Glossary of automotive

ABS: Anti-lock braking system. An electro-mechanical braking system which is designed to minimize or prevent wheel lock-up during braking.
ACCELERATOR PUMP: A small pump located in the carburetor that feeds fuel into the air/fuel mixture during acceleration.
ADVANCE: Setting the ignition timing so that spark occurs earlier, before the piston reaches top dead center (TDC).
AFTER TOP DEAD CENTER (ATDC): The point after the piston reaches the top of its travel on the compression stroke.
AIR BAG: Device on the inside of the car designed to inflate on impact of crash, protecting the occupants of the car.
AIR CLEANER: An assembly consisting of a housing, filter and any connecting ductwork. The filter element is made up of a porous paper, sometimes with a wire mesh screening, and is designed to prevent airborne particles from entering the engine through the carburetor or throttle body.

Figure 1 Typical type of air cleaner assembly on most of today's cars

AIR INJECTION: One method of reducing harmful exhaust emissions by injecting air into each of the exhaust ports of an engine. The fresh air entering the hot exhaust manifold causes any remaining fuel to be burned before it can exit the tailpipe.
AIR PUMP: An emission control device that supplies fresh air to the exhaust manifold to aid in more completely burning exhaust gases.
AIR/FUEL RATIO: The ratio of air-to-gasoline by weight in the fuel mixture drawn into the engine.
ALIGNMENT RACK: A special drive-on car lift apparatus/measuring device used to adjust a car's toe, caster and camber angles.
ALL WHEEL DRIVE: Term used to describe a full time four wheel drive system or any other car drive system that continuously delivers power to all four wheels. This system is found primarily on station wagon cars and SUVs not utilized for significant off road use.
ALTERNATING CURRENT (AC): Electric current that flows first in one direction, then in the opposite direction, continually reversing flow.
ALTERNATOR: A device which produces AC (alternating current) which is converted to DC (direct current) to charge the car battery.

Figure 2 Automotive alternator

AMMETER: An instrument, calibrated in amperes, used to measure the flow of an electrical current in a circuit. Ammeters are always connected in series with the circuit being tested.
AMP/HR. RATING (BATTERY): Measurement of the ability of a battery to deliver a stated amount of current for a stated period of time. The higher the amp/hr. rating, the better the battery.
AMPERE: The rate of flow of electrical current present when one volt of electrical pressure is applied against one ohm of electrical resistance.
ANALOG COMPUTER: Any microprocessor that uses similar (analogous) electrical signals to make its calculations.
ANTIFREEZE: A substance (ethylene or propylene glycol) added to the coolant to prevent freezing in cold weather.
ANTI-LOCK BRAKING SYSTEM: A supplementary system to the base hydraulic system that prevents sustained lock-up of the wheels during braking as well as automatically controlling wheel slip.
ANTI-ROLL BAR: See stabilizer bar.

Figure 3. Location of a typical anti-roll bar on a McPherson strut suspension

ANTI-SWAY BAR LINKS: The link pins and bushings that connect the anti-sway bar to the lower control arms in the front or rear suspension.
ARMATURE: A laminated, soft iron core wrapped by a wire that converts electrical energy to mechanical energy as in a motor or relay. When rotated in a magnetic field, it changes mechanical energy into electrical energy as in a generator.
ASE: Acronym for the National Institute for Automotive Service Excellence. ASE is usually affiliated with being a Certified Technician. ASE provides a testing system to recognize a technicians skills and abilities in specific mechanical areas, such as drivetrain, engine performance, electrical, etc.
ATDC: After top dead center.
ATF: Automatic transmission fluid.
ATMOSPHERIC PRESSURE: The pressure on the Earth's surface caused by the weight of the air in the atmosphere. At sea level, this pressure is 14.7 psi at 32°F (101 kPa at 0°C).
ATOMIZATION: The breaking down of a liquid into a fine mist that can be suspended in air.
AWD: All wheel drive.
AXIAL PLAY: Movement parallel to a shaft or bearing bore.
AXLE CAPACITY: The maximum load-carrying capacity of the axle itself, as specified by the manufacturer. This is usually a higher number than the GAWR.
AXLE RATIO: This is a number (3.07:1, 4.56:1, for example) expressing the ratio between driveshaft revolutions and wheel revolutions. A low numerical ratio allows the engine to work easier because it doesn't have to turn as fast. A high numerical ratio means that the engine has to turn more rpm's to move the wheels through the same number of turns.
BACKFIRE: The sudden combustion of gases in the intake or exhaust system that results in a loud explosion.
BACKLASH: The clearance or play between two parts, such as meshed gears.
BACKPRESSURE: Restrictions in the exhaust system that slow the exit of exhaust gases from the combustion chamber.
BAKELITE: A heat resistant, plastic insulator material commonly used in printed circuit boards and transistorized components.
BALL BEARING: A bearing made up of hardened inner and outer races between which hardened steel balls roll.
BALL JOINT: A ball and matching socket connecting suspension components (steering knuckle to lower control arms). It permits rotating movement in any direction between the components that are joined.

