Unit construction

Article summary

: For the vehicle design where the vehicle's skin is used as a load-bearing element, see Monocoque. opposed twin unit construction engine / transmission R32 unit construction engine / transmission Unit construction is the design of larger motorcycles where the engine and gearbox components share a single casing. This sometimes includes the design of automobile engines and was often loosely applied to motorcycles with rather different internal layouts such as the flat twin BMW models. Prior to the adoption of unit construction, the motorcycle engines and gearboxes typically had separate casings and were connected by a primary chain drive running in an oil-bath chaincase. The unit construction design retained a similar chain drive but continued to use separate oil reservoirs for the engine, gearbox, and primary drive. Triumph and BSA were already using cast non-ferrous alloy chaincases and started converting to unit construction in the 1950s. A driving factor behind the BSA/Triumph change was that Lucas had declared an intention to abandon production of motorcycle dynamos and magnetos, and instead produce only alternators. By contrast, Velocette, Matchless/AJS, and Norton motorcycles continued to be pre-unit construction (the former machines with pressed-steel primary cases) until the end of production in the 1960s and 1970s respectively.…

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