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: ''For the vehicle design where the vehicle's skin is used as a load-bearing element, see Monocoque.'' 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 unit construction, the engine and gearbox had their own separate casings and were connected by a primary chain drive running in an oil bath chaincase. The new system used a similar chain drive and both had 3 separate oil reservoirs for engine, gearbox and primary drive. Triumph and BSA were already using cast alloy chaincases and started converting to unit construction in the 1950s. Velocette, Matchless/AJS and Norton motorcycles continued to be pre-unit (the former machines with pressed-steel primary cases) until the end of production in the 1960s and 1970s respectively. ==Advantages and disadvantages== The advantages of unit construction are: *the combined unit contributes to the stiffness of the entire machine, which either handles better or can have a lighter frame. *it is shorter - amongst other things, this means the primary drive is shorter and less troublesome. *engine and transmission are now much more accurately aligned to each other in the frame, improving primary drive life. *better lubricated duplex (and even triplex) primary chains deliver smoother power. *the engine is cleaner in appearance and fashionably modern, by post-war standards. A significant disadvantage is that there is no longer any tension adjustment possible of the chain drive between engine and transmission, and tensioning (which is almost certainly still required) must be over a rubber-faced steel slipper. However, this is quieter and the tensioner does not wear greatly. The change to unit construction marked the end of choosing a gearbox from another manufacturer (e.g. a close-ratio unit for racing) and sending worn gear-box units to specialist re-builders. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Unit construction」の詳細全文を読む スポンサード リンク
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