Figure 4 Front suspension ball joints

BALLAST RESISTOR: A resistor in the primary ignition circuit that lowers voltage after the engine is started to reduce wear on ignition components.
BATTERY: A direct current electrical storage unit, consisting of the basic active materials of lead and sulphuric acid, which converts chemical energy into electrical energy. Used to provide current for the operation of the starter as well as other equipment, such as the radio, lighting, etc.

Figure 5 A sealed type battery

BEAD: The portion of a tire that holds it on the rim.
BEARING: A friction reducing, supportive device usually located between a stationary part and a moving part.
BEFORE TOP DEAD CENTER (BTDC): The point just before the piston reaches the top of its travel on the compression stroke.
BELTED TIRE: Tire construction similar to bias-ply tires, but using two or more layers of reinforced belts between body plies and the tread.
BEZEL: Piece of metal surrounding radio, headlights, gauges or similar components; sometimes used to hold the glass face of a gauge in the dash.
BIAS-PLY TIRE: Tire construction, using body ply reinforcing cords which run at alternating angles to the center line of the tread.
BI-METAL TEMPERATURE SENSOR: Any sensor or switch made of two dissimilar types of metal that bend when heated or cooled due to the different expansion rates of the alloys. These types of sensors usually function as an on/off switch.
BLOCK: See Engine Block.
BLOW-BY: Combustion gases, composed of water vapor and unburned fuel, that leak past the piston rings into the crankcase during normal engine operation. These gases are removed by the PCV system to prevent the buildup of harmful acids in the crankcase.
BOOK TIME: See Labor Time.
BOOK VALUE: The average value of a car, widely used to determine trade-in and resale value.
BORE: Diameter of a cylinder.
BRAKE CALIPER: The housing that fits over the brake disc. The caliper holds the brake pads, which are pressed against the discs by the caliper pistons when the brake pedal is depressed.

Figure 6 Disc brake

BRAKE FADE: Loss of braking power, usually caused by excessive heat after repeated brake applications.
BRAKE HORSEPOWER: Usable horsepower of an engine measured at the crankshaft.
BRAKE PAD: A brake shoe and lining assembly used with disc brakes.
BRAKE PROPORTIONING VALVE: A valve on the master cylinder which restricts hydraulic brake pressure to the wheels to a specified amount, preventing wheel lock-up.
BRAKE SHOE: The backing for the brake lining. The term is, however, usually applied to the assembly of the brake backing and lining.
BREAKER POINTS: A set of points inside the distributor, operated by a cam, which make and break the ignition circuit.
BTDC: Before top dead center.
BUSHING: A liner, usually removable, for a bearing; an anti-friction liner used in place of a bearing.
CALIFORNIA ENGINE: An engine certified by the EPA for use in California only; conforms to more stringent emission regulations than Federal engine.
CALIPER: A hydraulically activated device in a disc brake system, which is mounted straddling the brake rotor (disc). The caliper contains at least one piston and two brake pads. Hydraulic pressure on the piston(s) forces the pads against the rotor.
CAMBER: One of the factors of wheel alignment. Viewed from the front of the car, it is the inward or outward tilt of the wheel. The top of the tire will lean outward (positive camber) or inward (negative camber).

Figure 7. Camber angle (front view)

CAMSHAFT: A shaft in the engine on which are the lobes (cams) which operate the valves. The camshaft is driven by the crankshaft, via a belt, chain or gears, at one half the crankshaft speed.
CANCER: Rust on a car body.
CAPACITOR: A device which stores an electrical charge.
CARBON MONOXIDE (CO): A colorless, odorless gas given off as a normal byproduct of combustion. It is poisonous and extremely dangerous in confined areas, building up slowly to toxic levels without warning if adequate ventilation is not available.
CARBURETOR: A device, usually mounted on the intake manifold of an engine, which mixes the air and fuel in the proper proportion to allow even combustion.
CASTER: The forward or rearward tilt of an imaginary line drawn through the upper ball joint and the center of the wheel. Viewed from the sides, positive caster (forward tilt) lends directional stability, while negative caster (rearward tilt) produces instability.

