvents in the topcoat attacking the substrate.

Sandscratches

Tracking in the topcoat of sanding marks in the substrate. Usually caused by either flatting with abrasives that are too coarse, or failure to adequately fill sanding scratches with primer fillers/surfacers

Satellite

This can refer to any celestial body orbiting around a planet or star but usually means man-made equipment that orbits the Earth.

Satin

A surface finish that is approximately half-way between gloss and matt

Saturation

A term referring to a colour's purity or richness. The more chroma in a colour, the more saturated that colour is.

SAW

Spark advance word output signal.

SC

Supercharged

Scan Tool

Diagnostic tool that connects to an electronic control module on a vehicle to read fault codes and other data.

Scanner

Diagnostic tool that connects to an electronic control module on a vehicle to read fault codes and other data. Some scanners can also connect to controller area networks (CAN).

Scanning

To skim/scan text in order to get a general idea about it.

Scavenge Pump

The oil pump in the oil pan of a dry sump (oil pan) engine that returns the lubricating oil to a separate reservoir.

Scavenging

The process in the combustion chamber that clears the residual exhaust gases by the incoming air charge. The inlet and exhaust valves are both open for a very brief spell as the engine moves across top dead centre at the end of the exhaust stroke.

Schrader Valve

A spring loaded valve for retaining the pressure in a tyre and to allow for tyre inflation. Fitted into the rim of a wheel either as a separate valve for tubeless tyres or as part of the tube for tubed tyres.

Sciatica

Neuralgia of the hip and thigh.

Scope

Short for oscilloscope - Test equipment with a screen that can display electrical signals.

Scraper Ring

Piston ring that controls amount of oil on cylinder wall.

Screw Thread

A method of increasing force.

Scrub Radius

Effect on the tyre of steering turn.

Scuffing

A rubbing wear due to lack of lubrication or incorrect alignment. Examples are cylinder scoring and tyre tread wear on one side of a tyre only.

Seal

Oil, water or gas tight join.

Seal Land

The area on shafts that an oil seal lip seals against.

Sealant

A liquid material that is used with or, in place of, a gasket to give a gas or liquid seal. Sealants can be either fully setting and go hard after application or non-setting which remain flexible in use. The correct type of sealant should be selected.

Sealer

An undercoat that enhances adhesion by providing a barrier between the underlying paint and the new paint. Provides uniform colour holdout and an even, level surface for topcoat application.

Sealing Ring

A rubber (or similar material) ring that fits in or against an item to make an air or liquid tight seal.

Sealing Strip

Gasket to prevent leaks.

Search Engine

A program that enables you to locate information on the World Wide Web using keyword searches.

Seat

A machined face for making a good seal when matched with a valve.

Secondary Brake

Back up brake system, either mechanical or a split line hydraulic layout.

Secondary Cells

The cells of a rechargeable battery.

Secondary Shoe

Trailing shoe in a drum brake.

Secondary Winding

The high tension (secondary circuit) coil of wire in an ignition coil.

Seeding

The development of tiny insoluble particles in paint (in the can) which results in a rough or gritty film.

SEFI

Sequential Electronic Fuel Injection.

Seismic Mass

A small mass (weight) that moves to act as a sensing element.

Seizure

Lock up of mechanical parts preventing or restricting proper movement.

Selector Clutch

Part of gear change system that automatically synchronises gear speeds before they are engaged.

Selector Fork

A fork that acts on, and moves a gear selector.

Selector Lever

Any lever to control a system that the driver uses to select a function.

Selector Mechanism

The mechanical connection between the driver and the gearbox shift hubs in a manual transmission.

Selector Shaft

Simple shafts that are attached to and move the selector forks, which in turn move the synchronisers.

Self Test

See Self-Test.

Self-Adjusting

A mechanism or component that takes up free play automatically by either a mechanism or hydraulic pressure.

Self-diagnostics

A system where the ECU can determine if an error has occurs in its own inputs, outputs or systems.

Self-monitoring

A system where the ECU can determine if an error has occurs in its own inputs, outputs or systems.

Self-Servo Action

Description of how the leading shoe on a drum brake system is pulled by the drum such as to increase its braking effect.

Self-Test

Start up and monitoring sequences for electronic control systems. Produce fault code data and triggers warning signals.

Semi Floating Axle

An axle hub arrangement with one bearing mounted inside the axle casing where it supports the axle shaft. The load is carried by the shaft which has shear and bending forces applied to it.

Semi-conductor

A material that can be made to conduct or block electricity. A diode is a good example.

Semi-elliptical Spring

A suspension leaf spring consisting of one or more leaves with mounting eyes or slippers at the ends and having a curved shape.

Semi-gloss

An intermediate gloss level between high and low gloss.

Semi-trailing Arm

A rear suspension type with a triangular trailing arm that has the chassis mounting points set at an angle to the transverse axis of the vehicle.

Semiconductor

A material that can be made to conduct or block electricity. A diode is a good example.

Sender Unit

Another name for a sensor.

Sensor

Electronic components that send electrical signals to the ECU.

Sensors

Electronic components that send electrical signals to the ECU.

Sequence

One thing that follows on to the next in time.

Sequential Fuel Injection

A petrol fuel injection system using ported injection timed in sequence with the engine firing order.

Sequential Injection

See Sequential Fuel Injection

Serial Fault Reader

Equipment that connects, usually to the OBD plug or similar, to read stored faults in an electronic system. See also scanner.

Series Circuit

Any electric circuit having all elements joined in a sequence such that the same current flows through them all.

Series hybrid

An engine drives a generator which in turn powers a motor that drives the vehicle.

Series Resistor

A resistor in a circuit that is connected in-line with the supply.

Serpentine Belt

A single flexible drive belt that provides a drive from the engine crankshaft to all ancillary components. Replaces a series of individual belts.

Servo

A servo mechanism (informal)

Servo Cylinder

Ram cylinder that supplements physical forces in operating a control (as for example steering, a brake or clutch), either by direct mechanical amplification or by external power assistance.

Servomechanism

System or device that supplements physical forces in operating a control (as for example a brake or clutch), either by direct mechanical amplification or by external power assistance.

Servomotor

A motor that supplements physical forces in operating a control.

SES

Service Engine Soon (light)

Settling

Gravity separation of one or more components from a paint and the resulting layer of material on the bottom of a container.

