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    GLOSSARY TERMS

    I

    I-4
    An abbreviation for an inline four-cylinder engine.
    I-Beam Axle
    A beam axle having an I-shaped cross section.
    I-Beam Rod
    A connecting rod having an I-shaped cross section.
    I-Head
    An overhead valve engine having both intake and exhaust valves directly over the piston.
    I-Head Engine
    An overhead valve engine with the valves in the head.
    I.D.
    An abbreviation for internal diameter or inside diameter.
    I/M
    An abbreviation for inspection maintenance.
    I/M 240
    A 240-second emissions-inspection program that uses loaded-mode testing that simulates the federal urban test cycle for certifying new vehicle-emissions performance.
    IC
    An abbreviation used for internal-combustion engine.
    ICE
    An acronym for internal-combustion engine.
    Ice-Melting Capacity
    A refrigeration effect equal to the latent heat of fusion of a stated weight of ice, at 144 Btu per pound.
    Ideal air/fuel ratio
    A term used for Stoichiometric air/fuel ratio.
    Ideal Humidity
    Most people are comfortable at a relative humidity of 45% to 50%.
    Ideal Temperature
    Most people are comfortable at a temperature from 68° to 72°F (20° to 22.2°C).
    IDI
    An abbreviation for indirect injection.
    Idiot Box
    An automatic transmission.
    Idiot Light
    The system-malfunction warning lights on a dashboard.
    Idiot Proof
    A product that is designed to be as simple as possible to operate.
    Idle
    The engine speed with no load and the accelerator pedal fully released.
    Idle Air-Control Valve
    A General Motors electrically operated valve that, on commands from the engine-control computer, varies the size of an air passage that bypasses the throttle plate of an electronic fuel-injection system, thus controlling idle speed.
    Idle Circuit
    The system within a carburetor that meters fuel when the engine is running at low rpm.
    Idle Compensator
    A term used for engine-idle compensator or hot-idle compensator.
    Idle Limiter
    A device that controls the maximum richness of the idle air/fuel mixture in the carburetor.
    Idle Mixture
    The air/fuel mixture supplied to the engine while idling.
    Idle Port
    An opening into the carburetor throttle body through which the idle system discharges fuel.
    Idle Speed
    The speed at which an engine idles in revolutions per minute (rpm), usually between 600 and 850 rpm. The idle speed is specified on the under-hood emissions decal.
    Idle System
    The passages of a carburetor through which fuel is fed when the engine is idling.
    Idle Vent
    An opening in an enclosed chamber through which air can pass under idle conditions.
    Idle-Limiter Cap
    A plastic device pressed over a carburetor's idle-mixture screw that limits the amount of adjustment during service to help eliminate excessive air pollution that is caused if the mixture is too rich.
    Idle-Mixture Adjusting Screw
    An adjustment screw on some carburetors that is turned in or out to lean or enrich the idle air/fuel mixture.
    Idle-Mixture Adjustment
    An adjustment made on carbureted engines by removing the antitampering plugs and turning the idle-mixture screws until the proper idle mixture is achieved. Setting the idle mixture on an emissions-controlled engine may require monitoring exhaust CO or using a special procedure called propane enrichment.
    Idle-Speed Adjusting Screw
    A screw on the carburetor used to adjust engine-idle speed.
    Idle-Speed Adjustment
    The idle speed on carbureted engines without computer idle-speed control is set by turning a screw that opens or closes the throttle plates. On fuel-injected engines without computer idle-speed control, idle speed is set by turning an idle-air bypass screw that allows air to bypass the throttle plates. Idle speed is not adjustable on engines with computer idle-speed control.
    Idle-Stop Solenoid
    An electromagnetic device mounted on the carburetor linkage that maintains the proper throttle opening for specified idle speed while the ignition is on, but allows the throttle to close further when the ignition is switched off, reducing the amount of air that can enter the engine and the likelihood of dieseling.
    Idler Arm
    A pivoting component that supports the right side of the steering relay rod in much the same manner as the pitman arm supports the left side.
    Idler Eccentric
    A device used in a belt-drive system using the idler pulley as a means of tightening the belt.
