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Motorcycle Glossary of Terms


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Damper - Used for slowing down movement in suspension system or as a crankcase balance.

Daytona - The infamous Daytona Bike Week held late February to early March in the USA.

Decarbonisation - The process of removing carbon deposits - typically from the combustion chamber, valves and exhaust port/system.

Diode - An electrical valve which only allows current to flow in one direction. Commonly used in rectifiers and starter interlock systems.

Direct current (dc) - Current produced by a dc generator.

Disc valve (for rotary valve) - An induction system used on some two-strole engines.

Displacement - The engine capacity or amount of volume displaced by the movement of the piston from bottom dead centre to top dead centre.

Distributor - A gear driven contact sending high tension current to spark plugs.

Dope - Highly combustable alcohol/methanol-based fuel mixture.

Double-overhead camshaft (DOHC) - An engine that uses two overhead camshafts, one for the intake valves and one for the exhaust valves.

Drivebelt - A toothed belt used to transmit drive to the rear wheel on some motorcycles. A drivebelt has also been used to drive the camshafts. Drivebelts are usually made of Kevlar.

Driveshaft - Any shaft used to transmit motion. Commonly used when referring to the final driveshaft on shaft drive motorcycles.

DSA - Driving Standards Agency.

Dual sport - street-legal bikes that provide varying levels of off-road capabilities.

DVLA - Driver and Vehicle Licensing Agency. The agency you need to apply for a driving license.

DVLC - Driver and Vehicle Licensing Centre.

Dry sump - Two oil pumps, one supplying oil to the bearings from a tank, the other to return it to the tank