SFI

Sequential Fuel Injection

Shackle

Part of a leaf spring suspension system that allows movement (swinging shackle) or is fixed to the chassis (fixed shackle).

Shackle (Slipper)

Allows for changes in length between the ends of a leaf spring as suspension moves.

Shade

Variation of a colour. A colour that is basically blue can have a red shade or yellow shade as well as being blue. Shade is also called tone or undertone, since it describes the subtle tone of a colour.

Shampoo

A cleansing agent consisting of soaps or detergents used for washing the hair – or a car!

Sheen

The gloss or flatness of a film when viewed at a low angle.

Sheer Force

A force that tends to sheer or cut something much like the action of scissors.

Sheet Moulded Compound

Fibreglass or thermoplastic plastic material moulded to shape and used as an outer panel on a vehicle.

Shell Bearings

Plain bearing formed from two interlocking and abutting thin walled semi-circular cups.

Shift Fork

A fork that acts on, and moves a gear selector.

Shift Ring

Part of a gear selector mechanism.

Shift Rod

A simple rod that connects the gear change lever to the gearbox.

Shift Shaft

A shaft that is used as part of a gearshift / gear changing mechanism.

Shift Timing

The point at which an automatic gearbox changes gear.

Shim

A thin metal sheet or washer used between two components to adjust free play. Shim material is produced in standard sizes.

Shimmy

Side to side movement of the wheels that causes the tyres to lose some grip on the road.

Shock Absorber

Method of dampening suspension spring shock oscillation. Damper.

Short Circuit

A short circuit is one that allows a current to travel along a different path from the one originally intended.

Short Engine

Engine block containing crankshaft and pistons. Usually referred to when being replaced to overhaul the engine.

Short Motor

The engine block and crankcase together with all internal running components, pistons, crankshaft, etc.

Shrink Fit

An interference fit obtained by heating the outer component or cooling the inner component so that they can be assembled with a push fit. When the temperatures are balanced the parts retain their interference fit.

Shrinkage

Loss of solvent during the drying/curing process of a paint film.

Shroud

General term used to describe a cover.

Shunt (Electrical)

A parallel part of an electrical circuit. An example is the shunt windings of some starter motors.

Side Draft

A carburettor where the choke tube (venturi) is fitted horizontally.

Side Thrust

Forces caused by cornering.

Side-draught Booth

A spray booth in which air movement is from the front to back.

Side-tone

Viewing the repaired area from an angle just past the reflection of the light source.

Siemens

Siemens IT solutions and Services Ltd – Service provider for MOT Computerisation.

Significant Figures

The number of digits expressed in a measurement. Sig. fig. can appear before and/ or after the decimal point.

Signposting Guidance

within the specifications for the new AS levels A levels and GNVQs, opportunities for developing or producing evidence for assessment of key skills.

Silencer (Muffler)

A component in the exhaust system to absorb the gas shock waves and noise in order to reduce the emitted noise from a vehicle engine. Also known as a muffler.(US term).

Silicon

One of many polymeric organic compounds of silicone with high resistance to cold, heat, water and passage of electricity.

Silicone

A chemical compound with excellent water repellency and a slippery feel. Silicones are commonly used in automotive waxes to enhance application and ease of removal, and to increase gloss and durability. The term 'Silicones' is often applied to the defect known as 'cratering' or 'fish-eyes'

Simple Gear Train

Two or more gears in direct mesh.

Simulation

Simulation is the imitation of some real thing, state of affairs, or process. The act of simulating something generally involves representing certain key characteristics or behaviours of a selected physical or abstract system.

Simulations

Activities that simulate or model reality.

Simultaneously

Two or more things happening at the same time.

Sine Wave

The wave pattern of an AC current. The positive and negative patterns are an inverse copy of each other.

Single Point Injection

A petrol fuel injection system using a single point injector in a throttle body in the inlet air supply and positioned on top of the inlet manifold. Also throttle body injection (TBI)."

Sinkage

A condition in which the topcoat appears to sink into the primer coat causing a loss of gloss. Also, a loss of gloss due to improper solvent selection.

Sintering

A manufacturing process using heat and pressure to form metal and composite components. Examples are brake lining materials and some components traditionally produced by forging or hot stamping.

Sipe

Very narrow groove or cut in the tyre tread that aids the dispersal of surface water between the tyre and road.

SIPS

Side Impact Protection System

Skidpan

Special test track for skidding on!

Skim-reading

To skim/scan text in order to get a general idea about it.

Skinning

The formation of a thin, tough film on the surface of a liquid paint film, usually due to oxidation, hardening, or drying of the paint.

SLA Suspension

Short and long transverse suspension arms. The upper arm is the shorter of the two. The geometry of this layout keeps the wheel camber reasonably constant during suspension movements. Also known as 'unequal wishbones'.

Slave Cylinder

A hydraulic cylinder receiving a force and operating a mechanism. Examples are the clutch cylinder and the brake or wheel cylinders in brake units.

Sleeve (Cylinder)

A steel sleeve used to form a running surface for pistons in an engine. Also known as a cylinder liner.

Sliding Caliper

A brake caliper that has one piston and one sliding section.

Sliding Joint

A drive shaft joint with the ability to change length and to transmit movement usually with a splined construction.

Sliding Resistance

The frictional value for the surface of a sliding component in contact with the track or road on which it runs. An example is the sliding resistance of a road tyre skidding on a road surface. The sliding resistance is usually less than the rolling resistance.

Slinger

(1) A plate fitted on a rotating shaft in front of an oil seal to reduce the volume and pressure of the oil on the seal. (2) A plate or protuberance on a crankshaft for throwing oil onto the cylinder walls or other components.

Slip

Loss of grip between two frictional faces.

Slip Angle

The difference between the true line and the actual line of a vehicle wheel when cornering.

Slip Ring

Continuous ring of copper used with a brush to transmit electricity through a rotating component.

Sludge (Oil)

Lubrication oil deterioration where the oil thickens, mixes with contaminants and forms a thick and glutinous jelly or paste.

Sludging

Description of what happens to oil if it is not changed as recommended - a sludge forms that looks like Mississippi mud!

Smart Card

A card issue to an authorised user to access the MOT database via the VTS Device.

Smoke Meter

Opacity meter used to measure the amount of smoke in diesel engine exhaust gases.

SN

Special Notice – an official notice issued from time to time by VOSA to inform AEs, NTs and other system users of changes to the testing scheme. SNs may also be used to highlight areas of concern and to advise of developments of the scheme.

