Dictionary of Automotive Terms: M

MACPHERSON STRUT: Front end suspension system in which wheel assembly is attached to a long, telescopic strut. Strut permits wheels to pivot and move up and down. Strut also acts as a shock absorber.

MAG: Magneto.

MAGNAFLUX: Special chemical process used to check parts for cracks.

MAGNET (Permanent): Piece of magnetized steel that will attract all ferrous material. Permanent magnet does not need electricity to function and will retain its magnetism over a period of years.

MAGNETIC CLUTCH (Air Conditioning): Electromagnetic clutch that engages or disengages air conditioning compressor pulley.

MAGNETIC FIELD: Area encompassed by magnetic lines of force surrounding either a bar magnet or electromagnet.

MAGNETO: Engine driven unit that generates high voltage to fire spark plugs. It needs no outside source of power such as battery.

MAGS or MAG WHEEL: Lightweight, sporty wheels made of magnesium. Term mag is often applied to aluminum, and aluminum and steel combination wheels.

MAIN BEARINGS (Engine): Bearings sup porting crankshaft in cylinder block.

MAIN BEARING SUPPORTS: Steel plate installed over main bearing caps to increase their strength for racing purposes.

MAIN DISCHARGE TUBE: Carburetor fuel passage from bowl to air horn.

MANDREL: Round shaft used to mount stone, cutter, saw, etc.

MANIFOLD: Pipe or number of pipes connecting series of holes or outlets to common opening. See Exhaust and Intake Manifold.

MANIFOLD HEAT CONTROL VALVE: Valve placed in exhaust manifold, or in exhaust pipe, that deflects certain amount of hot gas around base of carburetor to aid in warmup.

MANOMETER: Instrument to measure pres sure (vacuum).

MANUAL CONTROL VALVE (Transmission): Hand (linkage) operated valve which controls oil flow and transmission gear selection.

MASTER CYLINDER: Part of hydraulic brake system which pressure is generated.

MASTER ROD (Radial Engine): Primary or main connecting rod to which other connecting rods are attached.

MATTER: Substance making up physical things occupying space, having weight, and perceptible to the senses.

MECHANICAL BRAKES: Service brakes that are actuated by mechanical linkage connecting brakes to brake pedal.

MECHANICAL EFFICIENCY: Engine’s rating as to how much potential horsepower is wasted through friction within moving parts of engine.

MECHANICAL FUEL INJECTION: A mechanically driven pump forces fuel into engine.

MECHANICAL FUEL PUMP: Engine mounted pump operated by eccentric device.

MEGOHM: 1,000,000 ohms.

MEMA: Motor and Equipment Manufacturers’ Association.

MEP: Mean Effective Pressure. Pressure of burning fuel (average) on power stroke subtracted by average pressure on other three strokes. Pressure is in pounds per square inch or kilopascals.

MESH: To engage teeth of one gear with those of another.

METAL FATIGUE: Crystallizing of metal due to vibration, twisting, bending, etc. Unit will eventually break. Bending a piece of wire back and forth to break it's a good example of metal fatigue.

METERING ROD: Movable rod used to vary opening area through carburetor jet.

METERING VALVE (Brakes): Valve in brake line that limits fluid pressure to disc brakes. This assures that the rear (drum) brakes apply at about the same time as front (disc) brakes.

METRIC SIZE: Units made to metric system measurements.

METRIC SYSTEM: A decimal system of measurement based on meter (area, length, volume), liter (capacity), and gram (weight and mass).

MICRO: When the word “micro” precedes measurement units, such as watt, ampere, etc., it means one-millionth of that unit.

MICROFARAD: 1/1,000,000 farad.

MICROMETER (Inside and Outside): Precision measuring tool that will give readings accurate to within fraction of one thousandth of an inch.

MIKE: Either refers to micrometer or to using micrometer to measure an object.

MILL: Often used to refer to engine.

To remove metal through use of rotating toothed cutter.

MILLIMETRE: Metric measurement equivalent to .039370 of an inch.

MILLING MACHINE: Machine that uses variety of rotating cutter wheels to cut splines, gears, keyways, etc.

MISFIRE: Fuel charge in one or more engine cylinders which fails to fire or ignite at proper time.

MODULATOR (Transmission): Pressure control or adjusting valve used in hydraulic system of automatic transmission.

MOLD: Hollow unit into which molten metal is poured to form a casting.

MOLECULE: Smallest portion that matter may be divided into and still retain all properties of original matter.

MONOBLOCK: All cylinders cast as one unit.

MOTOR: Electrically driven power unit (electric motor). Term is often incorrectly applied to internal combustion engine.

MOTOR (Generator): Attaching generator to battery in such a way it revolves like an electric motor.

MPH: Miles per hour.

MUFFLER (Exhaust): Unit through which exhaust gases are passed to quiet sounds of running engine.

MUFFLER (Air Conditioning): Device which reduces pumping noise and vibration in system.

MULTIPLE DISC CLUTCH: Clutch utilizing several clutch discs in its construction.

MULTI-VISCOSITY OILS: Oils meeting SAE requirements for both low temperature requirements of light oil and high temperature requirements of heavy oil. Example: (SAE 10W-30).

MUTUAL INDUCTION: Creating voltage in one coil by altering current in another near by coil.

MVMA: Motor Vehicle Manufacturers Association.