Automotive Dictionary ABBREVIATIONS brake horsepower: bhp horsepower: hp kilometers per hour: kph miles per hour: mph cubic centimeter: cc millimeter: mm overhead camshaft: OHC overhead valve: OHV revolutions per minute: rpm cubic inch: cu. in. ANTILOCK BRAKING SYSTEM (ABS) A system used to prevent tire skid during heaving braking in low traction situations. AC CONTROL UNIT An electrical system that controls the operation of the AIR CONDITIONING SYSTEM. In most newer cars this includes an ECM. ACCESSORIES The collection of components connected to the engine. They include: ALTERNATOR, AC COMPRESSOR, STEERING PUMP, WATER PUMP, AIR PUMP. ACCUMULATOR (AIR CONDITIONING) A component of the AC SYSTEM that filters and dries the FREON. AERODYNAMICS Describe the way air flows around the automobile while in motion. Better aerodynamics will generally mean better fuel economy and high speed performance. AIR BAG A device that inflates during an accident to protect the vehicle passengers. Usually triggered by extreme changes in vehicle velocity or structural damage to the front, rear, or sides of the vehicle. AIR CLEANER Contains the AIR FILTER. Usually located on top of or directly beside the engine. On new cars this is a black plastic box. AIR CONDITIONING (AC) SYSTEM A system that cools the air flowing into the passenger compartment of the vehicle. Includes a compressor, condenser core, evaporator core, accumulator, AC control unit, and freon. The freon is compressed from a gas to a liquid in the compressor. This adds energy to the freon and it becomes very hot. It then travels to the condenser core where it is cooled by the COOLING SYSTEM air and the energy is removed from the liquid freon. It then travels to the evaporator core where it evaporates from a liquid to a gas. Here the freon absorbs energy from the HVAC air and cools it. This is the cool air you feel coming out of the vents. The gas freon then travels through the accumulator and back to the compressor for another cycle. AUTO STAMPING PLANT A facility that presses a steel blank into the desired form of a car door or hood, for example, with a powerful die (pattern). The steel used must be ductile (malleable) enough to bend into shape without breaking. AIR-FUEL MIXTURE The combination of air and fuel that is ignited in the COMBUSTION CHAMBER. AIR FILTER Located in the AIR CLEANER. Cleans or filters the air going into the engine. Should be changed regularly to ensure proper operation. AIR INJECTION REACTION (AIR) SYSTEM Part of the EMISSIONS SYSTEM. It generally contains an AIR PUMP, control valve, check valve, and the CATALYTIC CONVERTER. The air pump forces fresh air into either the EXHAUST MANIFOLD, INTAKE MANIFOLD, or the catalytic converter. AIR PUMP Part of the AIR SYSTEM. Usually located near the front of the engine and is driven by the BELT DRIVE. ALIGNMENT The relationship of the WHEELS to the SUSPENSION and the road surface. Improper alignment can affect steering performance and increase TIRE wear. The alignment should be adjusted periodically and whenever new tires or suspension components are installed. ALTERNATOR Part of the CHARGING SYSTEM. Usually mounted to the engine and driven by the BELT DRIVE. ANTIFREEZE Part of the COOLING SYSTEM. Also known as engine COOLANT. Usually Green in color. Can be corrosive to paint finishes and toxic to humans and animals. AUTOMATIC TRANSMISSION A type of TRANSMISSION that shifts its own gears according to the current speed, load, and road condition. Operation can be electrical or hydraulic. Contains a TORQUE CONVERTER, several CLUTCHES, and a series of GEARS. Operation of the clutches (and gear selection) is automatic. Usually contains 3,4 or 5 gears as well as a reverse gear. AXLE Part of the DRIVE TRAIN. Most vehicles contain both a front and rear axle. Holds the WHEELS to the CHASSIS and allows them to spin. B BALL JOINT A component of the STEERING SYSTEM that connects the RACK AND PINION or GEAR BOX to the AXLE. BATTERY A component of the CHARGING SYSTEM. Most automotive batteries are made of lead plates submerged in and acid solution. BEARING A device that supports a shaft to reduce friction. Places where bearing are found include: AXLE shafts, ALTERNATORS, COMPRESSORS, CRANKSHAFTS, and CAM SHAFTS. BELT A component of a BELT DRIVE. Usually made of synthetic rubber. They come in many forms: V