A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
M
M.O.T: Ministry of Transport. Colloquial for the annual inspection test for vehicles.
MAF: Mass Air Flow Meter.
Magnet: Any material with the naturally occurring phenomenon that has the ability to attract iron.
Magnetic Field: The magnetic shape made up from the force lines around a magnet.
Magnetic Flux: The force contained in a magnetic field.
Magnetic Pole: The ends of a magnet where the lines of force originate. The north and south poles.
Magnetic Pulse Generator: A sensor that uses an iron core and electrical winding to induce an electrical current when passed by a toothed wheel or rotor. Also known as an inductive generator.
Magnetic Stand: A holding device for measuring equipment such as a dial test indicator.
Magnetism: A natural force found in iron and some other materials.
Magnitude: The height of a wave. The maximum voltage in an AC wave pattern.
Main Beam: The upper of the two headlamp beams. Also driving beam and upper beam.
Main Bearings: Central journals and bearings on a crankshaft axis mounted in the engine crankcase. The crankshaft rotates in these bearings.
Main Gallery: A tube shaped section cast in to the engine block where other oil feeds are taken from.
Mainline Pressure: The regulated hydraulic pressure in an automatic transmission.
Malleable: Describes a material that means it can be easily shaped.
Mandrels: Bars used to locate a component.
Manifold: Pipes or ducting to route air in or burnt gases out of an engine. Attached to the ports.
Manifold Absolute Pressure: The mean gas absolute static pressure in an engine induction manifold. Absolute pressure is equal to gauge pressure plus atmospheric pressure.
Manifold Vacuum: The depression or low pressure that occurs in the inlet manifold due to the increasing volume above the pistons when they are moving downwards in the cylinders. The airflow into a naturally aspirated engine cannot move quickly enough to fill the additional volume and therefore loses pressure and density.
Manual Transmission: Transmission system where the driver makes the gear shifts by means of a control (gear) lever and linkages to the gearbox.
Manual Valve: The gear selector valve in an automatic transmission operated by the driver.
MAP: Manifold Absolute Pressure Sensor. The mean gas absolute static pressure in an engine induction manifold.
Map Light: Small light used in a vehicle for illuminating a map!
MAP Sensor: A pressure sensor used to measure manifold absolute pressure in an engine induction system.
Mass: The total theoretical weight of matter based on its atomic structure. The weight of matter without gravitational pull.
Mass Air Flow Meter: A sensing device in the air intake duct of a fuel injection engine that provides data for control of the quantity of fuel that is injected.
Master Cylinder: The pump on a brake hydraulic system.
Matter: A term used to describe any substance as a 'quantity of atoms'.
McPherson Strut: Telescopic independently sprung suspension member incorporating a damper, and fixed at its upper end to the body. The lower end is located by linkages which counteract transverse and fore and aft movement. The original system used a track control arm for transverse forces and an anti-roll bar for longitudinal (fore and aft) location. Usually incorporated in a steered front suspension system.
Mechanical Advantage: The effectiveness of a simple machine, such as a lever, inclined plane, wedge, pulley system or a screw at amplifying a force.
Mechanical Efficiency: The ratio between the actual total output of a machine and the theoretical maximum output.
Memory: The stored data in a microcomputer or electronic control module.
Memory Keeper: A battery or secondary power source used to preserve ECU memories when the main battery is disconnected. It can often be plugged in to the cigar lighter socket.
Memory Saver: A battery or secondary power source used to preserve ECU memories when the main battery is disconnected. It can often be plugged in to the cigar lighter socket.
Mesh: Criss-cross fibres to produce a material with very small holes. Used to make filter elements.
Mesh (Gears): Gear teeth in contact.
Meter: Measuring the flow rate of a gas or liquid.
Metering: When applied to fuel systems a control device for achieving the correct air/fuel mixture strength for specific engine running conditions.
Metering Needle: See metering rod.
Metering Ports: Ports designed to a set size to allow accurate flow of fuel or air.
Metering Rod: A tapered needle in a jet in a carburettor. The taper allows a varied or metered supply dependent on the position of the taper in the jet.
Methanol: Methyl-alcohol used as a fuel or fuel additive.
Metric: European standards of measurement based on the metre.
MFI: Multipoint fuel injection. Usually known a port fuel injection or multipoint fuel injection (MPI).
Micro Processor: A processor on a single integrated circuit or chip. The calculator in a microcomputer or electronic control module.
