Motorcycle Glossary of Terms
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Backlash - The amount of
movement between meshed components when one
component in held still. Usually applies to
Ball bearing - A bearing
consisting of a hardened inner and outer race
with hardened steel balls between the two
Balloon tyres - Wide section,
low pressure, soft running tyres, used on
tourers for comfort.
Bathtub - Bodywork resembling
the shape of a bath tub, used mostly on Triumph
Beaded-edge tyres - Encased
rubber beads in channel on wheel trim.
Bearings - Used between
two working surfaces to prebent wear of the
components and a build-up of heat. Four types
of bearing are commonly used on motorcycles;
plain and shell bearings, ball bearings, tapered
roller bearings and needle roller bearings.
Beesa - Common term for
a BSA motorcycle.
Belt drive - A leather or
fabric belt from engine or gearbox to rear
Bevel gears - Used to turn
the drive through 90 degrees. Typical applications
are shaft final drive and camshaft drive.
BHP - A measure of engine
output, eg to lift 33,000lb one foot in a
minute requires one horsepower.
Big end - The larger (crankshaft)
end of the connecting rod.
Bias-belted tyre - Similiar
constuction to radial tyre, 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 a hydrolic system via a
bleed nipple or bleed screw.
BMCRC - British Motor Cycle
Racing Club, formed in 1909.
BMF - British Motorcycle
Bore - The diameter of a
Bore-stroke ratio - Cyclinder
diameter ratio to stroke.
Bottom dead centre (BDC)
- The point during crankshaft rotation at
which the piston is in its lowest possible
Bottom-end - A description
of an engine's crankcase components contained
Bottom out - Occurs when
the suspension travel in maximised and has
no more travel.
BSB - British Superbike
BTDC - Before Top Dead Centre
in terms of piston position. Ignition timing
is often expressed in terms of degrees or
Bush - A cylindrical metal
or rubber component used between two moving
Burr - Rough edge left on
a component after machining or as a result
of excessive wear.