Air/Fuel Ratio

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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 circuit. Ammeters are always connected in series with the circuit 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 (101 kPa at 0 degrees C).

Atomization - The breaking 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 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.

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 friction reducing, supportive device usually located a stationary part and a moving part.

Bimetal Temperature Sensor - Any sensor or switch made of two dissimilar types of metal that bend when heated or cooled due to the diferent 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 is; 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 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.

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 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 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.

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 over-loaded 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 prevent 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 refrigerant gas condenses into a liquid, giving off heat.

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

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

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