Snail Cam

A cam that is shaped like a snail shell. In other words it has more effect the further it is turned.

Snatching

Term used to describe the action of a clutch when the take up is too sharp/severe.

SOC

State of charge (of a battery)

Sodium Hydroxide

A chemical used as the inflater for some air bags.

Soft Interface Pad

A support pad to which a finishing film abrasive disc can be attached. A soft interface pad reduces the pressure transmitted to the surface to be finished and moderates the cutting effect of the abrasive. Also used to great advantage on highly contoured surfaces.

Soft Jawed Vice

A vice with soft material fitted to the jaws to prevent damage to any components held in it.

Software

A computer program.

SOHC

Single Overhead Camshaft Engine.

Solder

A mixture of lead and tin used to join wires and terminals.

Soldered Joint

Termination of cables with solder.

Solenoid

A coil of wire. Usually used to refer to a device containing an electromagnet.

Solenoid Switch

Electro-magnetically activated electrical switch.

Solenoid Valve

A valve operated by a solenoid. Fuel injectors are good examples.

Solids

The part of the paint that does not evaporate but stays on the surface to form a film. Usually measured on a weight or volume basis.

Solution

Homogeneous liquid or mixture of two or more chemical substances.

Solvency

The ability of a liquid to dissolve a solid. Measured by the viscosity of a solution at a certain concentration of solid resin. The same solvent may have different solvency for different resins.

Solvent

A liquid which will dissolve another material, usually resins or other binder components. Commonly organic liquids.

Solvent Density

The weight per unit volume of a solvent or solvent mixture.

Solvent-Blend

The particular mixture of liquids (usually true solvents and diluents) that give a paint the desired flow or evaporation properties.

Solvent-borne

Describes a paint which contains organic solvents rather than water as its primary liquid component.

Solvent-Popping

Bumps or small craters that form on the paint film, which are caused by trapped solvent trying to escape through the drying paint.

South Pole

The term used to describe one of the poles of a magnet where the magnetic field lines of force end.

Spacer

A metal sheet or washer used between two components to adjust free play.

Spade Terminal

A flat blade terminal used to make an electrical connection.

Spark Ignition (SI)

The ignition of petrol by a spark in the combustion chamber of an engine.

Spark Plugs

Used to provide a small gap in the combustion chamber of an engine, for a spark to jump across.

Speakers

Device that converts audio signals to sounds that humans can hear.

Specific Gravity

The ratio of the density of a substance to that of water.

Spell Checker

Most computer applications (i.e., Microsoft Word, Excel etc.) will enable you to check documents for incorrect spelling.

Spelling

To form a word with a series of letters.

SPI

Single point injection. Electronic throttle body fuel injection system.

Spider

1. Arachnid with eight legs...2. Name sometimes used for the shaft on which planet gears rotate in a differential.

Spider Diagrams

A series of lines and boxes containing relevant information. A form of note taking.

Spigot

A bearing between two shafts mounted end to end axially.

Spigot Bearing

Bearing for a spigot shaft. Usually used to refer to the bearing inside the end of the crankshaft, into which the gearbox input shaft fits.

Spindle

A rotating shaft.

Spindle Arm

(1) Lever that imparts the steering action to the steering knuckle or stub axle assembly, as from a tie rod or track rod. Also steering arm, though this term is often used for the lever that imparts steering action from drag link to steering knuckle. (2) An intermediate arm in a steering system.

Spindle Bushes

Simple bearings on which a spindle rotates.

Spiral spring

These are generally made of rectangular section material, flat strip, with round edges. They are general used as brush springs in D.C. motors. Also known as clock springs

Spirit Level

A device full of liquid with a bubble that moves to the centre when it is level.

Splice

A joint in two or more cables made by crimping or soldering the cables together.

Spline

Axial groove on a shaft and hub.

Splined Joint

A toothed joint between two shafts that will transmit rotation but also allow axial (back and forth) movement.

Splines

Axial grooves on a shaft and hub.

Split Pin

A soft steel pin that has two sides that are folded out to secure the pin in a hole. Sometimes called a cotter pin.

Split Rings

Two continuous rings of copper used with brushes to transmit electricity through to a rotating component such as an alternator rotor field winding.

Split Slip Ring

Two continuous rings of copper used with brushes to transmit electricity through to a rotating component such as an alternator rotor field winding.

Splitter

Tool used to split ball joints or track rod ends from the steering arms.

Spokes

Thin metal rods that join the wheel hub to the rim and support the weight of a vehicle.

Spongy (Brakes)

Usually caused by air in the hydraulic brake lines. A soft and imprecise feel to the brake pedal.

Spot Repair

A type of refinish job in which a section of the vehicle smaller than a panel is refinished. The paint is usually blended into the surrounding area.

SPOUT

Spark output Signal.

Sprag Clutch

A uni-directional rotary clutch that uses a series of shaped (like a figure 8) rollers and springs to either freewheel or grip the outer tracks to transmit a rotating force.

Spray Booth

An enclosure used to paint vehicles. Spray booths have controlled air flow and normally have temperature control or baking capacity.

Spray Gun

A device that mixes paint and compressed air to atomise and control the spray pattern as the paint leaves the fluid needle and air cap.

Spraying

Paint is atomised in a spray gun and the stream of atomised paint is directed at the part to be painted. Atomisation is normally achieved using high pressure air, by high fluid pressure, or by electrical means as in an electrostatic process.

Spreader Valve

The adjustment valve on a compressed air spray gun which directs an air stream against the sides of an atomised paint cloud to adjust the spray pattern.

Spreadsheet

A computer program often used to create financial forecasting documents.

Spring Clip

Small fixing device that can usually be removed by hand.

Spring Eye

A hole formed at the ends of leaf springs to allow fixing to the chassis.

Spring Ring

Small spring fixing device like a circlip.

Sprockets

Gear wheels usually used to drive or be driven by a chain.

Sprung Mass (Weight)

The part of the vehicle supported by the suspension springs.

Spur Gear

A gear wheel with straight cut teeth.

Spurious Data

Data that falls outside what is expected.

Square Metre

The area enclosed by a square with sides of 1 metre long.

Square Wave

The wave pattern formed by a digital signal.

Squeal

High pitched noise (screech) from friction components. Examples are brakes, clutch and drive belts.

