Adjustable shocks:
shock absorbers(dampers) whose jounce and rebound characteristics can be stiffened or softened to compensate for wear or to fine-tune a suspension for a particular application such as rough roads, heavy loads or racing.

Aircooled engine:
an engine cooled by passage of air around the cylinders, not by passage of a liquid through internal water jackets.

Air-fuel ratio:
the mass of air supplied to the engine divided by the mass of fuel supplied in the same period of time. The Stoichipmetric, or chemically correct, air-fuel ratio (A/F ratio) is the exact ratio necessary to burn all the carbon and hydrogen in the fuel to carbon dioxide and water with no oxygen remaining. The fuel-air ratio is the reciprocal of the air-fuel ratio.

Air injection:
a system that injects air into the exhaust ports of a thermal reactor, for additional conversion of carbon monoxide to carbon dioxide and combustion of unburned hydrocarbons in the exhaust gases.

Air pump:
the device that supplies the fresh air needed by the air-injection system.

Automatic transmission:
A mechanism in the drivetrain with gearsets to vary the power and torque delivered to the driven wheels as a function of engine load and speed, usually incorporating a fluid coupling or torque converter to allow changing gears and reversing direction without using a foot operated clutch.

Belt:
a reinforcing band normally textile, fiberglass or steel, running around the circumference of a tire and strengthening the tread area.

Belted piston:
a piston with a continuous steel band cast into the skirt below the rings for controlling skirt expansion.

Blowoff valve:
a one-way valve that opens to the atmosphere above a certain set pressure to relieve excessive internal pressure buildup; often used with a turbocharger installation to the limit boost pressure to the engine.

Bore:
in a piston engine, the diameter of the cylinder, usually measured in either inches or millimeters.

Brake master cylinder:
a cylinder containing a movable piston actuated by hydraulic pressure to push fluid through the lines and wheel cylinders and force the brake lining or pads against a drum or disc.

Brake lines:
the tubes or hoses connecting the master cylinder to the wheel cylinders in a hydraulic brake system.

Brake pads:
for disc brakes, the replaceable flat segments consisting of a rigid backing plate plus frictional lining that take the place of the shoe and lining in a drum brake. Brake pads are sometimes referred to as brake pucks.

Brake Shoe:
the arc-shaped carrier to which the friction lining are mounted and which force the lining against the rotating drum during braking.

Breaker arm:
the movable part of a set of contact points in a distributor.

Bypass filter:
a type of filter in which only some of the oil from the oil pump flows through the filter, the remainder bypassing the filter in its way to various engine parts.

Caliper:
that part of a disc-brake assembly hat straddles the discs and contains the cylinders, pistons and brake pads. When the brakes are applied, brake fluid flows to the cylinders in the caliper and pushes the pistons out, forcing the pads against the disc. Also, an adjustable measuring tool for determining the diameter of a shaft, cylinder bore, etc. by contact and retaining the dimension for measurement or comparison.

Cam:
a rotating or sliding mechanism or a projection on a rotating shaft for imparting or receiving exact movements. A cam on a camshaft is also referred to as a lobe.

Camber:
inward or outward tilting of the wheels from vertical as viewed from the front or rear of the car. If the wheels are closer together at the top than at the ground, the chamber is negative; if the wheels are further apart at the top, the chamber is positive.

Chamber thrust:
side force generated when a tire rolls with camber. Camber thrust can add to or subtract from the side force a tire generates.

Carburetor:
a device through which air is drawn into the engine and mixed with fuel to form a combustible mixture that can be burned in the engine's cylinders. The carburetor changes the ratio of fuel and air according to varying engine operating conditions such as starting, idling, cruising and maximum power.

Caster:
the angle between the steering axis and the vertical, as viewed from the side. It is considered positive when the steering axis is inclined rearward at top.

Clutch:
a friction-operated device used to connect a driving to a driven member. In an automotive drivetrain the clutch, when engaged, connects the engine crankshaft and flywheel to the gearbox and thus the remainder of the drivetrain. It allows smooth coupling and uncoupling of the engine and drivetrain by slipping as its driving and driven discs come together.

