Automotive Service Glossary - Houston's Premier Automotive Service Center

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C-clip: part used to retain the axle shaft in a drive axle assembly.

Calibrate: to adjust a tool to achieve accuracy of measurement.

Caliper: see 'disc brake caliper'.

Camber: the attitude of a wheel/tire assembly in which, when viewed from the front, the distant between the tops and bottoms of the tires are different. If the distance between the tops is greater than or is less than between the bottoms, camber is either negative or positive.

Camshaft: a shaft with eccentric lobes that control the opening of the intake and exhaust valves.

Camshaft bearing: a bearing that supports the camshaft journal. On some engines it is full, round and pressed in place. On some OHC engines the camshaft bearing is made up of two shells like a connecting rod bearings.

Camshaft position sensor (CMP): a magnetic, hall effect, optical or magneto resistive sensor usually mounted internally in the engine to inform the ECM or PCM of piston position on the intake stroke for timing and synchronization of sequential fuel injection.

Camshaft sprocket: the sprocket on a camshaft that is turned by a chain or belt from the crankshaft. The camshaft sprocket has twice as many teeth as the crankshaft sprocket.

Carbon: a hard or soft nonmetallic element that forms in an engine's combustion chamber when oil is burned.

Carbon dioxide (CO2): a colorless, odorless, noncombustible gas, heavier than air; can be compressed into a super-cold solid known as dry ice; changes from solid to vapor at -78.5 C. 

Carbon monoxide (CO): a colorless, odorless gas, which is highly poisonous. CO is produced by incomplete combustion. It is absorbed by the bloodstream 400 times faster than oxygen.

Carburetor: a device that atomizes air and fuel in a proportion that is burnable in the engine.

Caster: angle formed between the kingpin axis and vertical axis as viewed from the side of the vehicle. Caster is considered positive when the top of the kingpin axis is behind the vertical axis, that is, tilted toward the rear of the vehicle.

Catalyst: a compound or substance that that can speed up or slow down the reaction of other substances without being consumed itself. In a catalytic converter, special metals (platinum or palladium) are used to promote combustion of unburned hydrocarbons and reduce carbon monoxide.

Catalytic converter: an emissions control device located in the exhaust system that contains catalysts, which reduce hydrocarbons, carbon monoxide and nitrogen oxides in the exhaust gases.

Center link: a steering linkage component which attaches the Pitman arm to the idler arm, tie-rod or crosslink.

Center of gravity: the point in a body or system around which its weight is evenly distributed or balanced; the point of balance.

Centrifugal force: the force which pulls an object outward when it is rotating rapidly around a center axis.

Chafing: damage or wearing caused by friction and rubbing.

Charge: the electrical current that passes through the battery to restore it to full power; to fill, or bring up to the specific level, an A/C system with refrigerant; the required amount of refrigerant for an A/C system.

Charging system: the system that supplies electrical power for vehicle operation and recharges the battery.

Chase: to straighten or repair damage threads, usually with a tap and die.

Check valve: a gate or valve that allows passage of a gas or liquid in one direction only.

Choke: a device used on carbureted vehicles to reduce the amount of air entering the intake manifold while leaving the amount of fuel unchanged. The purpose of a choke is to richen the mixture enough that a cold engine can still get enough vaporized fuel to start.

Circuit: a path through which electricity flows before returning to its source.

Circuit breaker: a device used in an electrical circuit to interrupt current flow in the event of an overload or short.

Closed loop: electronic feedback system in which sensors provide constant information on what is taking place in the engine; the state of the engine control computer system when it is working normally, at full operating temperature and normal speeds with the oxygen sensor switching. The fuel injection quantity is determined by the set of inputs from the engine control computer's sensors, most specifically the oxygen sensor in the exhaust stream. A closed loop system samples its output and uses that sampling to modify the next inputs.

Clutch: in a manual transmission, a device that allows the driver to engage and disengage the engine from the drivetrain; in an automatic transmission, a device capable of both holding and turning members of a planetary gearset; a device used to engage and disengage and A/C compressor.

Clutch cycling switch: a device that opens and closes the circuit that engages the air conditioning compressor clutch based on pressure or temperature.

Clutch disc: the part of a clutch that receives the driving motion from the flywheel and pressure plate assembly and transmits that motion to the transmission input shaft.

Clutch facing: the friction material on a clutch disc.

Clutch fork: also known as the release fork. The device which moves the throwout (release) bearing, activating the pressure plate.

Clutch pack: in an automatic transmission, an assembled series of clutch friction discs and clutch plates that are alternately layered.

Clutch pressure plate: the part of a clutch assembly that is used to hold the driven disc against the flywheel. The pressure plate is composed of a cover and coil springs, driving disc and release levers, or a diaphragm spring.

