In Reply to: S90 posted by andy on April 11, 2009 at 11:01:41:
The crank from a 6 volt C90 (1968-83) is the same as your S90.
(in fact, most of the engine is the same - 3-speed gaerset, auto clutch and a milder cam, but otherwise identical)
There are plenty of these engines on ebay for next to nothing, as they don't fit the later 12volt C90.
Happy hunting!!