belts, serpentine belts, cog belts. V belts were used on most older automobiles that have a belt for each accessory and have a single V shape. Serpentine belts are used on most newer automobiles and have a multiple V shape. Cog belts are used on most TIMING BELT DRIVES and have flat shape with a series of teeth that engage in similar teeth on the PULLEY. BELT DRIVE A system that consists of a series of PULLEYS and BELTS. On an automobile the belt drive connects the CRANKSHAFT to the ACCESSORIES. BLOCK A component of the ENGINE. Houses the CRANKSHAFT, PISTONS, CONNECTING RODS, OIL PUMP, WATER PUMP and sometimes the CAM SHAFT. Made of cast iron or aluminum. BLOWER MOTOR A Component of the HVAC SYSTEM. Located under the dash or in the engine compartment mounted to the FIREWALL. Blows air into the passenger compartment. BOOSTER CABLES Also know as jumper cables. Used to connect one vehicle BATTERY to another to aid in starting. Contains Black (negative) and Red (positive) leads. BORE The approximate diameter of the engine PISTONS. The engine DISPLACEMENT can be increased by increasing the diameter ("boring out" or "over boring"). BRAKE BOOSTER A component of the BRAKE SYSTEM. Uses engine intake VACUUM to increase the pressure from the brake pedal to the MASTER CYLINDER. BRAKE CALIPER See CALIPER. BRAKE FLUID A very tough and durable plastic material with fibers running through the plastic. Used for race car bodies, many sports car bodies, and also enjoys considerable acceptance for passenger car bodies. BRAKE PAD A component of the BRAKE SYSTEM. Used on systems with DISC BRAKES. BRAKE SHOE A component of the BRAKE SYSTEM. Used on systems with DRUM BRAKES. BRAKE HORSEPOWER (BHP) The measure of an engine's horsepower at the CRANKSHAFT. Without the loss in power caused by the gearbox, generator, differential, water pump and other auxiliaries. The actual horsepower delivered to the driving wheels is less. BRAKE SYSTEM The collection of components used to stop the vehicle. Includes the MASTER CYLINDER, SLAVE CYLINDER, EQUALIZING VALVE, CALIPERS, PADS or SHOES, ROTORS or DRUMS, and BRAKE FLUID. When the brake pedal is depressed, the master cylinder applied pressure to the brake fluid. The fluid in turn applies pressure to the calipers. This forces the pads or shoes up against the drums or rotors and caused the automobile to slow down or stop. C CABRIOLET An automobile with collapsible top (convertible) and seating two or four passengers. CALIPER A component of the BRAKE SYSTEM. Consists of a cast iron or aluminum housing and a piston. Houses the BRAKE PADS on DISC BRAKE systems. There is one caliper for each WHEEL. Most caliper can be easily rebuilt. Factory rebuilt replacements are also available. CAM An eccentric (off-center) lobe or projection on a rotating shaft; used to transmit a motion at a predetermined time during the rotation of the shaft. CAMSHAFT A rotating shaft with a number of cams or eccentric lobes used to operate the engine valves, usually via pushrods and rocker arms. CARBURETOR A device through which air and fuel are drawn into the engine. It meters the proper proportions of fuel and air to form a combustible mixture and varies the ratio according to the engine operation. CATALYTIC CONVERTER A component of the EMISSIONS SYSTEM. Located under the vehicle, the exhaust gas flows through the converter. Harmful emission gases (carbon monoxide and hydrocarbons) are converted to harmless carbon dioxide and water vapor. CHARGING SYSTEM Used to provide electrical power to the engine and accessories. Consists of a BATTERY, and ALTERNATOR. CHASSIS i.e. a car without its body or coachwork. CHOKE A temporary restriction in a carburetor throat that reduces the flow of air and enriches the fuel-air mixture to aid in starting the engine. Used only on older automobile with CARBURETORS. CLUTCH A friction device used to connect one component to the other. One example is the engine to the transmission. This is used when changing gears. When the clutch is depressed, the engine is disconnected from the transmission. Another example is the AC COMPRESSOR clutch. This is used to engage and disengage the BELT DRIVE from the AC compressor as needed. Operation of this clutch is controlled by the AC CONTROL UNIT. COIL See IGNITION COIL. COMBUSTION CHAMBER The space at the top of the CYLINDER when the PISTON is at the top