Clutch disc:
the rotating circular metal plate splined to the transmission input shaft: it has friction material on each face. The disc is located between the flywheel and the clutch pressure plate and is clamped tightly between these two members when the clutch is engaged, thus transmitting power from the flywheel through the clutch and into the gearbox.

Coefficient of friction:
the ration of the frictional force between two surfaces to the perpendicular loading at their junction. The coefficient of friction depends primarily on the nature of both surfaces in contact, being relatively large if the surfaces are rough and small if they are smooth.

Combustion chamber:
the space at the top of the cylinder, in the head and/or piston top, remaining above the piston when it is at top dead center. Combustion of the fuel-air mixture begins here.

Compression ignition:
combustion of a fuel-air mixture without spark. In the diesel engine (after Rudolf Diesel, the inventor) air is drawn into the cylinder and compressed to a temperature sufficiently high that fuel oil injected at the end of the compression stroke burns in the cylinder without a spark to initiate combustion.

Compression ratio:
the extent to which the combustible gases are compressed within the cylinder: the ratio of cylinder and chamber volume with the piston at bottom dead center to the volume of the combustion chamber at the end of the compression stroke.

Compression ring:
a piston ring at the top of the piston, forming a seal with the cylinder wall to prevent compression loss or gas blowby. Compression rings also help transfer heat from the piston into the cylinder walls and thus to the water jacket surrounding the cylinder.

Compression stroke:
second stroke of the four-stroke cycle, in which the piston moves upward from bottom dead center, compressing the fuel-air mixture.

Compressor:
the mechanism in a refrigerator or air conditioner that pumps vaporized refrigerant out of the evaporator, compresses it to a relatively high pressure and then delivers it to the condenser.

Condenser:
a device for changing vapor into liquid, as in an air conditioning system. Applied to an electric circuit, a device (also called a capacitor) for temporarily collecting and storing a surge of electrical current for later discharge. In a car's ignition system the condenser is connected across the contact points to reduce arcing by providing a storage place for electricity as the points open.

Connecting rod:
the link between the piston and the crankshaft, by which the reciprocal motion of the piston is changed to rotary motion.

Constant-mesh gearbox:
a type of transmission in which all or most of the gears ate always in mesh with one another as opposed to a sliding-gear transmission, in which engagement is obtained by sliding some of the gears along a shaft into mesh.

Coolant:
the mixture of water and antifreeze that picks up heat from the engine and transfers it to the air passing through the radiator.

Countershaft:
that shaft in a manual gearbox that carries power by means of gears from the clutch shaft to the driveshaft, turning opposite to them.

Counterweight or counterbalance:
weight added to a rotating shaft or wheel to balance normal loads on the part and offset vibration. Counterweights are used on the crankshaft and are often found on the flywheel and driveshaft.

Cowl:
the portion of a car's body between the engine compartment and the driver which ordinarily houses the instruments and the plenum chamber for the heater-ventilation system.

Crankcase:
a box or case that encloses or encases the crankshaft.

Crankpin:
the bearing surface on a crank of the crankshaft to which the connecting rod is attached.

Crankshaft:
the main shaft of an engine, so named because of the U-shaped cranks. It delivers rotary motion taken from the reciprocating pistons and rods.

Cylinder:
the hollow tubular structure in the cylinder block in which the piston travels and combustion takes place.

Cylinder block:
the basic framework of the engine to which other engine parts are attached. It is usually a casting and includes the engine cylinders and the upper part of the crankcase.

Cylinder head:
a detachable part of the engine that attaches to the cylinder block, seals the cylinders and contains all or a portion of the combustion chamber. It has water and oil passages for cooling and lubrication; it holds the spark plugs and the valves.

Differential:
a gear system that transfers power from the driveshaft (or the transmission in a front-wheel-drive car) to the driving axles. It permits the outer driving wheel to turn faster than the inner when the car goes around a corner, to prevent skidding and tire scuffing.

Distributor:
a component of the ignition system containing the breaker points and cam, centrifugal advance and vacuum-advance mechanisms and a shaft usually driven be the camshaft. The high voltage generated by the coil passes into the center terminal of the cap mounted on top of the distributor housing. From there, it passes down the rotor, and as the rotor turns it distributes the current to terminals connected by high-tension wires to the sparkplugs.

