Glossary

Air/Fuel Ratio - The ratio of air-to-gasoline by weight in the fuel mixture drawn into the engine.

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.

Alternator - A device used for converting mechanical energy into electrical energy.

Ammeter - An instrument, calibrated in amperes, used to measure the flow of an electrical current in a cicuit. Ammeters are always connected in series with the cicuit being tested.

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.

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.

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 degrees F.

Atomization - The breking down of a liquid into a fine mist that can be suspended in air.

Axial Play - Movement parallel to a shaft or bearing bore.

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 insulato 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.

Ballast Resistor - A resistor in the primary ignition circuit that lowers voltage after the engine is started to reduce wear on ignition components.

Bearing - A fricton reducing, supportive device usually located between a stationary part and a moving part.

Bimetal Temp. Sensor - Any sensor or switch made of two dissimilar types of metal that bend when heated of cooled due to the differnent expansion rates of the alloys. These types of sensors usually function as an on/off switch.

Blowby - 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.

Brake Pad - A brake shoe and lining assembly used with disc brakes.

Brake Shoe - The backing for the brake lining. The term however, usually applied to the assembly of the brake backing and lining.

Bushing - A liner, usually removable, for a bearing; an anti-friction liner used in place of a bearing.

Caliper - A hydraulically activated device in a disc brake system, which is mounted stradling 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.

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.

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 the fuel in the proper proportion to allow even combustion.

Catalytic Converter - A device installed in the exhaust system, like a muffler, that converts harmful byproducts of conbustion into carbon dioxide and water vapor by means of a heat-producing chemical reation.

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.

Check Valve - Any one-way valve installed to permit the flow of air, fuel, or vacuum in one direction only.

Choke - A device, usually a moveable valve, placed in the intake path of a carburetor to restrict the flow of air.

Circuit - Any unbroken path through which an electrical current can flow. Also used to describe fuel flow in some instances.

Circuit Breaker - A switch which protects an electrical circuit from overload by opening the circuit when the current flow exceeds a predetermined level. Some circuit breakers must be reset manually, while most reset automatically.

Coil (ignition) - A transformer in the ignition circuit which steps up the voltage provided to 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 provent a vapor lock situation.

Compression Ratio - The comparison of the total volume of the cylinder and combustion chamber with the piston at BDC and the piston at TDC.

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 refridgerant gas condenses into a liquid, giving off heat.

Conductor - Any material through which an electrical current can be transmitted easily.

Continuity - Continuous or complete circuit. Can be checked with an ohmmeter.

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 - The main driving shaft of an engine which receives reciprocating motion from the pistons and converts it to rotary motion.

Cylinder - In an engine, the round hole in the engine block in which the piston(s) ride.

Cylinder Block - The main structural member of an engine in which is found the cylinders, crankshaft, and other principal parts.

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 the overhead valve engines, it contains the valves and their operating parts. On overhead cam engines, it contains the camshaft as well.

Dead Center - The extreme top or bottom of the piston stroke.

Detonation - An unwanted explosion of the air/fuel mixture in the combustion chamber caused by excess heat and compressio, advanced timing, or an overly lean mixture. Also referred to as "ping".

Diaphragm - A thin, flexible wall separating two cavities, such as in a vacuum advance unit.

Dieseling - A condition in which hot spots in the combustion chamber cause the engine to run on after the key is turned off.

Differential - A geared assembly which allows the tranmission of motion between drive axles, giving one axle the ability to turn faster than the other.

Diode - An electrical device that will allow current to flow in one direction only.

Disc Brake - A hydraulic braking assembly consisting of a brake disc, or rotor, mounted on an axle, and a caliper assembly containing, usually two brake pads which are activated by hydraulic pressure. The pads are forced against the sides of the disc, creating friction which slows the vehicle.

Distributor - A mechanically driven device on an engine which is responsible for electrically firing the spark plug at a predetermined point of the piston stroke.

Dowel Pin - A pin, inserted in mating holes in two different parts allowing those parts to maintain a fixed relationship.

Drum Brake - A braking system which consists of two brake shoes and one or two wheel cylinder, mounted on a fixed backing plate, and a brake drum, mounted on an axle, which revolves around the assembly.

Dwell - The rate, measured in degrees of shaft rotation, at which an electrical circuit cycles on and off.

Electronic Control Unit (ECU) - Ignition module, module, amplifier or igniter. See module for definition.

