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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 gear teeth.

Ball bearing - A bearing consisting of a hardened inner and outer race with hardened steel balls between the two races.

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 motorcycles.

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 wheel.

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 Federation.

Bore - The diameter of a cylinder.

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 position.

Bottom-end - A description of an engine's crankcase components contained there-in.

Bottom out - Occurs when the suspension travel in maximised and has no more travel.

BSB - British Superbike Champioship.

BTDC - Before Top Dead Centre in terms of piston position. Ignition timing is often expressed in terms of degrees or millimetres BTDC.

Bush - A cylindrical metal or rubber component used between two moving parts.

Burr - Rough edge left on a component after machining or as a result of excessive wear.