Drag coefficient:
a dimensionless number used in calculating the aerodynamic drag acting on a car. The drag coefficient is a function of such factors as the shape of a car and airflow through the car for cooling or ventilation.

Driveshaft:
the long, hollow tube with universal joints at both ends that carries power from the transmission to the differential.

Drivetrain:
the power transmitting components in a car, including clutch and gearbox (or automatic transmission) driveshaft, universal joints, differential, and axle shafts.

Electronic ignition:
an ignition system using electronic switching devices to relieve the mechanical breaker points of part of their duties, or replace them.

Exhaust emissions controls:
systems or adjustments designed to limit noxious gases in an engine's exhaust. Such controls can be grouped into two broad categories: those designed to reduce or eliminate the formation of harmful pollutants in the engine itself (retarded spark settings are one example) and those designed to destroy or otherwise alter the pollutants after they have been formed.

Exhaust emissions:
unburned hydrocarbons, carbon monoxide, oxides of nitrogen and other noxious gases emitted when gasoline is burned in an engine.

Exhaust manifold:
an assembly of tubes that attaches to the cylinder head and provides a series of passages through which burned gases from the engine cylinders can flow to the exhaust system.

Exhaust stroke:
the fourth stroke of a four-cylinder cycle, in which the piston moves upward from bottom dead center to top dead center, pushing the burned exhaust gases out of the cylinder.

Exhaust system:
the pipes, resonators and mufflers that carry the exhaust gases from the exhaust manifold out into the atmosphere.

Exhaust valve:
a camshaft-driven valve in the cylinder head that opens to allow burned gases out of the cylinder and closes to form part of the combustion chamber during the compression and power strokes.

Expansion plug:
a steel plug, slightly dished or cup-shaped. When driven into place it flattens to fit tightly in its seat. In an engine block, expansion plugs (also called freeze plugs or core-hole plugs) are inserted into the holes in the casting through which core was removed when casting was formed. They open into cooling passages and thus provide pressure relief should the engine coolant freeze and expand.

Expansion tank:
a separate tank, partly filled with coolant, that connects to the radiator cap in a sealed cooling system,s. As the coolant in the engine is heated it expands and a portion is sent into the expansion tank. Then when the engine approaches operating temperature, a valve in the radiator cap closes, sealing the cooling system, and the valve opens, allowing coolant in the expansion tank or reservoir to flow back into the radiator. This keeps the cooling system filled at all times.

Expansion valve:
a part of an air-conditioning system, located between the condenser and the evaporator, that regulates the flow of liquid refrigerant to the evaporator.

External-combustion engine:
an engine that burns its fuel outside the engine. Steam engines are external combustion engines.

Filter:
a devise to remove suspended impurities or particles of foreign matter from the air intake, fuel, or lubricating system.

Floor shift:
a type of transmission shift linkage in which the various gears are actuated by a lever attached to the floor rather than by a lever attached to the steering system.

Flow-through ventilation:
a type of fresh air system in which outside air is ducted into the interior of the car, circulates through the passenger compartment and exits through openings in the C-pillars or rear-quarter panels.

Flywheel:
a heavy , toothed wheel mounted to the rear of the crankshaft that smooths out the separate power surges imparted to the crankshaft as each cylinder fires by resisting the tendency of the engine to speed up at the start of the power stroke and to slow down toward the end. It also serves as part of the clutch by transmitting power to the gearbox in a car with manual transmission, acts as a vibration damper and balance member for the crankshaft, and engages the teeth of the starter motor when the engine is cranked.

Foot-pound:
a measurement of work or energy. One foot-pound (ft-lb) is equal to the work done when a constant force of one pound is exerted on a body which moves a distance of one foot in the direction of the force.

Frame:
the structural load-carrying members of a car that supports the engine and body and are in turn supported by the car wheels.

Front-wheel drive:
a drive system in which the transmission is connected by driving axles to the front wheels instead of the rear wheels.

Fuel filter:
a device installed in the fuel line that prevents impurities in the fuel from reaching and possibly clogging the carburetor.