dead center (TDC) position. Where the fuel-air mixture begins to burn. COMPRESSION The pressurizing of the fuel-air mixture in the CYLINDER of a SPARK-IGNITION engine or the pressurizing of the air in a COMPRESSION-IGNITION (DIESEL) engine. Compression makes combustion more effective and increases engine efficiency. A worn engine will have lower compression than a new one. COMPRESSION-IGNITION An engine in which the fuel-air mixture is ignited by means of compression. The most common type is the DIESEL ENGINE. COMPRESSION RATIO The ratio of the cylinder volume with the piston at bottom dead center to the cylinder volume with the piston at TOP DEAD CENTER. COMPRESSION RING The upper ring(s) around the PISTON that seal the CRANKCASE from the COMBUSTION CHAMBER and prevent loss of compression. COMPRESSOR (AIR CONDITIONING) A component of the AIR CONDITIONING SYSTEM. It compresses the gaseous FREON into liquid form. Usually mounted to the engine and driven by the BELT DRIVE. It includes an electric CLUTCH that engages and disengages the compressor. CONDENSER CORE A component of the AIR CONDITIONING SYSTEM. It is usually mounted ahead of the RADIATOR and looks like a miniature version of it. CONNECTING ROD The arm that connects the PISTON to the CRANKSHAFT and converts the reciprocating motion into rotary motion. CONVERTIBLE Any car with a folding roof. The hardtop convertible looks like a convertible but has a fixed roof that does not fold. CONVERTIBLE SEDAN Any car that has 4 doors and a folding top with roll-up windows. COOLING FAN A component of the COOLING SYSTEM. Used to pull or push air through the RADIATOR. Either driven by the BELT DRIVE or and electric motor. COOLING SYSTEM Used to cool or remove heat from the engine. Consists of the RADIATOR, WATER PUMP, COOLING FAN, THERMOSTAT and ANTIFREEZE.. COOLANT See ANTIFREEZE. COUPE Originally meant a vehicle "cut" by a glass partition behind the front seats that enabled the rear passengers to ride enclosed and the driver exposed. Today, a two-to-five-seater with smaller interior than a sedan. Usually a sporty type. COWL Part of a car's body between the engine compartment and the driver. CRANKCASE A pan or box that encloses the bottom of the engine, supports the crankshaft, and contains the oil for the engine. The lower part of the BLOCK. CRANKSHAFT The main shaft of an engine with a U-shaped offset at each cylinder. The connecting rods are attached to the crankshaft. It delivers rotary motion taken from the reciprocating pistons and connecting rods. CUBIC CENTIMETER (CC) European, metric, and competition measure of engine displacement: 1,000 cc = 1 liter, which equals about 61 cubic inches. CUBIC INCH (CU. IN or CID) U.S. measure of engine displacement: 1 cubic inch = 16.387 cc. CYLINDER The hollow tubular cavity in the cylinder BLOCK in which the PISTON travels and in which combustion takes place. CYLINDER HEAD The detachable part of the top of the cylinder BLOCK that contains the SPARK PLUGS and VALVES. It seals the cylinder and forms the top of the COMBUSTION CHAMBER. D DIESEL ENGINE An COMPRESSION-IGNITION engine in which the fuel is injected into the cylinder near the end of the compression stroke and is ignited by the heat of the compressed air in the cylinder. No SPARK PLUGS or CARBURETOR is needed. DIFFERENTIAL GEARS The gears that transfer engine power to the driving axles and are arranged so as to permit the rear wheels to turn at different speeds as required when the vehicle is negotiating a turn. DISC BRAKES A type of brake in which two friction PADS grip a steel ROTOR that is attached to the wheel, with one pad on each side. Used on race cars, sports cars, and better passenger cars. DISTRIBUTOR The moving part of the engine IGNITION SYSTEM that directs the high-voltage current from the COIL to the SPARK PLUGS in the proper firing order. DISPLACEMENT The total volume of all CYLINDERS of on engine. Measured in CC (L) or CID. DRIVE TRAIN The combination of engine, TRANSMISSION, CLUTCHES, and DIFFERENTIAL GEARS, etc., that transmits the engine power to the wheels. DRUM A component of the BRAKE SYSTEM. Used primarily on the rear wheels of cheaper automobiles. Uses BRAKE SHOES. Can usually be TURNED when replacing the brakes. DRUM BRAKES A type of brake that uses DRUM brakes. Usually found on the rear wheels of cheaper automobiles. DRY SUMP