Clutch release bearing: a sealed ball or roller bearing unit that rides on a sleeve over the transmission input shaft, and acts on the pressure plate to disengage the clutch disc when the clutch release mechanism is applied. Also called a throwout bearing.

Clutch throwout bearing: see 'clutch release bearing'.

Coil spring: spring steel rod wound into a coil that supports the vehicle's weight while allowing suspension movement.

Cold cranking amps: the amount of cranking amperes that a battery can deliver in 30 seconds at 0F. (18C)

Combustion: the burning of air/fuel mixture.

Combustion chamber: enclosure formed by a pocket in the cylinder head and the top of the piston, where the spark plug ignites the compressed air/fuel mixture. The volume of the cylinder above the piston when the piston is at TDC.

Compression: in a solid material, compression is the opposite of tension. In a gas, compression causes the gas to be confined in a smaller area, raising its temperature and pressure.

Compression ratio: ratio of the volume in the cylinder above the piston when the piston is at bottom dead center of the volume in the cylinder above the piston when the piston is at the top dead center.

Compression rings: usually the two rings on a piston, they form a seal between the piston and cylinder wall to compress the air fuel mixture in the cylinder.

Compressor: an engine driven device that compresses refrigerant gas and pumps it through the air conditioning system.

Compressor clutch: Turns the compressor on and off.

Computer: an electrical device that receives information from sensors and makes decisions based on these inputs along with programmed information, and sends out the decisions to actuators.

Condensation: the process of a vapor becoming a liquid; the opposite of evaporation. 

Condense: to cool a vapor below its boiling point, where it then condenses into a liquid.

Condenser: a device, similar to a radiator, in which the refrigerant loses heat and changes state from a high-pressure gas to a high-pressure liquid as it dissipates heat to the surrounding air.

Condenser fan: helps to ensure the optimal liquefaction of the refrigerant no matter what operating state the vehicle is in. It is mounted upstream or downstream of the condenser and/or engine cooling system as an additional or combination fan.

Conductor: a material that provides a path for the flow of electrical current or heat.

Connecting rod: a rod that connects the crankshaft to the piston and enables the reciprocating motion of the piston to turn the crankshaft.

Connecting rod bearings: the plain bearing shells located in the big end of the connecting rod that support the connecting rod and the piston on the crankshaft.

Constant velocity (CV) joint: a flexible coupling between two shafts that allows each shaft to maintain the same speed regardless of operating angle.

Continuous injection: a system that uses fuel under pressure to maintain or change the fuel injection area.

Control arm: a suspension component that connects the vehicle frame to the steering knuckle or axle housing and allows the up and down movement of the wheels.

Coolant: the mixture of water and antifreeze used in an engine's cooling system to maintain the engine's temperature throughout its operating range.

Cooling fan: a mechanically or electronically driven propeller that draws air through the radiator.

Coolant reservoir: a tank used for storing excess coolant; connected to the cooling system with a small-diameter overflow hose.

Cooling system: the system used to remove excess heat from an engine and transfer it to the atmosphere. Includes the radiator, cooling fan, hoses, water pump, thermostat and engine coolant passages.

Corrode: gradual loss from a metal surface from chemical action.

Corrosion: the eating into or wearing away from a substance gradually by rusting or chemical action.

Corrosivity: the characteristic of a material that enables it to dissolve metals and other materials or burn the skin.

Cotter pin: a safety component made from soft steel, used to keep a nut from loosening on bolt or stud. The cotter pin is inserted through a hole in the bolt or stud and through slots in the nut, then the ends of the cotter pin are spread to lock it in position.

Crankcase: the lower part of an engine block that houses the crankshaft.

Crankshaft: a lower engine part with main and rod bearing journals. It converts reciprocating motion to rotary motion.

Crankshaft pulley: the belt drive pulley mounted on the front of the vibration damper.

Crankshaft position sensor (CKP): a magnetic, hall effect, optical or magneto resistive sensor usually mounted internally in the engine, externally to the engine or in the distributor to inform the ECM or PCM of crankshaft position, location No.1 piston, and crankshaft speed for ignition timing and other calculation needed by the system where rpm is an input.

Crossmember: part of the vehicle frame structure, arranged transversely and attached to the frame rails at each side of the vehicle. Can be removable or welded in place.

Cylinder: a round hole in the engine block for the piston.

Cylinder head: the casting that contains the valves and valve springs, and covers the top of the cylinders.

Cylinder leakage test: an engine diagnostic test where the piston in the cylinder to be tested is brought to top dead center (TDC) on the compression stroke and compressed air is pumped into the cylinder through the spark plug hole. Where the air leaks out shows the location of the compression leak. A leakage tester will compare the air leaking out of the cylinder to the amount of air being put into it. Expressed as a percentage.

Cylinder walls: the walls of the cylinder bore.