Unit Construction
Engines and gearboxes were originally separate items, the gearbox being driven by a "primary chain". Later designs combined the two elements into a single "unit construction". Some manufacturers, such as Norton and Enfield continued with "pre-unit" construction until recently, and Harley-Davidson still makes pre-unit engines today.
In the early 1960s, BSA introduced new short-stroke unit construction 500 and 650 cc parallel twins to replace their existing pre-unit long-stroke engines. Triumph modified their large pre-unit 500 and 650 cc parallel twins into unit-construction engines. The smaller Triumph 350 and 500 cc twins had been unit construction from their introduction in 1957. The decision by Lucas to discontinue making dynamos and magnetos, and to produce only alternators and coil ignition systems, was a significant factor in forcing the redesign.
Traditionally, engines and gearboxes had separate lubrication systems with different grades of oil; but modern practice is to use the same oil for both.
Read more about this topic: Motorcycle Engine
Famous quotes containing the words unit and/or construction:
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