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C
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.
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.
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 chordwise 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.
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 Monoxide (CO): Polluting, odourless, toxic (poisonous) gas produced by incomplete combustion of fuel.
Carburettor: Device for vaporising liquid fuel and mixing it in appropriate proportions with a stream of air, prior to combustion in an engine.
Cardan
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: Chemical that will increase other chemical reactions without itself being used.
Catalytic Converter: Uses platinum, palladium and rhodium to change pollutants in exhaust gases to harmless substances.
Cathode: A negative connection.
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.
CDI (Ignition): Capacitor discharge ignition system that uses a capacitor to produce the high tension for arcing across the electrodes of the spark plug.
Cell: A single unit of a battery. Consists of positive and negative plates in an electrolyte that can discharge an electrical current when connected to a conductive circuit.
Cell Caps: Removable covers for a battery cell.
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.
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 (Fuel Injection): Usually centre point fuel injection system but sometimes used for continuous fuel injection.
Chaffing: Used to describe the unintentional action of one component rubbing against another.
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.
Chemical Bond: A reaction between atoms that causes a force such as to create a bond.
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.
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.
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.
CKP Sensor: Abbreviation for the crankshaft position sensor.
Clamp Plate: A simple plate to hold another item securely.
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.
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.
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 Sensor: Abbreviation for the camshaft position sensor.
Coasting: Driving on very light throttle at a constant speed.
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-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.
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.
Commutator: Rotating contacts for electrical windings on a generator or motor armature.
Compensator: Provides equal force to mechanically braked wheels.
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.
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 swept volume of a cylinder and the clearance volume above the piston (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.
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.
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.
Connecting Rod: The engine component that joins the piston to the crankshaft.
Constant Velocity
Construction and Use: The UK Construction and Use Regulations that cover the legal requirements on manufacturers and users of road vehicles.
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.
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.
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.
Coolant: Liquid made up of water, anti-freeze and inhibitors used to cool an engine in a sealed but circulated liquid system.
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: Destructive chemical reaction between metal and oxygen.
Corrosive: An acid or other chemical that will chemically react or attack another material.
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.
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 comupter.
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: Describes the process of rotating the engine with the starter motor.
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.
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
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-pin (Hooke’s)
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-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: Maintaining a steady part load vehicle speed.
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.
CT: Closed throttle.
CTS Sensor: Abbreviation for the engine coolant temperature sensor or 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.
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.
Cut-off: Process where fuel supply can be stopped, for example when a vehicle is coasting down.
CV (Constant Velocity)
CV
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.