Figure 8. Caster angle (side view)

CATALYTIC CONVERTER: A device installed in the exhaust system, like a muffler, that converts harmful byproducts of combustion into carbon dioxide and water vapor by means of a heat-producing chemical reaction.
CENTRIFUGAL ADVANCE: A mechanical method of advancing the spark timing by using flyweights in the distributor that react to centrifugal force generated by the distributor shaft rotation.
CETANE RATING: A measure of the ignition value of diesel fuel. The higher the cetane rating, the better the fuel. Diesel fuel cetane rating is roughly comparable to gasoline octane rating.
CHECK ENGINE LIGHT: The malfunction indicator light that the vehicle's on board computer illuminates when it senses a fault in a monitored system.
CHECK VALVE: Any one-way valve installed to permit the flow of air, fuel or vacuum in one direction only.
CHOKE: The valve/plate that restricts the amount of air entering an engine on the induction stroke, thereby enriching the air:fuel ratio.
CIRCLIP: A split steel snap ring that fits into a groove to hold various parts in place.
CIRCUIT BREAKER: A switch which protects an electrical circuit from overload by opening the circuit when the current flow exceeds a pre-determined level. Some circuit breakers must be reset manually, while most reset automatically.
CIRCUIT: Any unbroken path through which an electrical current can flow. Also used to describe fuel flow in some instances.
CLEARCOAT: A transparent layer which, when sprayed over a car's paint service, adds gloss and depth as well as an additional protective coating to the finish.
CLUTCH: Part of the power train used to connect/disconnect power to the rear wheels.

Figure 9 Exploded view of typical clutch

COIL: Part of the ignition system that boosts the relatively low voltage supplied by the car's electrical system to the high voltage required to fire the spark plugs.
COMBINATION MANIFOLD: An assembly which includes both the intake and exhaust manifolds in one casting.
COMBINATION VALVE: A device used in some fuel systems that routes fuel vapors to a charcoal storage canister instead of venting them into the atmosphere. The valve relieves fuel tank pressure and allows fresh air into the tank as the fuel level drops to prevent a vapor lock situation.
COMBUSTION CHAMBER: The part of the engine in the cylinder head where combustion takes place.
COMPRESSION CHECK: A test involving removing each spark plug and inserting a gauge. When the engine is cranked, the gauge will record a pressure reading in the individual cylinder. General operating condition can be determined from a compression check.

Figure 10 Performing a compression check using a compression gauge

COMPRESSION RATIO: The ratio of the volume between the piston and cylinder head when the piston is at the bottom of its stroke (bottom dead center) and when the piston is at the top of its stroke (top dead center).
CONDENSER: 1. An electrical device which acts to store an electrical charge, preventing voltage surges. 2. A radiator-like device in the air conditioning system in which refrigerant gas condenses into a liquid, giving off heat.
CONDUCTOR: Any material through which an electrical current can be transmitted easily.
CONNECTING ROD: The connecting link between the crankshaft and piston.
CONSTANT VELOCITY JOINT: Type of universal joint in a halfshaft assembly in which the output shaft turns at a constant angular velocity without variation, provided that the speed of the input shaft is constant.
CONTINUITY: Continuous or complete circuit. Can be checked with an ohmmeter.
CONTROL ARM: The upper or lower suspension components which are mounted on the frame and support the ball joints and steering knuckles.
CONVENTIONAL IGNITION: Ignition system which uses breaker points.
COOLANT: Mixture of water and anti-freeze circulated through the engine to carry off heat produced by the engine.
COUNTERSHAFT: An intermediate shaft which is rotated by a mainshaft and transmits, in turn, that rotation to a working part.
CRANKCASE: The lower part of an engine in which the crankshaft and related parts operate.
CRANKSHAFT: Engine component (connected to pistons by connecting rods) which converts the reciprocating (up and down) motion of pistons to rotary motion used to turn the driveshaft.
CURB WEIGHT: The weight of a car without passengers or payload, but including all fluids (oil, gas, coolant, etc.) and other equipment specified as standard.
CV-JOINT: Constant velocity joint.
CYLINDER BLOCK: See engine block.

Figure 11. Basic cylinder block (engine block) casting

CYLINDER HEAD: The detachable portion of the engine, usually fastened to the top of the cylinder block and containing all or most of the combustion chambers. On overhead valve engines, it contains the valves and their operating parts. On overhead cam engines, it contains the camshaft as well.