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Tappet shims are measured with a micrometerMON (Motor Octane Number)A measure of a fuel's resistance to knock. Monograde oilAn oil with a single viscosity, eg SAE80W. Monoshock A single suspension unit linking the swingarm or suspension linkage to the frame. mphAbbreviation for miles per hour. Multigrade oilHaving a wide viscosity range (eg 10W40). The W stands for Winter, thus the viscosity ranges from SAE10 when cold to SAE40 when hot. Multimeter An electrical test instrument with the capability to measure voltage, current and resistance. Some meters also incorporate a continuity tester and buzzer. N Needle roller bearingInner race of caged needle rollers and hardened outer race, Examples of uncaged needle rollers can be found on some engines. Commonly used in rear suspension applications and in two-stroke engines. NmNewton metres. NOxOxides of Nitrogen. A common toxic pollutant emitted by petrol engines at higher temperatures. OctaneThe measure of a fuel's resistance to knock. OE (Original Equipment)Relates to components fitted to a motorcycle as standard or replacement parts supplied by the motorcycle manufacturer. OhmThe unit of electrical resistance. Ohms = Volts + Current. OhmmeterAn instrument for measuring electrical resistance. Oil coolerSystem for diverting engine oil outside of the engine to a radiator for cooling purposes. Oil injectionA system of two-stroke engine lubrication where oil is pump-fed to the engine in accordance with throttle position. Open-circuitAn electrical condition where there is a break in the flow of electricity - no continuity (high resistance). O-ringA type of sealing ring made of a special rubber-like material; in use, the O-ring is compressed into a groove to provide the sealing action. Oversize (OS) Term used for piston and ring size options fitted to a rebored cylinder. Overhead cam (sohc) engineAn engine with single camshaft located on top of the cylinder head. Overhead valve (ohv) engine An engine with the valves located in the cylinder head, but with the camshaft located in the engine block or crankcase. Oxygen sensor A device installed in the exhaust system which senses the oxygen content in the exhaust and converts this information into an electric current. Also called a Lambda sensor. PlastigaugeA thin strip of plastic thread, available in different sizes, used for measuring clearances. For example, a strip of Plastigauge is laid across a bearing journal. The parts are assembled and dismantled; the width of the crushed strip indicates the clearance between journal and bearing. PolarityEither negative or positive earth (ground), determined by which battery lead is connected to the frame (earth return). Modern motorcycles are usually negative earth. Pre-ignitionA situation where the fuel/air mixture ignites before the spark plug fires. Often due to a hot spot in the combustion chamber caused by carbon build-up. Engine has a tendency to 'run-on'. Pre-load (suspension) The amount a spring is compressed when in the unloaded state. Preload can be applied by gas, spacer or mechanical adjuster. PremixThe method of engine lubrication on older two-stroke engines. Engine oil is mixed with the petrol in the fuel tank in a specific ratio. The fuel/oil mix is sometimes referred to as "petroil". Primary driveDescription of the drive from the crankshaft to the clutch. Usually by gear or chain. PSPfedestarke - a German interpretation of BHP. PSIPounds-force per square inch. Imperial measurement of tyre pressure and cylinder pressure measurement. PTFEPolytetrafluroethylene. A low friction substance. Pulse secondary air injection systemA process of promoting the burning of excess fuel present in the exhaust gases by routing fresh air into the exhaust ports. Q Quartz halogen bulbTungsten filament surrounded by a halogen gas. Typically used for the headlight (see illustration).
Date: 2016-01-14; view: 981
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