Evolution of motorcycle crankshafts

In the earliest days machine shops and factories alike had few special-purpose machines so the manufacture of a crankshaft had to be implemented on low-cost general-purpose machines such as lathes, mills and glorified drill presses. This succeeded so long as engine rpm remained low (~2500rpm).

Because rolling bearings survive well on very little oil, they were soon proven to be a better choice than the ubiquitous bronze bushings inspired by long-established 19th century railroad practice.

Most early engines