Type of internal-combustion engine in which the lubricating oil is stored either in a separate tank or cooling radiator instead of in the crankcase pan. The oil is pumped to and taken from the engine by separate pumps. DWELL ANGLE The number of degrees of DISTRIBUTOR rotation through which the breaker POINTS remain fully closed. Applies only to older vehicles with point ignition systems. Increased point gap = decreased dwell angle, while decreased point gap = increased dwell angle. E ECM (ELECTRONIC CONTROL MODULE) The central component of the ELECTRICAL SYSTEM. The ECM is the "brain" or "computer" of the car. It take electrical inputs from all the sensors and controls of the car and translates them into outputs sent to other systems of the car. ELECTRICAL SYSTEM In electric ignition internal-combustion engines, those components required to convert the electricity produced by the generator into a high-voltage spark for the plugs. Includes: generator or alternator, points, condenser, coil, distributor and spark plugs plus wiring. EMISSIONS SYSTEM A component of the AIR CONDITIONING SYSTEM. It is usually mounted ahead of the RADIATOR and looks like a miniature version of it. ENGINE Main power source of the automobile. ENGINE TYPES V10, V8, V6, I6, I4. V means the CYLINDERS are oriented in a "V" pattern. The following number indicates the number of cylinders. SOHC Single overhead CAMSHAFT. DOHC Double overhead CAMSHAFTS. EQUALIZING VALVE A component of the BRAKE SYSTEM. A valve the regulates brake line pressure between the front and rear brakes. The usual split is 60% front, 40% rear. Also called PROPORTIONING VALVE. ELECTRONIC SPARK CONTROL (ESC) EVAPORATOR CORE A component of the AIR CONDITIONING SYSTEM. It is usually mounted under the dash. Looks like a miniature version of the RADIATOR. EXHAUST The system of exhausting the burned gases from an internal-combustion engine consisting of piping or tubing, silencers, and, at times, resonators. EXHAUST EMISSIONS Gases present in the engine EXHAUST that are determined to be detrimental to the environment. These include CO, NOx, and Hydrocarbons. EXHAUST MANIFOLD A component connected to the engine that connects the CYLINDERS to the EXHAUST pipes. The exhaust gases flow from the cylinders to the exhaust pipe through the manifold. F FIBERGLASS A very tough and durable plastic material with fibers running through the plastic. Used for race car bodies, many sports car bodies, and certain performance passenger car bodies. FIREWALL The structural portion of the CHASSIS that divides the engine compartment from the passenger compartment. FLYWHEEL A large, heavy iron or steel disc attached to the rear of the engine CRANKSHAFT in order to provide sufficient centrifugal force to smooth the power impulses from the cylinders. FOUR-STROKE CYCLE An internal-combustion engine that requires two revolutions per CYLINDER or four PISTON strokes to achieve a power stroke: internal stroke, compression stroke, power stroke, exhaust stroke. More efficient than the two-stroke-cycle engine. FRAME A bridge-like, structural base of a car that supports and positions the body and major mechanical items. FREON A component of the AC SYSTEM. A chemical that is in a gas form at normal atmospheric temperatures. Older automobiles use R-12 Freon. R-12 is said to deplete the Ozone layer of the atmosphere. All newer automobiles use environmentally-safe R-134a. FUEL INJECTION On internal-combustion engines, a system that injects a precisely measured amount of fuel into the CYLINDER at exactly the right moment. Fuel injected automobiles do not have CARBURETORS and usually have increased engine efficiency (fuel economy). FUEL RAIL Carries fuel to the INJECTORS. G GASKET A component made of rubber, cork or paper that is placed between two surfaces to create a seal. GEARS Wheels with meshing teeth to transmit power between rotating shafts. When the gear wheels are of different sizes, a change in speed ratio occurs. Gears are made of hard steel. GEAR BOX A collection of GEARS in a common location that mesh together to transfer power. GLOW PLUG A device used to aid in starting diesel (COMPRESSION-IGNITION) engines. Ground An electrical conductor used as a common return for electricity in an electric circuit. H HALF SHAFT A rotating shaft that transmits power from the final drive unit (differential) to