    Idler Gear
    A gear connecting two other gears in a manner so that they will turn in the same direction.
    Idler Pulley
    A pulley that is used to adjust the belt in a belt-drive system.
    If you can't find 'em, grind 'em
    An admonition to a driver who misses a shift.
    IFS
    An abbreviation for independent front suspension.
    Ignition
    The firing of a spark plug to ignite the air/fuel mixture in the combustion chamber.
    Ignition Advance
    The moving forward, in time, of the ignition spark relative to the piston position.
    Ignition Coil
    A transformer containing a primary and secondary winding that acts to boost the battery voltage of 12 volts to as much as 30,000 volts to fire the spark plugs.
    Ignition Distributor
    A term used for distributor.
    Ignition Map
    A chart showing the precise advance and retard of the ignition on an electronic control-equipped engine.
    Ignition Points
    A term used for points.
    Ignition Reserve
    The difference between the minimum available and maximum required voltage for proper operation.
    Ignition Resistor
    A resistance element in series with the primary circuit to reduce the voltage supplied to the coil during engine operation.
    Ignition Retard
    The moving back in time of the ignition spark relative to the position of the piston.
    Ignition Switch
    A five-position switch that is the power distribution point for most of the vehicle's primary electrical systems. The spring-loaded START position provides momentary contact and automatically moves to the RUN position when the key is released. The other switch detent positions are ACCESSORIES, LOCK, and OFF.
    Ignition System
    The major components, such as the battery, coil, ignition switch, distributor, high-tension wiring, and spark plugs, that provide the right spark at the right time to ignite the air/fuel mixture.
    Ignition Temperature
    The lowest temperature at which a combustible material will ignite and continue to burn independent of the heat source.
    Ignition Timing
    The timing of the spark, expressed in crankshaft degrees, in relation to top dead center.
    Ignition Timing-Retard Sensor
    A term used for knock sensor.
    IHP
    An abbreviation for indicated horsepower.
    IHRA
    An abbreviation for the International Hot Rod Association.
    IKF
    An abbreviation for the International Karting Federation.
    IMACA
    An abbreviation for International Mobile Air Conditioning Association.
    IMCA
    An abbreviation for International Motor Contest Association.
    IMEP
    An abbreviation for indicated mean effective pressure.
    Impact Failure
    The failure of a part or assembly due to repeated impact or off-square seating.
    Impact Hardness
    The hardening of a part caused by repeated impacts.
    Impact Particle Cleaning
    A method of cleaning parts using air-propelled glass beads.
    Impeller
    A rotor that transmits motion such as a centrifugal pump, supercharger, turbine, or fluid coupling.
    IMS
    An abbreviation for the Indianapolis Motor Speedway.
    IMSA
    An abbreviation for the International Motor Sports Association.
    In and Out Box
    A racing transmission having a neutral and a single direct drive forward gear.
    In the Chute
    Staged for a drag race.
    In-Car Sensor
    A term used for in-car temperature sensor.
    In-Car Temperature Sensor
    A thermistor used in automatic temperature-control systems for sensing the in-car temperature.
    In-Duct Sensor
    A thermistor used in automatic temperature control units for sensing the in-duct return air temperature.
    In-H2O
    An abbreviation for inches of water column.
    In-Hg
    An abbreviation for inches of mercury.
    In-lb
    An English measure of torque.
    In-Line Engine
    An engine having all its cylinders in one line or row.
    In-Line Steering Gear
    A type of integral steering system.
    In-Phase
    The in-line relationship between the forward coupling-shaft yoke and the drive-shaft slip yoke of a two-piece drive line.
    In-Vehicle Sensor
    A term used for in-car sensor.
    In-Vehicle Temperature Sensor
    A term used for in-car sensor or in-car temperature sensor.
    Inactive Spring Coil
    Inactive coils located at the end of a spring introduce force into the spring when a wheel strikes a road irregularity.
    Inadequate Crush
    An insufficient crush on a pair of bearing shells allowing excessive clearance between the bearings and the shaft.
    Inadequate Joint Penetration
    Joint weld penetration that is sufficient to properly bond the base metals.
    Inboard
    Toward the centerline of the vehicle.
    Incandescence
    Glowing due to heat.
