Automotive Definitions and Definitions for Auto Parts G-L
Definitions A-F	Definitions M-R	Definitions S-Z

Auto Parts Definitions

Gas Charged Shock Shock that contains low-pressure gas to keep the oil from foaming, and thus improve performance. These shocks are available for front and rear of your vehicle.  Gasket A wide variety of seals or packings used between matched machine parts or around pipe joints to prevent the escape of a gas or fluid..  Gasket Scraper A metal or plastic tool used to remove pieces of gasket and hardened oil or carbon deposits from engine parts.  Gas Line Freeze Results when moisture is in fuel turning to ice and blocking fuel line. Use of gasoline antifreeze usually prevents this occurrence. Gasohol A fuel consisting of a blend of ethyl alcohol and unleaded gasoline, especially a blend of 10 percent ethanol and 90 percent gasoline.  Gasoline Injection A modern gasoline injection system uses pressure from an electric fuel pump to spray fuel into the engine intake manifold.  Gas Turbine Engine that uses burning and expanding fuel vapor to spin fan-type blades  Hard Steering Greater than normal effort needed to turn steering wheel.  Hard to Shift A manual transmission problem often caused by damaged or sticking linkage.  Hard to Start Problem Usually caused by a partial system failure, such as a choke refusing to open.  Harmonic Vibration A high-frequency vibration caused by the crankshaft.  Harsh Shifts Transmission changes gears in a jerky manner.  HC Abbreviation for hydrocarbons (unburned fuel).  HC Readings The parts-per-million measuring of hydrocarbon emission.  Header Pipe Steel tubing connecting the exhaust manifold to the catalytic converter.  Head Gasket Markings Lines or words printed on gasket to indicate proper installation orientation.  Head Gasket Torque Sequence Tightening head bolts in specified sequence and in several stages of torque.  Headlamp System Components, such as battery, switches, fuses and lamps that make up the headlamp lighting circuit.  Headlight Aimer Device used to adjust headlights to specified positions.  Headlight Aiming Screen Set of measured lines on a wall, used to adjust headlight aim.  Heater Core A radiator-like unit that circulates heated engine coolant through a series of tubes. A fan blows air past the tubes to heat the passenger compartment of the vehicle.  Heater Hoses Flexible tubes that carry heated coolant between engine and the heater core.  Heating System Components that use engine cooling system heat to warm an automobile passenger compartment.  Heat Shields Metal plates that keep exhaust heat from transferring to other parts of the vehicle.  Heel The wide part of a gear tooth.  Height Sensor Lever-operated switch that reacts to changes in car-body height.  Height Sensor Link Rods that connect height sensor to suspension system.  Helical Gears Those with teeth cut at an angle to the centerline of the drive shaft.  Helicoil Spring steel insert used to repair damaged internal threads.  Hemi Chamber A dome-shaped (hemispherical) combustion chamber.  Hesitation Condition in which engine does not accelerate immediately when gas pedal is pressed.  High Side Section of an air conditioning system in which refrigerant is under high pressure.  Holding Tools Vises, clamps, and fixtures that grip a part while it is being worked on.  Honing Grit Fine bits of stone and metal remaining after a cylinder is honed. This material must be removed from the engine before it is reassembled, or it will cause severe wear.  Gear Backlash Small amount of clearance between meshing gear teeth.  Gearbox Overhaul Disassembly, cleaning, adjusting, and replacing parts as necessary.  Gearbox Ratio The relationship (number of turns) between the steering wheel and the sector gear.  Gear Clash A noise that is heard when gears fail to mesh properly in a manual transmission.  Gear Oil High viscosity oil (80W or 90W) used in transmissions.  Gear Pump Oil pump using meshing gears to provide pressure and oil movement.  Gear Ratio The number of rotations a driving gear must make while the driven gear is completing one revolution.  Gear Reduction The situation in which a small gear is used to drive a larger gear, with an increase in torque as a result.  General Repair Manual Service manual covering many makes and models of cars, usually over a several-year span.  Glow Plug A heating element that helps start a diesel in cold weather.  Glow Plug Resistance-Balance Test A diagnostic procedure used to determine whether all cylinders of a glow plug equipped diesel engine are firing.  Governor A device used to control an engine's speed.  Grabbing Brakes Abrupt, hard application of brakes when pedal is only lightly depressed.  Grade Markings Lines on bolt head, indicating tensile strength.  Grease Gun Tool used to inject lubricating grease, under pressure, into fittings.  Grease Job Process of forcing a thick lubricant, under pressure, into friction points on the chassis, steering system, and driveline.  Grease Rack Lift used to raise car for lubrication or other work.  Grease Seal Component that prevents lubricant leaking from axle assembly into steering knuckle or bearing support.  Gross HP Horsepower developed with only basic accessories in use.  Group Injection Operation of some (usually half) of the injectors simultaneously.  Growler Testing device used to check armatures for shorts.  Hall Effect A type of pickup used with many electronic ignition systems.  Halogen Headlamp One with a small, high-intensity halogen lamp inside a conventional scaled housing.  Hangers Rubber and metal fasteners that suspend the exhaust components from the underside of the vehicle.  