Fuel injection:
a type of fuel system using a pump and injectors instead of a carburetor to meter fuel.

Fuel line:
the pipe or tube through which fuel travels from the tank to the pump and from the pump through the carburetor or injector.

Fuel pump:
a mechanical or electrical device that draws gasoline from the fuel tank and delivers it to the carburetor or injector pump.

Fuel system:
the system that delivers fuel to the engine. It consists of a fuel tank, fuel filter, fuel pump, and the carburetor or fuel injector.

Full-floating axle:
drive axle construction where the axle shaft does not carry any car weight; its sole duty is to propel the car.

Full-flow filter:
the type of oil filter in which all the oil from the oil pump flows through the filter.

Gap:
generally refers to the distance the spark must travel in jumping from the center electrode in a sparkplug; or the spacing between the points in the contact breaker fitted to the distributor.

Gauge:
an instrument that registers the quantity of a substance such as fuel gauge.

Gearbox:
a device in the drivetrain consisting of an input shaft, a system of gears and an output shaft that multiplies engine torque.

Gear ratio:
the number of revolutions made by a driving gear compared to the number of revolutions made by the driven gear.

Gears:
wheel-like parts with teeth cut into the rim. Meshing of the teeth of two gears enables one to drive the other, thus transmitting power.

Gearshift:
the mechanism that allows the driver to move the transmission gears into various drive positions.

Heat-control valve:
a thermostatically operated valve in the exhaust manifold that allows some of the exhaust gases to pass around the intake manifold when the engine is cold to preheat the fuel mixture going to the cylinders.

Heated intake:
an antipollution device to help vaporize the gasoline supplied to a cold engine.

Heat exchanger:
a device that transfers heat between two fluids through a separating wall. A radiator is a type of heat exchanger that transfers heat from the liquid coolant to the atmosphere.

Heat range:
the ability of a sparkplug to transfer heat from the combustion chamber to the cylinder head.

Heel and toe:
a driving technique where the driver places the left side or the toes of his right foot on the brake pedal and the right side or the heels of his right foot on the throttle pedal so that he can simultaneously brake and throttle for a downshift. This is done to lessen the strain on the gearbox and drivetrain and makes for smoother driving.

Hydraulic:
any operation that uses the incompressibility of liquids, usually oil or water, and their ability to offer resistance when being forced into a small cylinder, thus transmitting an increase in applied force. Hydraulic brakes and clutches work on this principle.

Hydraulic valve lifter:
a lifter that by means of hydraulic oil pressure maintains zero valve clearance (no clearance between metal parts) so that valve noise is reduced.

Inboard brakes:
a type of brake design where the discs or drums and associated brake components are not located within the wheels.

Induction system:
the system that delivers the air-fuel mixture to the cylinders. Includes the carburetor or fuel-injection system, intake manifold, intake ports, and intake valves.

Intake stroke:
the first stroke of the four-stroke cycle during which the piston moves downward from top dead center to bottom dead center creating a partial vacuum and sucking the fuel-air mixture into the cylinder.

Intake valve:
a camshaft-driven valve in the cylinder head that opens to allow the fuel-air charge into the cylinder and closes to form part of the combustion chamber during the compression and power strokes.

Internal combustion engine:
one that burns its fuel withing cylinders or some other enclosed space.

Jump start:
cranking the engine of a car with a discharged or weak battery by attaching cables from the weak battery to a charged or helper battery.

Lateral acceleration:
sideways acceleration created when a car corners. As a result of this lateral acceleration, centrifugal force acts on the car and tried to pull it outward. To counteract this outward force the tires develop an equal and opposite force acting against the road.

Leading arm:
independent suspension system having the wheel attached to the end of an arm that swings in a plane parallel to the longitudinal axis of the car. The wheel is ahead of or leads the fixed pivot point of the arm.

Limited-slip differential:
one using cone or disc clutches to lock the two independent axle shafts together forcing both wheels to transmit their respective drive torque regardless of the traction available.

Lug nut:
the nuts used to secure the wheels to the car.

Master cylinder:
a cylinder containing a moveable piston actuated by foot pressure producing hydraulic pressure to push fluid through the lines and wheel cylinders and force the brake linings or pads against the drum or disc.