    Incandescent
    That which gives light or glows at a white heat.
    Incandescent Lamp
    An electric lamp or bulb containing a thin wire or filament of infusible conducting material.
    Inch-Pound
    An English measure of torque.
    Inches of Mercury (in-Hg)
    A term used to designate a vacuum on the English scale.
    Inches of Water Column (in-H2O)
    An engineering term used to designate pressure such as inches of mercury or kilo Pascals.
    Inclined Surface
    A slope or slanted surface.
    A valve rotator.
    Included Angle
    Sum of the kingpin or ball-joint inclination angle and the camber angle of a vehicle's front wheel.
    The sum of the camber angle added to the steering axis-inclination angle.
    The angle included between the outer surfaces of the link-plate contours of a silent chain that meshes with the sprocket tooth form.
    Incomplete Joint Penetration
    Joint penetration that is unintentionally less than the thickness of the weld joint.
    Independent Front Suspension (IFS)
    A suspension-system method of supporting the chassis on the wheels without the use of rigid axles where the movements of the two front wheels are not interdependent; one wheel does not force the other wheel to change its plane of rotation.
    Independent Publishers
    Publishers that provide service and repair information on a variety of subjects, such as automobiles. An example is this manual by Delmar Publishers.
    Independent Rear Suspension (IRS)
    A suspension system in which both rear wheels are free to move independently of the other, providing a reduction of unsprung weight as well as overall vehicle-weight reduction.
    An independent suspension system at the rear of the vehicle.
    Independent Service
    General or specialty service provided by independent garages on all types and makes of vehicles.
    Independent Suspension
    A suspension system by which a wheel on one side of a vehicle can move vertically without affecting the wheel on the other side, and wheel jounce or rebound travel of one wheel does not directly affect the movement of the opposite wheel.
    Index
    To examine and adjust rod journal spacing and alignment.
    The elapsed time assigned to various classes in drag racing used to calculate starting-time differences for handicap or bracket racing.
    Installing a camshaft relative to the crankshaft so the valves open and close at precisely the right time.
    Indianapolis Motor Speedway (IMS)
    A very popular race course, not in Indianapolis, but in Speedway, Indiana.
    Indianapolis Raceway Park (IRP)
    Better known as Indy. The site of the U.S. Nationals on Labor Day weekend.
    Indicated Horsepower (IHP)
    A measurement of power developed by the combustion processes in the cylinders, not considering friction.
    Indicated Mean Effective Pressure (IMEP)
    The average of the pressures developed in the cylinders during the four-stroke cycle, intake, combustion, exhaust, and compression.
    Indicated Speed
    The vehicle speed as indicated on a speedometer.
    Indicated Torque
    Torque as calculated from the indicated mean effective pressure, which is an actual indication of output developed within the cylinders.
    Indirect Injection (IDI)
    A system in which fuel is injected into a prechamber, where it is ignited before entering the main combustion chamber.
    Induction
    A synonym for intake.
    A process whereby an electromagnet or electrically charged object transmits magnetism or an electric current to a nearby object without making physical contact.
    Induction Coil
    An electrical device that receives low battery voltage in its primary winding and delivers pulsating high voltage in its secondary winding as the primary field is energized and collapsed by use of a set of points.
    Induction Hardening
    A process of hardening the surface of a part by placing electric coils next to it.
    Indy
    Short for Indianapolis Motor Speedway.
    Short for Indianapolis Raceway Park.
    Indy 500
    A race held every Labor Day weekend at Indianapolis Motor Speedway. It is an American classic, the single largest spectator-attended sporting event in the world.
    Indy Car
    An open-wheeled vehicle built especially for Indy and CART racing.
    Indy Lights
    A junior series of Indy racing sponsored by CART.
    Inert Gas
    A gas that normally does not combine chemically with materials.
    Inertia
    The property of a moving object that causes it to resist any change in speed or direction.
    Inertia Lock Retractor
    A passive seat-belt system that uses a pendulum mechanism to lock the belt tightly during a sudden change in movement.
    Inertia Weight
    A small, steel flywheel used to dampen drive-line vibrations on certain applications; generally located on the slip yoke, drive pinion yoke, or near an end of the drive shaft.