Hard Failure One that is always present (not intermittent), such as a disconnected wire.  Horsepower Measure of an engine's ability to perform work.  Hotchkiss Drive Open drive shaft that operates a rear axle assembly mounted on springs. The most common rear-wheel drive type.  Hot Idle Compensator Component that prevents stalling when engine temperature is high.  Hot Plug One with a long insulator tip, often used in older engines.  Hot Tank Cleaning tank with heated chemicals in which parts are immersed.  Hub Mounting place for vehicle wheel on end of axle or spindle.  Hybrid A vehicle using two different methods of propulsion, such as a small gasoline engine and an electric motor with batteries.  Hydraulic Actuator Solenoid-operated valve and electric pump mechanism.  Hydraulic Booster Braking system booster actuated by hydraulic pressure from the power steering pump.  Hydraulic Circuit Diagrams A schematic showing how transmission parts and passages interconnect.  Hydraulic Head The housing around a diesel injection pump plunger.  Hydraulic Lifter Oil-filled lifter that maintains zero valve clearance.  Hydraulic Press Machine used to exert pressure on parts that are being forced (press-fit) together.  Hydraulic System Arrangement of pistons and tubing that uses pressure to transmit force from one part to another.  Hydrocarbon Chemical mixtures (12 percent hydrogen, 82 percent carbon) making up crude oil, or petroleum.  Hydrometer Tool used to test for specific gravity indicating the condition of a batteries electrolyte and its ability to charge/hold a charge.  Hypoid Gears Gear arrangement with the pinion centerline well below the centerline of the ring gear.  Idle Air Control Valve Solenoid operated valve in a Till system that regulates idle speed.  Idle Mixture Screw Adjusting device that meters fuel into the air horn.  Ignition Coil Device used to produce the high voltage needed for ignition spark.  Ignition Computer ECM that controls ignition timing, based on sensor input.  Ignition Distributor Component that directs coil voltage to each spark plug at the appropriate time.  Ignition Lag The time required for diesel fuel to vaporize, heat up, and begin to burn.  Ignition Spark Switch Used on some manual transmissions, this switch permits distributor vacuum advance in high gear.  Ignition System Components that produce a spark to ignite the air-fuel mixture in the engine.  Ignition Timing How early or late the spark plug fires in relation to the piston position.  L-Head One with intake and exhaust valves in the cylinder head.  IHP Indicated horsepower.  Impact Socket An attachment to an air-powered impact wrench.  Impeller Pump component with fan-like blades that spins inside a housing to move liquid.  Improper Injector Spray Pattern One that is restricted due to foreign matter in the injector.  In Board CV-Joint The inner universal joint on a front-wheel drive vehicle.  Incorrect Camber Condition that produces wear on one side of tire tread.  Incorrect Shift Points The transmission shifts too soon or too late in relation to engine speed.  Incorrect Toe Condition that produces a feathered edge on tire tread.  Independent Suspension System that permits each wheel to move up and down without seriously affecting any other wheel.  Inflation Pressure The amount of air pressure that a tire can safely handle.  Initial Ignition Timing Timing set with ignition idling.  Injection Pressure Tester A test device for precisely measuring diesel injection pressure.  Injection Pump A pump that meters fuel in a diesel system.  Injection Pump Test Stand Specialized testing equipment for use with injector pumps.  Injection Pump Timing Adjustment of the pump operation to match the engine's operating cycle.  Injection Timing The relationship between injection of fuel and the positions of the engines pistons.  Injector A spring-loaded valve that meters fuel into the pre-combustion chamber of a diesel engine.  Injector Leakage Dripping or spraying of fuel when the injector nozzle is closed.  Injector Opening Pressure Amount of pressure needed to open the injector nozzle.  Injector Output Volume The amount of fuel output over a specific time period.  Injector Rebuild A process involving cleaning, disassembly, replacement of worn parts, and the reassembly of a nozzle.  Injector Spray Pattern Shape of the spray produced by an injector.  Inlet Air Temperature Sensor The device that checks temperature of air entering the engine.  In-Line Engine One with cylinders lined up in a row.  In-Line Pump A diesel injection pump with one plunger (piston) for each cylinder.  Inner Stub Shaft Section of front-drive axle that is splined to differential gears. It is connected to the interconnecting shah through a universal joint.  Input The information provided to a computer by a sensor.  Input Shaft Metal shaft that transfers motion from the engine (via the clutch) to the transmission.  Instrumentation Computer One that uses sensor output to control dashboard displays.  Insulated Current Resistance Test Check of all parts between the battery positive and the starting motor for excess resistance.  Insulator A material that resists the flow of electrons.  Intake and Exhaust Ports Openings into the combustion chamber that are controlled by valves.  Intake Manifold Component that directs the air-fuel mixture from the carburetor or throttle body to the cylinders.  Intake Stroke Piston stroke that draws the air-fuel mixture into the cylinder.  Integral Power Steering A system in which the hydraulic piston is mounted inside the gearbox.  