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REF-24
Technical Terms Explained
A
ABS (Anti-lock braking system) A system,
usually electronically controlled, that senses
incipient wheel lockup during braking and
relieves hydraulic pressure at wheel which is
about to skid.
Aftermarket
Components suitable for the
motorcycle, but not produced by the motorcycle
manufacturer.
Allen key A hexagonal wrench which fits into a
recessed hexagonal hole.
Alternating current (act Current produced by
an alternator. Requires converting to direct
current by a rectifier for charging purposes.
Alternator
Converts mechanical energy from the
engine into electrical energy to charge the
battery and power the electrical system.
Ampere (amp) A unit of measurement for the
flow of electrical current. Current
= Volts. Ohms.
Ampere-hour (Ah) Measure of battely capacity.
Angle-tightening
A torque expressed in
degrees. Often follows a conventional tightening
torque for cylinder head or main bearing
fasteners (see Illustration).
Angie-tightening cylinder head bolts
AntIfreeze A substance (usually ethylene glycol)
mixed with water, and added to the cooling
system, to prevent freezing of the coolant in
winter. Antifreeze also contains chemicals to
inhibit corrosion and the formation of rust and
other deposits that would tend to clog the
radiator and coolant passages and reduce
cooling efficiency.
AntI-dive System attached to the fork lower leg
(slider) to prevent fork dive when braking hard.
Anti-seize compound A coating that reduces
the risk of seizing on fasteners that are subjected
to high temperatures, such as exhaust clamp
bolts and nuts.
API
American
Petroleum
Institute.
A quality
standard for 4-stroke motor oils.
Asbe8to8
A natural flbroos mineral with great
heat
resistance,
commonly
used
in
the
composition of brake friction materials. Asbestos
is a health hazard and the dust created by brake
systems should never be inhaled or ingested.
ATF Automatic Transmission Fluid. Often used
in front forks.
ATU Automatic Timing Unit. Mechanical device
for advancing
the
ignition
timing
on early
engines.
ATV All Terrain Vehicle. Oft.,
called a Quad.
Axi8I play Side-to-side movement
Axle
A shaft on which a wheel revolves. Also
known as a spindle.
pollutants in the exhaust gua
into less harmful
substances.
Charging
system
Description
of
the
components which charge the battery, ie the
aJtemator, rectifer and regulator.
Clrcllp
A ring-shaped clip used to prevent
endwise movement of cylindrical parts and
shafts. An intemal circllp is installed in a groove
in a housing; an external circllp fits into a groove
on
the
outside
of
a
cylindrical
piece such as a shaft. Also known as a snap-ring.
Clearance The amount of space between two
parts. For example, between a piston and a
cylinder, between a beel'ing and a journal, etc.
Coli apring A spiral of elastic steel found in
various sizes throughout a vehicle, for example
as a springing medium in the suspension and in
the valve train.
Compression
Reduction in volume, and
increase in pressure and temperature, of a gas,
caused by squeezing it into a smaller space.
Comprea8ion damping Controls the speed the
suspension compresses when hitting a b~.
Compre88ion ratio The relationship between
cylinder volume when the piston is at top dead
centre and cylinder volume when the piston Is at
bottom dead centre.
ContirM8iy The unintemJpted path in the tow of
electricity. UtIle or no ~
reIistance.
Continuity t88t8r Self-powered bIeeper or test
light which indicates continuity.
Cp Candlepower. Bulb rating common found on
US motorcycles.
Croaspty tyr.
Tyre plies arranged in a
criss-cross pattem. Usually four or six plies used,
hence 4PR or 6PR In tyre size codes.
Cuah drive
Rubber damper segments
fitted between the rear wheel and final drive
sprocket to absorb transmission shocks (He
11118b'8tion).
B
Seckla8h The amount of movement between
meshed components when one component is
held still. Usually applies to gear teeth.
8811 beerlng A bearing consisting of a hardened
inner and outer race with hardened steel balls
between the two raoeB.
BeeFing. Used between two working surfaces
to prevent wear of the components and a build-
up of heat. Four typea of bearing are commonly
used on motorcycles: plain shell bearings, ball
bearings, tapered roller bearings and needle
roll« bearings.
Bevel gurw Used to tum the drive through 900.
Typical applications are shaft final drive and
camshaft drive (S88 iUU8b'ation).
Bevel gears are used to turn the drive
throughSO-
BHP
Brake
Horsepower.
The
British
measurement
for engine power output. Power
output is now usually expressed
in kilowatts
(kW).
&i.a-belted
tyre
Similar construction
to radial
lyre. but with outer belt running at an angle to the
wheel rim.
Big-end bearing The bearing in the end of the
connecting rod that's attached to the crankshaft.
Bleeding The process of removing air from an
hydraulic system via a bleed nipple or bleed
screw.
Bottom-end
A description of an engine's
crankcase components and all components
contained there-in.
BTDC Before Top Deed Centre in teImS of pi8ta1
position. Ignitk)n timing Is ~
e)Cpr888ed i1 t8ms
of degoees or miIIimetr. BlOC.
Bush A cylindrical metal or rubber component
used between two moving parts.
Burr Rough edge left on a component after
machining or as a rMUlt of excessive weer.
Cush drive rubbers dampen out
transmission shocks
D
c
Degree disc Calibrated disc for measuring
piston position. Expressed in degrees.
Diet gauge Clock-type gauge with adapters for
measuring runout and piston position. Ex~
in mm or inches.
Diaphragm The rubber membrane in a master
cylinder or carburettor which seals the upper
chamber.
Diaphragm spring A single sprung plate oft.,
used in clutches.
Direct current (dc) Current produced by a dc
generator.
C8n chain The chain which takes drive from the
crankshaft to the camshaft(s).
Canister The main component in an evaporative
emission control system (California mart<et only);
contains activated charcoal granules to trap
vapours from the fuel system rath. than allowing
them to vent to the stmosphere.
CastelI8t8d Resembling the parapets along the
top of a castle wall. For example, a castellated
wheel axle or spindle nut.
C8talytic converter
A device in the exhaust
system of some machines which converts certain
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