    Inertial Scavenging
    An exhaust system that uses the momentum of flowing gases to pull more gases through.
    Infield
    An area enclosed by an oval track or a road course.
    Inflation Pressure
    The amount of air pressure required to inflate a tire, measured in psi or kPa.
    Information Center
    The electronic display in some luxury vehicles that shows such data as the date, inside and outside temperature, trip distance traveled and distance remaining, time of departure and estimated time of arrival, average and current speed, average and instantaneous fuel economy, fuel used and remaining, and, often, an appointment reminder.
    Information Sheet
    A form that is used to record pertinent information about a vehicle.
    Infrared Exhaust Analyzer
    An instrument able to detect and measure hydrocarbons, carbon monoxide, carbon dioxide, and oxygen levels.
    Inhibitor
    A substance used to reduce the rate of a chemical or electrochemical reaction.
    Injected
    An engine equipped with a fuel injector.
    Injection Cylinder
    A term used for oil-injection cylinder.
    Injection Valve
    A term used for fuel injector.
    Injector
    The tube or nozzle through which fuel is injected into the intake airstream of the combustion chamber.
    A term used for fuel injector.
    Injector Body
    The housing for a fuel-injection system.
    Injector Fuel
    The fuel that is stored inside the injector prior to use.
    Injector Tube
    The copper or brass tube used in diesel cylinder heads to cool fuel injectors and seal combustion pressures.
    Inlet
    A synonym for intake.
    Innards
    The internal parts of an assembly.
    Inner Liner
    A synthetic, gum-rubber layer molded to the inner surface of a tire for sealing purposes.
    Inner Shaft
    A shaft upon which the inner end of the upper control arm pivots in a front suspension system.
    Inner Tube
    An inflatable rubber bladder mounted inside some tires to contain the air.
    Inner-cam Clutch
    A one-way roller clutch that has the cam profile surfaces on the inner element.
    Input Retarder
    A paddle-wheel-type unit located between the torque converter housing and the main housing in the retarder housing; primarily for over-the-road operations.
    Input Shaft
    The transmission shaft that receives power from the engine.
    Insert Valve Guides
    Replaceable valve guides.
    Insert Valve Seats
    Replaceable valve seats.
    Inside Diameter (i.d.)
    The diameter of the inner walls of a pipe or tube.
    Inside-Vehicle Lubrication Services
    Work performed inside the vehicle during a chassis lubrication such as changing the mileage sticker, lubricating the ignition-lock cylinder and the glove-compartment hinges and lock, and inspecting safety-related items.
    Inspect
    To examine a component or system for any audible or visual signs of a defect.
    Inspection
    The process of measuring, examining, testing, gauging, or otherwise comparing the unit with the applicable requirements or specifications.
    Inspection Maintenance (I/M)
    The periodic and systematic inspection and maintenance of a vehicle's ignition, fuel, and emissions-control systems.
    Install
    To set up an accessory part or kit for use in a vehicle.
    Installed Height
    The distance from the valve-spring end to the valve-spring seat.
    Instant Center
    An imaginary center point around which a wheel appears to pivot.
    Insulated return System
    The ground wire of a two-wire electrical system.
    Insulation
    Any material that blocks the flow of electricity.
    Insulation Tape
    Tape (usually cork) used to wrap refrigeration hoses and lines to prevent condensate drip.
    Insulator
    A material with high electrical resistance that supports or separates conductors to prevent undesired flow of current to other objects.
    Insulator Ribs
    In a spark plug, unevenly spaced circular ridges on the upper section of the insulator to reduce or prevent flashover of the high voltage from the terminal to the lower shell.
    Insurance Information Institute
    A public information and communications association.
    Insurance Institute for Highway Safety
    A highway and vehicle safety research organization.
    Intake
    The point at which a fluid or gas enters a pipe or channel Z. The act of taking in.
    Intake Manifold
    A metal component used to duct:
    The air/fuel mixture from the carburetor to the intake ports.
    Air in an injected engine to the intake ports.
    Intake Over Exhaust (IOE)
    An engine design having intake valves in the cylinder head and exhaust valves in the block.
