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Motorcycle Glossary of Terms


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ABI - Association of British Insurers.

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.

ACU - Auto Cycle Union, who control a large part of British Motorcycle Sport.

Advanced Ignition - Ignition timing set causing firing before the piston reaches centre top, variation is now automatic.

Aftermarket - Components suitable for the motorcycle, but not produced by the motorcycle manufacturer.

AHRMAL - American Historic Racing Motorcycle Association.

Air-cooling - Many motorcycles rely on air-cooling to the atmosphere.

Air intake - The carburettor port admitting are to mix with fuel from the float chamber.

AJ - Common term for an AJS motorcycle.

Allen key - A hexagonal wrench which fits into a recessed hexagonal hole.

Alternating current (ac)- Current produced by an alternator. Requires converting to direct current by a rectifier for charging purposes.

Alternator - Converts mechanical enery from the engine into electrical energy to charge the battery and power the electrical system.

AMA - American Motorcycle Association.

AMCA - Amateur Motor Cycle Association, promoters of English off-road events.

Ampere (amp) - A unit if measurement for the flow of electrical current. Current = Volts /Ohms.

Ampere-houe (Ah) - Measure of battery capacity.

Angle-tightening - A torque expressed in degrees. Often follows a conventional tightening torque for cylinder head or main bearing fasteners.

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 colling 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 nuts and bolts.

APCO - The Association of Public Safety Communications Officials - International.

Apex - The middle or centre point of a corner.

API - American Petroleum Institute. A quality standard for 4-stroke motor oils.

APMC - The Association of Pioneer Motor Cyclists.

Asbestos - A natural fibrous 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 by inhaled or sigested.

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. Often called a quad.

Auto Cycle Club - Formed in 1903, it was the original governing body of motorcycle sport, in 1907 became the Auto Cycle Union.

Autocycle - A 98cc moped.

Automatic inlet valve - Activated by the engine suction. Forerunner of the mechanically operated valve.

Axial play - side-to-side movement.

Axle - A shaft on which a wheel revolves. Also know as a spindle.


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