a power wheel. Used in independent rear suspension and front-wheel drive. Two are required; one for each side. HELICAL GEAR A GEAR in which the teeth are cut at an angle to the shaft. The advantage is that there are usually two teeth meshing at all times, making for smoother and quieter operation. HEMI Slang term for an engine with hemispherical combustion chambers which allow for larger and less shrouded valves. Used in many sports and racing cars. HEMI-HEAD A hemispherical shaped combustion chamber at the top of the engine cylinder. The hemispheric shape provides improved efficiency because the forces of the explosion are directed to the piston by the curved surface of the combustion chamber. HOOD The removable or lift-up part of an auto body that covers the engine and allows access to it. HORSEPOWER (HP) The unit for measuring the power output of an engine. One horsepower is defined as lifting 33,000 pounds one foot per minute. HVAC SYSTEM Heating, ventilation, and air conditioning system. A general term used to define the components that control the climate inside the passenger compartment of the automobile. HYDRAULIC A mechanical operation based on incompressibility of liquids, generally oil and sometimes water, and their ability to offer resistance when being forced into a small cylinder or through an orifice, thereby transmitting an increase in applied force. Hydraulic brakes and clutches use this principle. HYDRAULIC VALVE LIFTER A LIFTER that uses hydraulic oil pressure to operate. Capable of maintaining zero clearance between metal parts. Thus, valve noise and wear are considerably reduced and the periodic valve adjustments are not necessary. HYPOID GEARS A type of differential final drive using a spiral bevel gear on the drive shaft, allowing it to be located below the center of the ring gear on the axle. This makes possible a lower floor in the car. I IDLE Speed of the engine without accelerator pedal depressed. Ignition Advance/Retard Timing of the ignition spark relative to the position of the PISTIONS. IGNITION COIL A component of the IGNITION SYSTEM. Stores electrical energy from the BATTERY until it is released to the spark plugs through the DISTRIBUTOR. IGNITION MODULE A component of the IGNITION SYSTEM. Used to regulate the spark at the SPARK PLUGS. IGNITION SYSTEM The collection of components used to produce combustion in SPARK-IGNITION engines. Generally includes the BATTERY, IGNITION MODULE, DISTRIBUTOR, and SPARK PLUGS. INDEPENDENT SUSPENSION Suspension in which each wheel is sprung individually so that any disturbance on the wheel has no effect on the opposite wheel. Injector A component of the FUEL INJECTION. A device for delivering fuel to the cylinders. INLINE ENGINE An engine having the cylinders in a straight line, one after the other. Also called a "straight" engine. INTAKE MANIFOLD A component attached to the CYLINDER HEAD. Directs air into each cylinder. Usually houses the CARBURETOR or FUEL INJECTORS. INTERNAL-COMBUSTION ENGINE Any engine, either reciprocating or rotary, in which the fuel is consumed in the interior of the engine rather than outside of the engine. J K Keepers Devices used to hold VALVE RETAINERS in place on the VALVE STEM. L LEAF SPRINGS A component of the SUSPENSION. Several slightly curved, flexible steel plates mounted together. The ends are attached to the CHASSIS, and the middle is fixed to the AXLE. LIFTER A component of the VALVE TRAIN. Connects the CAMSHAFT to the PUSHRODS or ROCKER ARMS. LIMITED SLIP DIFFERENTIAL A differential that uses cone or disc CLUTCHES to lock the two separate AXLE shafts. This forces both driving wheels to transmit the same drive torque regardless of the traction available. It still allows differential action under normal driving conditions but improves traction in mud and snow. M McPherson strut A type of suspension having a shock absorber mounted directly below the coil spring. MAIN BEARINGS BEARINGS that support the CRANKSHAFT in the engine BLOCK. MANIFOLD A component mounted to the CYLINDER HEAD that direct are in and out of the engine. There are two types of manifolds on an engine: INTAKE and EXHAUST. MANUAL TRANSMISSION A type of TRANSMISSION. It consists of a lever that the driver operates in conjunction with the CLUTCH to manually change from one GEAR to another. MASTER CYLINDER A component of the BRAKE