    Intake Ports
    Passages in the cylinder head that direct air/fuel mixture from the intake manifold to the intake valves.
    Passages in an L-head engine block that direct the air/fuel mixture from the intake manifold to the intake valves.
    Passages in the head or block of an injected engine that direct air to the intake valves from the intake manifold.
    Intake Stroke
    A downward stroke of a piston that draws the air/fuel mixture into the cylinder.
    Intake Valve
    A valve that opens to admit the air/fuel mixture.
    Integral
    Internal or built-in as a part of the whole.
    Integral Valve Guide
    A valve guide machined into the cylinder head.
    Integral Valve Seat
    A valve seat machined into the cylinder head.
    Integral-Type Power Steering
    A steering system with a built-in power assist.
    Inter Industry Conference on Auto Collision Repair
    An international, collision-repair training organization.
    Inter-Axle Differential
    A third differential between the front and rear differentials that permits differences in speed between the front and rear driving axles.
    Inter-Changeability
    The basis of mass production; the production of parts that are consistent in size, tolerance, and specifications.
    Intercooler
    A radiator-like heat exchanger between the supercharger or turbocharger and the engine to cool the air/fuel mixture.
    Interface Fit
    A term used for interference fit.
    Interference Angle
    The difference between the valve face angle and the valve seat angle.
    Interference Fit
    A fit having limits of size, 0.0005 to 0.0007 inch (0.0127 to 0.0178 millimeters) so prescribed that an interference always results when mating parts are assembled by pressing them together. Also known as drive fit and interface fit.
    Interference Valve Angle
    The difference between the valve face angle and the valve seat angle, usually one or two degrees.
    Interior Lights
    The inside vehicle-lighting system, including courtesy, dome, map, and instrument-panel lights.
    Interlock
    An electrical-circuit arrangement that prevents a second operation from taking place until the first operation is completed.
    Intermediate Gear
    A small torque increase obtained from a planetary gear set when the sun gear is held and power is applied to the internal gear.
    Intermittent Duty
    A service requirement that demands electrical or mechanical operation for alternate intervals of load and no load; load and rest; or load, no load, and rest.
    Internal Gear
    A gear with teeth pointing inward toward the center of the orifice.
    Internal-Combustion Engine (IC)
    An engine that burns the air/fuel mixture in a chamber inside the engine cylinder, like a conventional reciprocating engine or a rotary engine.
    International Carwash Association/National Carwash Association
    A trade association consisting of carwash owners, operators, manufacturers, distributors, and suppliers.
    International Franchise Association
    A trade association representing franchisors, franchisees, suppliers, educational institutions, and franchise associations from other countries.
    International Hot Rod Association (IHRA)
    A drag-racing sanctioning body.
    International Karting Federation (IKF)
    A major kart-race sanctioning body.
    International Mobile Air Conditioning Association (IMACA)
    A trade association of manufacturers and distributors of automotive air conditioners and parts.
    International Motor Contest Association (IMCA)
    An automobile race-sanctioning body of drivers, owners, and mechanics created to establish rules, regulations, and specifications.
    International Motor Sports Association (IMSA)
    A road-racing sanctioning body.
    International Race of Champions (IROC)
    An annual series for top drivers from various forms of oval-track and road racing who are invited to compete, driving identical spec cars.
    International Show Car Association (ISCA)
    A promoter of International Championship Custom Car Shows.
    International Truck Parts Association (ITPA)
    A trade association of companies that buy and sell used and remanufactured heavy-duty truck parts.
    Interpole
    A small field pole placed between the main field poles and electrically connected in series with the armature of an electric rotating machine.
    Intrinsically Safe
    A system that is incapable of releasing sufficient electrical or thermal energy under any condition to cause ignition of a specific hazardous mixture in the atmosphere, even in its most ignitable concentration.
    Inversion Valve
    A normally open air valve used primarily in parking and emergency brake systems.
    Investigation Table
    A term used for component location table.
    IOE
    An abbreviation for intake over exhaust.
    Ionic Bond
    A primary bond arising from the electrostatic attraction between two oppositely charged ions, such as electrostatic painting.
    IROC
    An abbreviation for International Race of Champions.
    Iron
    A basic element with the chemical symbol Fe.
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