Squeegee

A flexible rubber blade used to wipe off excess water from washed or wet sanded areas.

Squirm

A twisting or side-to-side movement.

SRI

Service Reminder Indicator.

SRS

Supplementary Restraint System.

SRT

System Readiness Test

SS

Speed Sensor

SSI

Solid State Ignition

Stabiliser Bar

A torsion bar that connects the suspension on each side of a vehicle's axle to transmit movement from one side to the other in order to reduce vehicle roll when cornering.

Stabilizer

An additive included in a paint mixture to prevent degradation during storage.

Stall Speed

The maximum engine speed (rpm) of a vehicle with automatic transmission that can be obtained at full throttle against the brakes without moving the vehicle. A test procedure to check the torque converter.

Stalling

When an engine stops because it is running too slowly or due to some other influence such as a learner driver!

Stamping

A manufacturing process using punches and dies to cut objects out of sheet materials.

Standard Form

Used so that very large or very small numbers can be written in a more convenient way.

Standards moderation

The means by which awarding bodies ensure consistency across centres and ensure that national standards are being maintained and applied.

Star Wound Stator

An alternator stator winding with the three-phase coils connected at the centre in order to give a large voltage output. The normal winding for light vehicle applications. Also 'Y' type stator.

Starter Motor

A powerful electric motor that produces high torque to rotate the engine for starting.

Starter Solenoid Feed

Small wire that causes the solenoid to operate. Feed is from the starter switch and usually a relay.

Starter Switch

The switch that operates the starter motor. Usually part of the ignition switch.

Static

A term that indicates components that are stationary. The opposite of dynamic when the components are in motion.

Static Balance

The balance of a rotating component about the rotational axis. Wheel balance has both static and dynamic quantities.

Statistics

Numerical data.

Stator

Stationary part of machine. Examples are the magnetic inductance component of an alternator and the reaction member in a torque converter.

Stator Windings

Electrical windings on the stator of an alternator.

STC

Self-Test Connector.

Steel

A ferrous metal commonly used as a substrate for paint, which must be painted to prevent corrosion.

Steering

Mechanism or means whereby the direction of a vehicle is controlled.

Steering Arm

(1) Lever that imparts the steering action to the steering knuckle or stub axle assembly, as from a tie rod or track rod. Also spindle arm (US), though this term is often used for the lever that imparts steering action from drag link to steering knuckle. (2) An intermediate arm in a steering system.

Steering Axis

The point about which the steered wheel turns.

Steering Column

The linkage and outer housing between the steering wheel and the steering gearbox/rack.

Steering Gear

Small pinion that operates the steering rack. OR Worm gear that operates a steering arm.

Steering Gearbox

Gearcase in which the rotary movement of the steering column is converted into angular motion of the drop arm or pitman arm.

Steering Geometry

(1) Position of the wheel and steering swivel mountings. (2) Combination of angles in steering swivel.

Steering Nut

Part of a steering gearbox that moves on the worm gear.

Steering Rack

System where a small pinion works on a flat gear (rack) to move the steering arms.

Steering Shaft

The shaft that rotates as the steering wheel rotates.

Steering Swivel

The turning component that carries the steered wheel, king pin, stub axle assembly and McPherson strut.

Stellite

Hard and temperature resistant metal alloy used to coat exhaust valves.

Stepper Motor

An electrically controlled motor that gives precise incremental movements.

Stepper Motors

An electrically controlled motor that gives precise incremental movements.

STFT

Short Term Fuel Trim

STI

Self-Test Input.

STO

Self-Test Output.

Stoichiometric Ratio

The chemically correct ratio for air and petrol to achieve complete combustion. An air/fuel ratio of 14.7:1.

Straight Line Sander

Sander that uses a back-and-forth movement to sand a surface using sandpaper on its shoe.

Strain

Strain is the amount of extension in size divided by the original length.

Strainer

A mesh filter for basic cleaning of oil or fuel. Usually fitted in the oil pan or fuel tank.

Strangler

Alternative term for a choke flap in a cold start device for a carburettor.

Strap Wrench

A tool used to undo filters. A simple strap tightens around the filter to grip it securely.

Strap Wrenches

See Strap Wrench.

Stratified

To form, arrange, or deposit in layers. This usually refers to the fuel air charge in a cylinder where the layer next to the spark plug is richer than the layers further away. used for lean burn applications.

Strength (of a pigment)

The opacity and/or tinting power of the pigment. The measure of the ability of a pigment to hide or provide colour to a substrate.

Stress

Stress is a measure of a force or load divided by the cross-sectional area of a material to which the force is applied (N/m2).

Striker Pin

Part of the door latch mechanism.

Strippable Coating

Also called booth coating. A sprayed peelable film which is applied to the internal walls of spray booths to provide protection from overspray. When the coating becomes sufficiently contaminated, it is easily peeled or scraped away and replaced by a new layer of strippable material.

Stroboscopic

A flashing light. A strobe light is used to check and adjust ignition timing.

Stroke (Cylinder)

The length of travel of the piston in the cylinder. Twice the throw of the crankshaft.

Strut

Term used to describe a suspension unit that operates telescopically.

Stub Axle

Alternative name for a king pin assembly or steering swivel.

Stub Axle Assembly

Alternative name for a king pin assembly or steering swivel.

Stud

Threaded rod.

Styrene

A low cost, colourless monomer which polymerizes readily. Widely used in the manufacture of fibreglass mouldings, plastic articles and polyester finishes.

Sub-Frame

An extra chassis component used to support a major part such as the engine or transmission.

Substrate

The object or material to be painted. It may be bare metal, an old paint finish, or a foundation coating applied as part of a refinishing procedure.

Suction-feed Gun

A spray gun that has the paint container connected directly below it. Air flowing across the air cap creates a vacuum and, thus, draws the paint up from the container via a metal tube.

Sump

Lower part of an engine or gearbox usually containing lubrication oil.

Sun Wheel

Central gear wheel of an epicyclic gear train or differential.

Sunroof

A fixed or operable (venting or sliding) opening in an automobile roof which allows light and/or fresh air to enter the passenger compartment. Sunroofs may be manually operated or motor driven, and are available in many shapes, sizes and styles.

Supercharger

A mechanical air pump driven from the crankshaft and used to boost the intake air charge for an engine.

Supervise

To direct, manage, or oversee; to be in charge.