SYSTEM. Mounted to the BRAKE BOOSTER, applies pressure to the BRAKE FLUID when the brake pedal is depressed. N NATURALLY ASPIRATED An engine without a supercharger or turbocharger. O ON BOARD DIAGNOSTIC (OBD) A system used to detect and log problems with the automobile. Stores "trouble codes" that can tell a mechanic what may be malfunctioning when the "check engine" light comes on. Usually includes a connector used to hook up a diagnostic computer or scan tool. OIL PUMP An engine-driven pump that delivers oil, under pressure, to the engine's moving parts. OIL RING The lowermost ring around the PISTON that scrapes excess oil from the cylinder walls and returns it to the oil pan. OVERDRIVE An additional gear ratio in the TRANSMISSION. It causes the drive shaft to turn faster than the engine. OVERHEAD VALVE An engine configuration where the VALVES are located in the CYLINDER HEAD above the PISTONS. P PETCOCK Located at the bottom of the radiator. Used to drain the engine COOLANT. PINION A small diameter GEAR with a small number of teeth designed to mesh with a much larger RING gear or a toothed rod (rack). Used in rack-and-pinion steering and for speed reduction with an increase in power. POINTS A component of the IGNITION SYSTEM. Used only on older cars, the points are located in the DISTRIBUTOR and control the timing of the spark at the SPARK PLUGS. PISTON A partly hollow, cylindrical metal engine part that is closed at one end and fits into the engine CYLINDER. Connected to the crankshaft via the connecting rod and usually fitted with RINGS to seal it in the cylinder. PISTON RING See RINGS. PORTING Enlarging the exhaust and intake passages to increase flow through the cylinder heads. Generally increasing the engine HORSEPOWER. POSI See limited-slip differential. Pressure Plate A part of a manual CLUTCH that is mounted on and rotates with the flywheel and exerts pressure against the friction disk. PROPORTIONING VALVE See EQUALIZING VALVE. PULLEY A component of BELT DRIVE systems. Used to connect the belt to the drive or driven shaft. PUSHROD A metal rod connecting the valve LIFTER or CAMSHAFT with the valve ROCKER ARM on OVERHEAD VALVE engines. Q R RACK-AND-PINION STEERING A steering system having a PINION gear at the lower end of the steering column that engages a rack or a toothed rod that connects to the wheel steering arms. RADIAL PLY A tire in which the fabric or steel cords run radially in a line from the wheel hub or straight out from the bead or around the tubular shape of the tire. Annular belts of fabric or steel mesh add rigidity. RADIATOR A component of the COOLING SYSTEM. It is usually mounted directly behind the front bumper. It is built from a lot of metal fins and tubes and is usually black. RECIPROCATING ASSEMBLY Refers to the CRANKSHAFT, CONNECTING RODS, and PISTONS of an engine. RELAY A device in which connections in one circuit are opened or closed by changes in another circuit. Often used to control fuel pumps, lights, and other electrical components. RIMS Steel or aluminum components that mount the TIRES to the AXLES. RINGS See OIL ring and COMPRESSION ring. RING GEAR One of the gears in the rear axle that transmits power to the differential from the drive shaft. ROLLER CAM A CAMSHAFT that has small rollers at the base of each LIFTER. ROCKER ARM A pivoted lever that transmits the action of the pushrod to the valve stem. (Pushrod upward action is converted to downward push on the valve stem. ) ROTOR (IGNITION) A component of the IGNITION SYSTEM. Residing in the DISTRIBUTOR, it rotates in relation to the engine RPM and "distributes" the electrical current to each of the SPARK PLUGS. ROTOR (BRAKE) A component of the BRAKE SYSTEM. Used on vehicles with DISC brakes, the rotor is a metal disc that the BRAKE PADS apply pressure to in order to stop the automobile. S S.A.E. ( Society of Automotive Engineers) A professional organization that publishes technical papers and various standards. SHOCK ABSORBERS A component of the SUSPENSION system. Used to absorb the energy that the wheels convey to the springs. The shocks keep the springs from continuously rebounding. SLAVE CYLINDER A component of the BRAKE SYSTEM. Transfers the pressure from the BRAKE FLUID to the brake PADS or SHOES. SPARK-IGNITION A type of engine in which the fuel-air mixture is ignited by electrical spark. All automobiles