Pre-unit construction

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Pre-unit construction is a term used to describe motorcycle engine architecture where the engine and gearbox are separate casings, with their own oil reservoirs, usually attached to parallel plates that also attach to the frame. In the 1950s technical advances meant it was possible to reliably construct engines with integral gearboxes in one unit, known as Unit construction. Another variant is Semi unit construction, where the gearbox is bolted directly to the engine.