Micro Switch: A small switch usually operated by a moving mechanism.
Micro-porous: Containing lots of very small holes.
Microelectronics: Refers to integrated circuit electronics usually involving some form of processor.
Micrometer: Measuring device based on an accurate screw thread. Measurements can be taken to 0.01mm/0.001''.
Microwave: 1. Essential equipment for use when a technician is hungry...2. High frequency radio waves.
MIL: Malfunction indicator lamp. Dashboard warning light from an electronic control module to signal a system or component failure.
Milling: A machining process that uses a rotating blade to cut through the surface of materials.
Miscibility: The property of materials that mix easily.
Misfire: Uneven running of an engine due to one or more cylinders not working properly.
Misrepresentation: Represent wrongly with false account (legal).
Modem: Modulator-demodulator. Used to convert computer signals so that they can be sent over telephone lines.
Modulating Valve: A valve that can be switched on and off rapidly such as to control its partially open position.
Modulator Assembly: Releases and re-applies fluid pressure to brake units. (ABS). Adjusts and regulates.
Modulator Valve: Flow control valve in power steering pump. In an automatic transmission a valve that responds to manifold vacuum to create hydraulic pressure feedback to the main control assembly.
Module: An electronic control unit for a vehicle system.
Molecular: Relating to atoms formed into molecules.
Molecular Mass: Term used to describe the mass of molecules - usually relating to the mass of the protons and neutrons.
Molecule: Two or more chemically bonded atoms.
Momentum: Force that keeps a body moving.
Monolith: The honeycomb catalyst support element in a catalytic converter.
Monopoint: A petrol fuel injection system using a single point (or monopoint) injector in a throttle body in the inlet air supply and positioned on top of the inlet manifold. Also throttle body injection (TBI).
Motor Reverse Circuit: An electrical circuit that reverses polarity supplied to a motor.
Mounting: General term for the part of a component, or a separate component, which fits one thing to another.
Mounting Studs: Threaded fixings for an exhaust flange or similar.
Mountings: Insulated or solid attachments for components/units on the vehicle. Insulated versions absorb vibration and provide some protection from shock loads.
Moving Conductor: The armature in a motor or dynamo.
MPI: Multipoint Fuel Injection.
Muffler (Silencer): A component in the exhaust system to absorb the gas shock waves and noise in order to reduce the emitted noise from a vehicle engine. Also known as a silencer.
Multi-Plate Brake: A brake that uses several clutch-type plates.
Multi-plate Clutch: A clutch mechanism having a series of friction and steel plates in a clutch drum assembly. One set of plates is splined to the drum and the other to a centre shaft so that drive through the clutch is via the drum, friction faces and the centre shaft.
Multi-vee Belt: A flat drive belt with several ridges or vee shapes running circumferentially (the long way round).
Multigrade Oil: Classification for lubricating oils that change viscosity grades during temperature change. The lower number is the cold temperature grade and the higher number the hot temperature grade. These oils do not thin at the same rate as single grade viscosity oils as the temperature rises. Also known as multi-viscosity oils.
Multimeter: An electrical measuring tool with functions for volts, amps and ohms.
Multiplate: A clutch mechanism having a series of friction and steel plates in a clutch drum assembly. One set of plates is splined to the drum and the other to a centre shaft so that drive through the clutch is via the drum, friction faces and the centre shaft.
Multiplexed: In signal transmission where each set of signal pulses is given a certain time or frequency slot. This allows a great number of individual signals to be carried by a common conductor.
Multiplexer: A unit used for signal transmission where each set of signal pulses is given a certain time or frequency slot. This allows a great number of individual signals to be carried by a common conductor.
Multiplexing: A common conductor system for digital signal transmission where each set of signal pulses carries its own unique identity. This allows a great number of individual signals to be carried by the common conductor.
Multiplug: A connector with more than one electrical terminal inside.
Multipoint Fuel Injection: Gasoline electronic fuel injection system with injectors in each inlet manifold spraying fuel in towards the inlet valves in the ports of each cylinder. Also known as port injection.
Multisockets: Sockets with many positions for fitting over a bolt or nut head. Sometimes described as multihex.
Mutual Induction: The electrical current induced in one conductor because of the electrical current flow and magnetic field produced around another conductor nearby. Used in transformers to induce a current in one winding from the electrical flow of another when both are wound around an iron core to create a magnet field.