Supplied-Air Respirator

A respirator that provides safe breathing air to a painter while working with paints. The air supply provides not only breathing air but positive pressure on the edges of the mask to eliminate any contaminants from the outside air.

Suppressor

An electrical device fitted in parallel with a circuit to reduce the emission of electromagnetic waves at radio frequencies.

Surface plate

A flat metal plate for gauging the accuracy of a plane surface in precision metalworking

Surfacer

A heavily-pigmented foundation coating designed to be applied to a substrate for the purpose of smoothing or uniforming the surface for the subsequent coats of paint. Usually sanding is required, although non-sand variations are available.

Suspension

Means whereby vehicle body is supported on its undercarriage, comprising springs, dampers and locating linkages.

Suspension Arms

Linkages used to construct a suspension system.

SVC

Service connector for octane and idle speed adjustment.

Swarf

Small pieces of metal that are produced during machining.

Swash-plate Compressor

See swash-plate pump.

Swash-plate Pump

A type of pump that uses a rotating plate, that is radially off-set from the axis of the shaft, to operate the pump pistons in their cylinders. This design can also be used for compressors.

SWB

Short Wheel-Base

Swept Volume

The volume inside a cylinder above the piston crown at bottom dead centre minus the volume above the piston at top dead centre which forms the combustion chamber and is given the term 'clearance volume'.

Swinging caliper

A type of floating caliper with wedge-shaped disc pads (only one of which is activated by hydraulic pressure from the piston, the other being fixed), which can pivot on its hinge pin to equalize the pressure on both pads

Swirl Marks

A pattern of small scratches left in a finished surface by the wheel of a buffer or sander during the sanding and/or compounding operation, or by hand flatting using a circular motion.

Switch Pack

General term to describe a collection of switches in one unit, window lift switches in the driver's door for example.

Swivel Axis

Line about which the steering turns.

Swivel Joints

Joints used as part of a steering linkage about which the steering turns.

Swivel Pins

Pins used as part of a steering linkage. Often called Kingpins.

Symmetrical

A description of objects that are the same on each side of their centre line.

Symptom

The observed or measures result of a fault in a system.

Synchromesh Gear

Gear change system in which the speed of rotation of a selected gear is automatically synchronized with that of the mainshaft.

Synchromesh Hub

Cone clutches that are part of a gear change system which equalises the speed of a rotating gear.

Synchronise

Two or more occurrences happening or being made to happen at the same time.

Synchroniser

Part of gear change system that automatically synchronises gear speeds before they are engaged.

Synchronization

An adjustment that causes something to occur or recur in unison.

Synchronizer

Part of gear change system that automatically synchronizes gear speeds before they are engaged.

Synthetic

Prepared or made artificially, in contrast to naturally. For example, synthetic engine oil is NOT made from crude oil!
T

T-Piece

Simple connection device to allow a pressure gauge, for example, to be connected into a pipe or fuel line.

TACH

Tachometer

Tachometer

A meter for measuring the speed of rotation of a component or device. Used to describe the on and off vehicle instruments that measure engine speed.

Tack

The stickiness of a paint film or an adhesive. The time it takes for an air-drying paint to reach a tack-free state.

Tack Cloth or Rag

A cloth coated with a non-contaminating sticky substance used to remove dirt and lint prior to painting.

Tack Coat (grip coat)

The first sprayed coat of colour, applied lightly and allowed to flash-off only until it is quite sticky.

Tack-free Time

An indicator of a coating's hardness development. The surface of the film will not finger mark, yet the film is still not dry and hard throughout.

Tandem Master Cylinder

A brake master cylinder with two separate pumping chambers. Used for split circuit brake hydraulic systems.

Tang

A projection or lug used to hold or drive an attached part. Tang on a file to hold the handle.

Tank Sender

A unit in the fuel tank that indicates the fuel level.

Tap

A tool to cut internal threads. Cutting internal threads.

Tape Tracking

Markings left behind on a new paint film when masking tape was applied before it was hard enough to resist pressure marks.

Taper

Reducing in size along the axis of an object.

Taper Roller Bearing

A type of bearing consisting of a series of tapered or conical rollers held in a cage between inner and outer bearing tracks and able to carry thrust (axial) loads as well as radial loads.

Tappet

A valve lifter or cam follower in the engine valve gear train.

Tapping Size

Thread core diameter, a drilling size.

TB

Throttle Body

TBI

Throttle Body Injection.

TC

Turbocharged

TCC

Torque Converter Clutch

TCM

Transmission or Transaxle Control Module

TCS

Traction control solenoid (SAAB 9000)

TD

Turbo Diesel

TDC

Top dead centre. The position of the crankshaft when the piston is at its highest position in the cylinder. The crankshaft is at 0° of rotation.

TDI

Turbo Direct Injection (A turbo charged direct injected diesel engine)

TDMA

Time Division Multiple Access refers to a digital communication link where multiple devices share a single carrier frequency by taking turns. Each gets the channel exclusively for a certain time slice, and then gives it up while all the other phones take their turn.

Telescopic

Acting like a telescope in having a sleeved construction where one or more sleeves slide inside the outer sleeve. Modern shock absorbers and safety steering columns are generally of this type of construction.

Temperature

A measure of the hotness or coldness of matter. The S.I. unit of temperature is the Kelvin (K) and is the same as minus two hundred and seventy-three degrees Celsius.

Temperature Differential

Difference in temperature between two components.

Tempering

Baking of plastic parts to drive off internal mould release agents prior to painting.

Tension

Force due to a pulling effort.

Tension Rod

A trailing strut or rod positioned between the vehicle chassis and a suspension track control arm to hold it in position and to transmit driving and braking forces.

Tension/Tensile

Opposing pulling forces (tension) that create a stress (tensile) in an object.

Tensioner

A device usually consisting of a small pulley to set belt tension.

Terminals

Electrical connection points. Common types are described as spade, blade, ring and fork.

Test Cycle

Strictly controlled test procedure for exhaust emission evaluations.

Test Lamp

A simple bulb used for tracing circuit faults.

Test Port

A point where a test gauge may be connected.

Test Probe

A general term used to describe the device used to make contact when testing a circuit. The prods on the end of multimeter leads are good examples.

Test Rigs

Machines designed to allow components to be run and operated as if fitted to the vehicle. Used for test and calibration purposes.

Tetraethyl Lead

A petrol additive to reduce 'knock' or detonation. Also described as an octane enhancer.