Electronic Ignition - A system in which the timing and the firing of the spark plugs is controlled by the electronic control unit, usually called a module. These systems have no points or condenser.

End-Play - The measured amount of axial movement in a shaft.

Engine - A device that converts heat into mechanical energy.

Exhaust Manifold - A set of cast passages of pipes which conduct exhaust gases from the engine.

Feeler Gauge - A blade, usually metal, of precisely predetermined thickness, used to measure the clearance between two parts.

Firing Order - The order in which combustion occurs in the cylinders of an engine. Also the order in which spark is distributed to the plugs by the distributor.

Flooding - The presence of too much fuel in the intake manifold and combustion chamber which prevents the air/fuel mixture from firing, thereby causing a no-start situation.

Flywheel - A disc shaped part bolted to the rear end of the crankshaft. Around the outer perimeter is affixed the ring gear. The starter drive engages the ring gear, turning the flywheel, which rotates the crankshaft, imparting the initial starting motion of the engine.

Foot Pound (ft. lbs. or sometimes, ft.lb.) - The amount of energy or work needed to raise an item weighing one pound, a distance of one foot.

Fuse - A protective device in a circuit which prevents circuit overload by breaking the circuit when a specific amperage is present. The device is constructed around a strip or wire of a lower amperage rating than the circuit it is designed to protect.When an amperage higher than that stamped on the fuse is present in the circuit, the strip or wire melts, opening the circuit.

Gear Ratio - The ratio between the number of teeth on meshing gears.

Generator - A device which converts mechanical energy into electrical energy.

Heat Range - The measure of a spark plug's ability to dissipate heat from its firing end. The higher the heat range, the hotter the plug fires.

Hub - The center part of a wheel or gear.

Hydrocarbon (HC) - Any chemical compound made up of hydrogen and carbon. A major pollutant formed by the engine as a byproduct of combustion.

Hydrometer - An instrument used to measure the specific gravity of a solution.

Inch Pound (inch lbs.; sometimes in.lb. or in.lbs.) - One twelfth of a foot pound.

Induction - A means of transferring electrical energy in the form of a magnetic field. Principle esed in the ignition coil to increase voltage.

Injector - A device which receives metered fuel under relatively low pressure and is activated to inject the fuel into the engine under relatively high pressure at a predetermined time.

Input Shaft - The shaft to which torque is applie, usually carrying the driving gear or gears.

Intake Manifold - A casting of passages or pipes used to conduct air or fuel/air mixture to the cylinders.

Journal - The Bearing surface within which a shaft operates.

Key - A small block usually fitted in a notch between a shaft and a hub to prevent slippage of the two parts.

Manifold - A casting of passages or set of pipes which connect the cylinders to an inlet or outlet source.

Manifold Vacuum - Low pressure in an engine intake manifold formed just below the throttle plates. Manifold vacuum is highest at idle and drops under acceleration.

Master Cylinder - The primary fluid pressurizing device in a hydraulic system. In automotive use, it is found in brake and hydraulic clutch systems and is pedal activated, either directly or, in a power brake system, through the power booster.

Module - Electronic control unit, amplifier or igniter of solid state or integrated design which controls the current flow in the ignition primary circuit based on input from the pick-up coil. When the module opens the primary circuit, high secondary voltage is induced in the coil.

Needle Bearing - A bearing which consists of a number (usually a large number) of long, thin rollers.

OHM - (Ω) The unit used to measure the resistance of conductor-to-electrical flow. One ohm is the amount of resistance that limits current flow to one ampere in a circuit with one volt of pressure.

Ohmmeter - An instrument used for measuring the resistance, in ohms, in an electrical circuit.

Output Shaft - The shaft which transmits torque from a device, such as a transmission.

Overdrive - A gear assembly which produces more shaft revolutions than transmitted to it.

Overhead Camshaft (OHC) - An engine configuration in which the camshaft is mounted on top of the cylinder head and operates the valve either directly or by means of rocker arms.

Overhead Valve (OHV) - An engine configuration in which all of the valves are located in the cylinder head and the camshaft is located in the cylinder block. The camshaft operates the valves via lifters and pushrods.

Oxides of Nitrogen (NOx) - Chemical compounds of nitrogen produced as a byproduct of combustion. They combine with hydrocarbons to produce smog.

Oxygen Sensor - Used with the feedback system to sense the presence of oxygen in the exhaust gas and signal the computer which can reference the voltage signal to an air/fuel ratio.

Pinion -