that use gasoline are of this type. SPARK KNOCK A repetitive metallic sound coming from the engine. Usually caused by over-advanced timing, poor fuel, or worn-out engine components. SPARK PLUG A device inserted into the combustion chamber of a cylinder on an internal-combustion engine that provides the electrical gap across which the high-tension voltage jumps. This creates a spark that ignites the compressed AIR-FUEL MIXTURE. STEERING PUMP A pump used to amplify the force applied to the steering wheel to aid in steering. Usually mounted to the engine and driven by the BELT DRIVE. STROKE Refers to the back-and-forth motion of the PISTON. The length of the motion of the piston from top dead center to bottom dead center. SUPERCHARGER An air compressor fitted to an internal combustion engine that forces the fuel-air mixture into the CYLINDERS at a pressure greater than that of the atmosphere. Increases the power of the engine. SUSPENSION A system that includes springs, shock absorbers, torsion bars, joints, arms, etc., that cushions the shock of bumps on the road and serves to keep the wheels in constant contact with the road, thereby improving control and traction. SWING AXLE Type of independent rear SUSPENSION using half shafts that have universal joints only at their inboard ends on both sides of the DIFFERENTIAL. This causes a camber angle change of the wheel with up-and-down wheel movements. T TACHOMETER An instrument that indicates the number of revolutions per minute (RPM) at which the engine is turning. THERMOSTAT A component of the COOLING SYSTEM. Used to regulate the flow of COOLANT from the engine. Thermostats have a temperature rating that indicates the temperature at which they open and allow flow. TIMING BELT DRIVE A BELT DRIVE that connects the CRANKSHAFT to the CAMSHAFT on many OHC engines. TIRES I hope you know what these are! TOP DEAD CENTER (TDC) A term used to define the point at which the PISTON as reached the very top of the STROKE. TORQUE CONVERTER A component of the DRIVE TRAIN. Transfers power from the engine to the transmission of automobiles with AUTOMATIC TRANSMISSIONS. Contains a set of rotors and transmission fluid. TORSION BAR A rod in the SUSPENSION system that, when twisted from one end, functions like a spring. TRANSAXLE A component consisting of a TRANSMISSION and DIFFERENTIAL drive gears assembled in the same case. Used on front-wheel drive automobiles. TRANSMISSION Part of the DRIVE TRAIN. The gear-changing or gear-shifting system through which engine power is transferred to the wheels. The purpose of gear-changing is to keep maximum engine power applied to the wheels at all times for all conditions, from start-up to high speeds. TURBOCHARGER A supercharging device driven by EXHAUST gases from the engine. TURNING (BRAKE DRUMS or ROTORS) A process used to recondition brake DRUMS or ROTORS. TWO-STROKE CYCLE An internal-combustion engine that requires one revolutions per CYLINDER or two PISTON strokes to achieve a power stroke: intake/compression stroke and power/exhaust stroke. Not as efficient as four-stroke-cycle engine. Used in many off-road recreational vehicles and boats. U V VACUUM Created when the PISTONS of the engine move down in the CYLINDER and pull in the air-fuel mixture. VALVE A component of the VALVE TRAIN. Opens and closes the COMBUSTION CHAMBER of an internal-combustion engine to admit the AIR-FUEL MIXTURE or EXHAUST the gases. Most engines have one or more valve for intake and exhaust for each cylinder. For example, a 32 valve V-6 engine has 2 intake and 2 exhaust valves for each of the 6 cylinders. VALVE GUIDE A component of the VALVE TRAIN. Usually located in the CYLINDER HEAD. Acts as a BEARING to guide the valve as it moves up and down. VALVE RETAINERS A component of the VALVE TRAIN. Used to prevent to VALVES from falling in the COMBUSTION CHAMBER. VALVE STEM The portion of a VALVE that the ROCKER ARM pushes on and rides in the VALVE GUIDES. VALVE TRAIN A collection of all the components that control the air intake and exhaust from the COMBUSTION CHAMBER. W WATER PUMP A component of the COOLING SYSTEM. Used to pump COOLANT through the engine and RADIATOR. Usually driven by the BELT DRIVE. WHEELS A term referring to the TIRES and RIMS. WHEELBASE The distance between the centers of the front and rear AXLES as viewed from the side of the car. X Y Z