TFI

Thick film ignition module.

Theoretical Coverage

Describes a paint's film thickness or hiding power. Defined as the number of square metres a coating should cover at a specified film thickness measured in microns.

Thermal Cycling

Laboratory testing of paint formulations by alternately heating and cooling a painted object to determine what effect this variation has on the paint's properties.

Thermal Efficiency

The ratio between the heat energy in the fuel and the power output from the engine.

Thermal Expansion

Increase in size of an object as temperature increases.

Thermal Gauge

Instrument gauges that use the heating effect of electricity to move a needle.

Thermistor

Resistor whose resistance is greatly reduced by heating.

Thermo Time Switch

A device containing a bimetal strip. It is used in conjunction with a cold start injector to deliver a set amount of extra fuel when starting from cold.

Thermo-time-switch

A device containing a bimetal strip. It is used in conjunction with a cold start injector to deliver a set amount of extra fuel when starting from cold.

Thermoplastic

A type of polymer paint or plastic which softens and melts when heated and then re-solidifies upon cooling. An example is 1K acrylic lacquer paint.

Thermostat

Temperature sensing valve controlling flow of coolant.

Thermostatic Control

A device that uses temperature for actuation.

Thermosyphon

Thermosyphon (or thermosiphon) refers to a method of passive heat exchange based on natural convection which circulates liquid without the necessity of a mechanical pump.

Thick Film Ignition Module

An integrated circuit ignition control module."

Thinners

Solvent added to a paint to reduce its viscosity to a sprayable consistency.

Third Party

Another party, not one's self (legal).

Thread Pitch

Distance from the top or peak of one thread to the top of the next.

Threaded Unions

Usually pipe connections using threaded connections.

Three Phase Electric Current

The internal alternating current output from an alternator stator and made up from three single phases starting at 120 degree intervals. The three phases are rectified to a direct current output for charging the battery and supplying the vehicle electrical systems.

Three Point Seat Belt

Type of seat belt that has a single belt threaded across the lap and shoulder and anchored at three points. The anchorage points are both sides of the lap and on the pillar above the shoulder of the wearer. Also known as a lap and diagonal belt.

Three Point Static

Type of seat belt with lap and diagonal webbing.

Three Quarter Floating Axle

An axle hub arrangement with one bearing mounted in a hub on the axle casing. Although the load is carried mainly by the hub there are shear and bending forces applied to the axle shaft.

Three Way Converter

A dual bed catalytic converter with one stage coated with platinum and palladium and the other with platinum and rhodium. Converts HC (Hydrocarbons) and CO (Carbon Monoxide) to H (Hydrogen) and CO2 (Carbon Dioxide); and NOX (Nitrogen Oxides) to N (Nitrogen) and O (Oxygen).

Three-lobe Cam

A triangular shape cam.

Throttle

The engine speed control mechanism operated by the driver.

Throttle Body

A simple unit containing a throttle butterfly. Use as part of an injection system.

Throttle Body Injection

A petrol fuel injection system using a single point injector in a throttle body in the inlet air supply and positioned on top of the inlet manifold. Also single point injection (SPI).

Throttle Butterfly

The restrictor (plate) in the air intake of petrol injection ducts or carburettors.

Throttle Plate

The restrictor (butterfly) in the air intake of petrol injection ducts or carburettors.

Throttle Position Sensor

Sensor for throttle position information to engine management system.

Throttle Potentiometer

A variable resistor that is moved with the throttle to allow position of the throttle to be sensed.

Throttle Pressure

Shift control pressure in an automatic transmission regulated by engine speed and load conditions.

Throttle Spindle

The shaft on which the throttle butterfly moves.

Throttle Switch

A switch that operates when the throttle is fully open or fully closed.

Throttle Valve

A valve in an automatic transmission that responds to throttle position or inlet manifold vacuum to regulate the throttle pressure.

Throttle/Accelerator

The engine speed control mechanism operated by the driver.

Throttling Bore

A fixed size orifice used to control or restrict flow.

Through- Cure

The completion of the curing process at which no further chemical reaction can occur to aid in film formation.

Throw

The dimension from the centre axis of the crankshaft to the centre axis of the big end bearings.

Thrust

Force acting on an object causing it to change position or alignment with another object. Also used to describe a force along an axis where two components are forced together.

Thrust Bearing

Bearing intended principally to react to axial or thrust loads. Thrust race (Informal).

Thrust Face (Piston)

The side of a piston pressed against the cylinder wall during the combustion stroke. The opposite side to the connecting rod direction of travel.

Thrust Plate

A plate that applies thrust (force).

Thrust Plates

Plates used to apply thrust (pushing force) to another component.

Thyristor

A silicon controlled rectifier used as a switching device using a very low control current to switch much larger currents. Thyristors are switched on by a gate control current and remain on until the main current flow ceases.

Tick Over

Rotational speed of an engine on no-load and minimum throttle setting. Also idle or curb idle.

Tie Rod

A connecting rod in a steering system between the drop arm (Pitman arm), the idler arm and the steering arms on the steering swivels.

Time Lag

A delay in operation.

Timeliness

Reference to the time that information was recorded.

Timing

Relative crankshaft rotational points of action within the engine operating cycle particularly for ignition and valve opening.

Timing Belt

A toothed drive belt that droves from the crankshaft pulley to the camshaft. In some cases the drive is also to an ignition distributor or diesel injection pump.

Timing Chain

Chain that drives the camshaft from the crankshaft.

Timing Marks

Marks on the crankshaft pulley, flywheel, distributor drive pulley and/or camshaft pulley. Used to accurately time and an engine.

Tint

An individual pigment from a family of pigments used on a mixing machine to produce a colour match to the vehicle to be painted. Also refers to the act of colour adjustment where small amounts of tinters are added to mixed colour to correct a mismatch

Tinting Strength

The ability of a pigment to change the colour of a paint to which it is added. Some pigments have high tinting strength and only a small amount is necessary to make a large change in colour.

Tires

Tires (or 'tyres' in British English) are ring-shaped parts, either pneumatic or solid, that fit around wheels to protect them and enhance their function.

Titanium Dioxide

A non-toxic, non-reactive, white pigment. Has the greatest hiding power of all white pigments.

TIV

Thermactor Idle Vacuum Valve

TKS

Throttle Kicker Solenoid

Toe (Wheel Alignment)

The relative angle of the road wheels to the true longitudinal axis of the vehicle. The toe angle is the degree of variation needed to bring the wheels into true rolling motion when the vehicle is travelling.