Motor:
principally a machine that converts electrical energy into mechanical energy.

Muffler:
a chamber attached to the exhaust pipe in which the exhaust gases expand and cool. It is usually fitted with baffles or porous plates that reduce or muffle the noise created by the exhaust.

Oil pan:
a removable part of the engine, usually made of pressed steel, that attaches to the bottom of a cylinder and acts as an oil reservoir.

Oil pump:
an engine-driven pump that delivers oil to all the moving engine parts.

O-ring:
a type of sealing ring usually of rubber or similar flexible material, that is compressed into grooves to provide the sealing action.

Overdrive:
generally a small auxiliary gearbox, usually mounted behind the car's main gearbox or attached to the differential, giving another gear in addition to the other three or four speeds in the main transmission.

Overhead cam or ohc:
a camshaft located above the cylinder head or heads instead of in the cylinder block.

Petroleum:
a complex mixture of hydrocarbons and small amounts of various other elements occurring widely in nature as deposits of decomposed organic matter.

Power steering:
a steering system generally using hydraulic pressure to multiply the driver's effort as he turns the steering wheel so that steering effort is reduced.

Push rod:
a connecting link in an operating mechanism, specifically the rod interposed between the valve lifter and the rocker arm on overhead-valve engines.

Rack-and-pinion steering:
steering system having a pinion gear on the end of the steering shaft that mates with a rack. When the steering wheel is turned, the pinion turns, moving the rack to the left or right. This movement is carried through tie rods to the steering arms at the wheels.

Refrigerant:
the substance used in an air-conditioning system that absorbs and gives up heat as it changes from a liquid to a gas to a liquid.

Rocker arm:
a lever located on a fulcrum or shaft, one end on the valve stem and the other either on the push rod or directly on the camshaft lobes. As the camshaft rotates, the arms rock on their fulcrums causing the valves to open and close.

Semi-elliptic springs:
type of leaf spring that takes its name from the shape which is part of an ellipse.

Semi-floating axle:
drive axle construction where the axle shaft supports the weight of the car in addition to being the means of propulsion.

Slick:
a treadless tire used for racing on dry surfaces.

Slip joint:
a variable length connection that permits the dive shaft or axle shaft to change its length as the shaft moves up and down.

Space frame:
type of frame construction offering high rigidity for minimum weight, used for some racing and low production cars.

Sparkplug:
a device inserted into the combustion chamber of an engine that provides the gap across which the high tension voltage jumps, creating a spark that ignites the compressed fuel-air mixture.

Speedometer:
an instrument for measuring and indicating the speed at which a car is traveling.

Stroke:
the distance the piston moves from bottom dead center to top dead center or vice-versa.

Suspension:
refers to the various springs, shock absorbers and linkages used to suspend a car's frame, body, engine and drivetrain above the wheels.

Thermal reactor:
a high-volume thermally isolated chamber replacing the exhaust manifold and providing a place for high-temperature afterburning of exhaust pollutants.

Thrust bearing:
a bearing with flanges on its two sides that prevents a shaft such as the crankshaft from moving endwise.

Tie rod:
in the steering system, the rods that link the pitman arm and the idler arm to the steering knuckle arms.

Timing:
refers to the crankshaft angles at which the valves and ignition points open and close.

Timing chain:
a chain for driving the camshaft from the crankshaft.

Timing gears:
a method of driving the camshaft from the crankshaft often used where long life and hard service are expected as in commercial vehicles and race cars.

Torsion bar:
a long straight bar fastened to the frame at one end and to a suspension part at the other.

Twincam:
an engine with double overhead camshafts.

Viscosity:
refers to the ability of a liquid to flow. An oil with high viscosity is very thick and flows slowly; an oil with low viscosity flows easily.

Water pump:
a pump normally mounted at the front of the engine and driven by a pulley and a belt from a pulley on the front end of the crankshaft. The pump has a number of curved blades that force the coolant to flow through the cooling system.

Watt linkage:
a three-bar linkage sometimes used for transverse location of a live axle.

Wheelbase:
the longitudinal distance from the center of the front wheel to the center of the rear wheel on the same side of the car.