Integral Regulator A regulator that is mounted in or on an alternator.  Integral Valve Guide One machined into the cylinder head.  Integral Valve Seat One machined into the cylinder head.  Integrated Circuit A tiny "chip" of silicon containing complete electronic circuits.  Interconnecting Shaft Component of front-drive axle that connects inner and outer universal joints.  Interface Another name for a computer conditioner.  Interference Angle Slight difference in angle between valve face and valve seat for improved sealing when valve is closed.  Intermittent Problem One that occurs only under some conditions.  Internal Cam Ring A collar with lobes that operates diesel injectors.  Internal Oil Leakage Loss of oil by burning in the cylinders as a result of piston ring wear.  Jounce Bumper Rubber blocks that keep suspension parts from hitting the frame when the vehicle encounters large bumps or holes.  Journal Out-of-Roundness Greater wear on the top or bottom section of a crankshaft journal.  Journal Taper Difference in diameter of a crankshaft journal from one side to the other.  Jumper Cables Electrical cables used to start a car with a dead battery.  Jumper Wire A wire used to make a temporary electrical connections when testing electrical circuits.  Jumps Out of Gear A manual transmission problem in which the transmission will unexpectedly disengage and move into neutral.  Jump Starting Providing current to a car with a dead battery by connecting cables to the battery of an operating car.  KAM Keep-alive memory.  Key Metal piece that locks into a slot (keyway) to keep a part and a shaft turning together.  Kick-Down Valve Component that causes automatic transmission to shift down into a lower gear during fast acceleration.  Knock Engine noise caused by detonation.  Knock Sensor Engine sensor that detects detonation in the engine.  kV Kilovolt (1000 volts).  Lapping Valves A polishing operation with a fine grin ding compound that helps smooth the mating surfaces of valve faces and valve seats.  Lateral Run-Out Side-to-side movement of a wheel or tire.  Leaded Gasoline Fuel with an antiknock additive. Leaf spring Flat pieces of spring steel that are stacked and bound together. Normally used as part of a vehicle's rear suspension.  Leak Detector Device used to locate refrigerant leaks in a system.  Leaking Exhaust Manifold Gasket Creates metal-like rapping sound.  Leaking Heater Core Rusted or cracked tube in core, allowing coolant to escape.  Leaking Injector One that allows extra fuel to drip out, causing a richer mixture.  Leaking Intake Manifold Gasket Possible case of vacuum leak resulting in rough idle.  Leaking Valve Seal A condition that allows oil to be drawn into intake or exhaust port and burned causing blue smoke.  Lean Air-Fuel Ratio An air-fuel mixture that contains more air than a stoichiometric mixture.  Led Code Trouble code displayed as a pattern of lighted code.  L-Head One with both the intake arid exhaust valves ii~ the block.  Lift See Grease Rack.  Lifter Leak-Down Rate Time required for a hydraulic lifter plunger lobe pushed to the bottom of its stroke under cent roiled conditions.  Lifting Fixture or Chain Device fastened to an engine to allow it to be lifted by a crane or hoist.  Limited Slip Differential One that provides a driving force to both real wheels at all times.  Limited Slip Differential Chatter Sound made when turning a corner, caused by sticking and releasing of clutches in the differential.  Line Bore A machining operation resulting in a carefully aligned series of holes through an engine block for the crankshaft bearings.  Liner A thin rubber layer bonded to plies and forming the inside surface of the tire.  Line Wrench Special wrench with split jaw that can be slipped over tubing (such as a fuel line) to tighten or loosen compression fittings.  Liquid-Vapor Separator Tank that permits liquid fuel to settle out and flow back to fuel tank.  Liquid Cooling System Circulation of a heat-absorbing medium through engine passages, with the accumulated heat dissipated by further circulation through heat exchanger (radiator).  Load or Acceleration Test Oscilloscope reading that measures the firing voltages of the spark plugs when the engine is accelerating rapidly.  Load Rating The maximum amount of weight a tire can carry when inflated to the recommended pressure.  Locked-in Gear A manual transmission problem often caused by damaged or sticking linkage. Broken gear teeth can also be at fault.  Locking Hub Components that transfer power from driving axles to driving wheels on a four-wheel-drive vehicle.  Lock-up Converter A variation of the fluid coupling, with an internal friction clutch mechanism. It 'locks up" in high gear, improving fuel economy.  Longitudinal Lengthwise; term used to identify an engine mounted with its centerline on or parallel to the centerline of the vehicle.  Low Brake Pedal Farther than normal brake pedal travel before braking begins.  Low Pressure Cutout Switch One that pre\ cuts compressor operation and possible damage if air conditioning system pressure drops below a set point.  Low Side Section of an air conditioning system in which refrigerant is under high pressure.  LPG Liquefied petroleum gas, an alternate fuel.  Lubrication Service The process of checking and adjusting the levels of all lubricants in a vehicle.  Lubrication System Method of distributing lubricant (oil) to moving parts to minimize friction.  Lug Nut Large steel nuts used to hold a wheel into the axle hub.  Lug Stud Special bolts that are press-fit into the axle hub and accept lug nuts to mount the vehicle's wheels.

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