Toe In

Basic setting of the road wheels on one axle when adjusted so that the front edges are angled very slightly inwards. Free play in the steering gear or suspension arms is taken up during forward motion to bring the wheels to a parallel position.

Toe Out

Basic setting of the road wheels on one axle when adjusted so that the front edges are angled very slightly outwards. Free play in the steering gear or suspension arms is taken up during forward motion to bring the wheels to a parallel position.

Toe Out On Turns

The difference between the angles of turn of the steered wheels when cornering. The angles are measured at 20 degrees for the inner wheel when checks and comparisons are being made. The outer wheel angle should be less than the inner wheel.

Tolerance

The amount that any dimension can be from the nominal size.

Toluene

A widely used solvent or diluent or a co-solvent. (Co-solvents are used to help make sure the paint forms a tough, durable film). A fast-evaporating, high solvency, aromatic hydrocarbon.

Tone Disc

A metal disc that sets the tone (frequency and volume) at which a horn operates.

Top Coat

The final layer of paint applied to a substrate. Several coats of topcoat may be applied in some cases.

Top Dead Centre

The position of the crankshaft when the piston is at its highest position in the cylinder. The crankshaft is at 0° of rotation.

Topcoat

Paint for appearance and weather seal.

Topping Off

Topping up.

Topping Up

Process of making sure a fluid is full to the top or appropriate level marking.

Torque

Rotary or turning force. The SI unit of torque is Nm. The force in Newtons multiplied by the distance in metres.

Torque Converter

A fluid flywheel with a stator that creates a back force in the turbine that is added to the force from the impellor to give an increase in output torque.

Torque Settings

Values recommended by a manufacturer, to which certain fixings should be tightened.

Torque Wrench

A calibrated wrench that allows tightening and adjustment of fasteners to a specified torque setting.

Torque-to-yield

Type of bolt used for holding cylinder heads. They are made from a steel alloy that allows a tough hold down force at the yield point of the material. These bolts usually require tightening by an angular value and replacement whenever they are removed.

Torsion

A twisting force that results in torsional stress.

Torsion Bar

Metal spring used in vehicle suspension. Uses a twisting action along the length of the spring to provide suspension movement.

Torsion Springs

A spring that works by twisting.

Torsional Strength

Ability to withstand rotational force.

Torsional Stress

The stress that occurs when twisting forces are applied.

Torx

Trade name for a hexagonal/star shaped tool that has extra machined slots for a better grip.

Total Displacement

Applied to the sum total of the swept volumes for all cylinders in an engine. Also known as 'engine capacity'.

Touch-up

Correcting minor scratches, stone chips, etc., usually by the use of a small brush.

Toughened Glass

Soft glass with tough outer skin produced by heat treatment tempering.

Towing Socket

A multisocket used to make electrical connections to a trailer.

TP

Throttle Plate.

TPI

Tuned Port Injection

TPP

Throttle Position Potentiometer

TPS

Throttle Position Sensor.

TPT

Throttle Position Transducer

Track (Wheel)

The dimension between the centres of the road wheels on one axle. Also known as tread.

Track Arm (Track Control Arm)

A transverse lower suspension arm attached to the chassis at the inner end and to a McPherson strut at the outer end. Maintains the wheel track position and transmits transverse forces.

Track Rod

Transverse rod that connects the steering arms of steered wheels and so maintains the geometric relationship between them when steering.

Track Rod End

A ball joint coupling on steering track rod ends that join the track rod to another component to allow a range of angular movement.

Tracking

In electrical terms it is the loss of an electrical current outside of an insulator. The term is also used to describe the setting procedure for adjusting front wheel steering alignment.

Traction

The grip of the tyre with the road surface. The 'grip' can be specified as a coefficient of friction where the higher the number the greater the ability to transfer a force. (1 represents 100% for all force loads, tyres are generally in the range 0.75 to 0.85).

Tractive Effort

The forward force of a vehicle while it maintains tyre contact with the road surface.

Trailing Arm

A suspension link or rod that carries an axle behind the mounting and pivoting point of the arm. Semi trailing arms are mounted at angle to the longitudinal and transverse axes of the vehicle.

Trailing Edge

The back edge of a brake shoe in relation to the direction of rotation of the brake drum.

Trailing Shoe

A brake shoe that has a trailing edge making first contact when applied.

Transaxle

(1) Rear axle assembly that incorporates the main change-speed gearbox. (2) Combined gearbox and final drive unit attached to the engine in some front wheel vehicles. Contraction of transmission-axle.

Transaxle Gearbox

(1) Rear axle assembly that incorporates the main change-speed gearbox. (2) Combined gearbox and final drive unit attached to the engine in some front wheel vehicles. Contraction of transmission-axle.

Transducer

An electronic device that converts a minute amount of one form of energy to another. A moving wheel with a tooth pattern can induce a voltage in a coil of wire around a magnet. This arrangement is used for speed and position sensors. Other transducers are used for other sensor applications.

Transfer Box

The gearbox that splits drive front and rear for four wheel drive transmissions.

Transfer Box/Case

The take-off gearbox for four wheel drive transmissions.

Transfer Efficiency

The measure of paint material applied compared to the amount of material originally sprayed. Modern HVLP spray guns are expected to achieve a transfer efficiency of at least 65%

Transfer Port

The port that connects the crankcase to the cylinder on a two stroke engine and is used to pass a new air/fuel charge to the cylinder when the piston descends to bdc.

Transformer

Two coils or windings that interact to step voltage up or down.

Transistors

Semi-conductor devices with three electrodes. Electronic switches and amplifiers.

Transition Fit

The relationship between the dimensions of two components where one fits inside the other. In this instance the fit is one where the inner dimension of the outer component is the same as the outer dimension of the inner component. Also known as a push fit.

Translucent/Translucency

Allowing light, but not detail to pass through. Semi-opaque

Transmission

(1) (US: gearbox) Mechanical unit containing a manual or automatic change speed gear system and associated actuating machinery. (2) (UK) Collective term for the components, such as clutch, gearbox, drive shaft, whereby power is transmitted from engine to driven wheels (mainly UK usage).

Transmission Fluid

The oil used in a transmission system - several types are used so always check data.

Transmission Ratio

Usually used to describe the overall ratio of the transmission - from the engine to the wheels.

