Tappet shims are measured with a micrometer

MON (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: 778