Unit Construction - Advantages and Disadvantages

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.