Transmitter

Device that outputs a signal, usually a radio signal (TV or radio transmitter) but in some cases wires are used (temperature transmitter for example).

Transparent/transparency

Clear/clarity; Allowing light and detail to pass through; Not opaque.

Transverse

Any axis running across a vehicle or other object at right angles to the longitudinal axis.

Transverse Axis

Any axis running across a vehicle and parallel with the ground and at right angles to the longitudinal axis of the vehicle.

Transverse Engine

An engine fitted across the axis of a motor vehicle.

Trapezoidal

A trapezoid (in North America) or trapezium (in Britain and elsewhere) is a quadrilateral two of whose sides are parallel to each other. Some authors define it as a quadrilateral having exactly one pair of parallel sides, so as to exclude parallelograms. It is the shape made by the linkages in an Ackerman steering system.

Tread (Tire)

The surface of a tire that contacts the road surface and is cut to aid traction and dispel moisture.

Tread (Tyre)

The surface of a tyre that contacts the road surface and is cut to aid traction and dispel moisture.

Tread (Wheel)

The dimension between the centres of the road wheels on one axle. Also known as track.

Trembler

A switch that is operated by movement of a vehicle. Used in alarm system.

Tri-coat

A basecoat, followed by a transparent or translucent mid-coat, followed by clearcoat; to provide a special colour effect on the vehicle.

Tri-pod (Tri-pot) Joint

A constant velocity joint consisting of three drive pins and balls set in three axial tracks.

Trickle Charge

A very slow charge rate for a battery. Usually 1 or 2A overnight.

Trim Height

A measurement taken from a fixed point on the vehicle body to the centre of the wheel.

Trip Computer

A computer built in to some vehicles. It allows the display of different values such as average fuel consumption and estimated time of arrival at a destination.

Trunion

A pivoting assembly consisting of a rod and bearings.

Trunking

General name for large pipes or tubes usually used to carry air.

TSP

Throttle Solenoid Positioner

Tuned Intake Pressure Charging

A system of intake air management that maximizes the flow of air into an engine by using the reciprocating air resonance in the manifold at different engine speeds.

Tungsten

Steel grey heavy metallic element with very high melting point. Used for light bulb filaments.

Turbine

The driven member in a turbocharger, turbine engine and torque converter. The turbine consists of a set of blades on a central boss and shaft and is driven by exhaust gases in a turbocharger or turbine engine and by liquid from the impeller in a torque converter.

Turbocharged

Engine with a turbocharger, which is an exhaust driven device that pumps in extra air.

Turbocharger

Air supply pressure charger driven by the engine's exhaust gas flow.

Turn angle sensor

A device that measures and outputs a signal proportional to the angle that a vehicle is turning.

Turning Centre

An imaginary point about which a vehicle turns when cornering. Also known as the instantaneous centre of turn or rotation.

Turning Circle/Radius

The minimum circle or radius in which a vehicle can turn when on full steering lock.

TV

Throttle Valve

TVS

Thermal Vacuum Switch

TWC

Three way catalyst.

TWC+OC

Three Way + Oxidation Catalytic Converter

Twin Choke Carburettor

A carburettor with two venturis either acting together or progressively.

Two Stroke Cycle

An engine operating on two strokes of the piston. Induction occurs in the crankcase below the piston on the upstroke and is transferred to the cylinder at the end of the down stroke. Compression takes place above the piston on up stroke. The combustion and exhaust strokes occur above the piston on the down stroke.

Two-component System (2K)

Materials such as paints, fillers, and adhesives which require the addition of a hardener or activator to accomplish a chemical reaction, causing them to cure.

Two-tone

Two different colours on a single paint job.

Tyres

Tyres (or 'tires' in American English) are ring-shaped parts, either pneumatic or solid, that fit around wheels to protect them and enhance their function.
U

U Bolts

U shaped bolts used to fix leaf springs to the axle or other similar tasks such as fixing a steering rack to the body.

U/J

Universal Joint.

Ultra Violet

A frequency of light that is above the visible spectrum.

Ultraviolet

Light/Radiation lying in the ultraviolet range; wave lengths shorter than light but longer than X rays i.e. beyond the violet end of the spectrum/rainbow.

Ultraviolet (UV) Light

That portion of the spectrum which is largely responsible for the degradation of paints. It is invisible to the eye and may also be referred to as "black light." Special UV lamps can be used to cure some paints and adhesives.

ULW

Unladen Weight – The weight of a vehicle inclusive of the body and all parts which are ordinarily used with the vehicle when working on a road. Unladen weight does not include the weight of water or fuel used for the propulsion of the vehicle,
or of loose tools and loose equipment.

Unburned Hydrocarbons

Engine or fuel tank emissions in the exhaust gas, fuel line vents or lubricating oil vapours. Harmful to health. Also HC or THC (total hydrocarbon content of exhaust gas).

Under-bake

The result of curing a paint film at too low a combination of time and temperature. The film may be too soft for good durability.

Undercoat

A first coat; primer, sealer, or surfacer applied to the substrate. Frequently used to provide corrosion protection and adhesion.

Understeer

Steering condition of a turning vehicle when the vehicle attempts to turn by a lesser degree than the steered position taken by the driver. This condition is usually provided by vehicle design in order to improve the driveability of the vehicle.

Underwritten

Sign and accept liability (legal).

Unequal Wishbones

Suspension type with an upper wishbone shorter than the lower wishbone. The geometry of this layout keeps the wheel camber reasonably constant during suspension movements. Also SLA suspension.

Unidirectional

Move in one direction only.

Unidirectional Clutch

A clutch, used in starter motors for example, to only allow drive to pass in one direction.

Union Nut

A hollow nut used to secure hydraulic pipes.

Unit-body Construction

Vehicle body and chassis constructed as a single unit. As distinct from a separate chassis and body construction. Also unitary body construction.

Unitary Body Construction

Vehicle body and chassis constructed as a single unit. As distinct from a separate chassis and body construction. Also unit-body construction.

Universal Joints

Rotating shaft coupling that permits angular axial displacement. Some types will also operate with linear misalignment of axes.

Unladen

Not carrying a load.

Unleaded Petrol

Petrol without any added lead to improve the octane rating.

Unsprung Mass

The part of the vehicle not supported by the suspension springs. The road wheels, hubs, brakes and part of the suspension system.

Unsprung Mass (Weight)

The par