Hi Martin,
I’ll try and bypass any possible confusion over models and years by talking about dimensions.
I think the first thing to ask is whether your crankcase is physically appropriate for your frame. Does it fit? If you are happy with the crankcase and intend to use it then you need to establish what crank type it takes.
If the main bearing cup is 2” ID then it requires a crank with a 7/8” diameter where the gland fits. If it’s a 2 1/4” ID then it requires a crank with a 1” diameter where the gland sits.
I think that stands.
So there are quite a lot of details to add to that to be certain that what you have got will work. A crankcase with a 2 1/4” ID bearing cup could originally be a short stroke or long stroke engine. The easiest way to tell this is from the engine number. A short stroke crankcase with a 2 1/4” ID crankcase cup can be fitted with long stroke cranks, rods, block but may need a little fitting work/ machining to get everything to fit.
Long stroke engines were not made with 7/8” crank diameters.
Short stroke cranks were made with 7/8” crank diameters and 1” crank diameters.
Short stroke engines were made with two main types of crankcase:
The early sloping back cases in conjunction with the two speed gear or the three speed wobbly walking stick type gearbox.
The later ‘square back’ design.
There’s a lot of extra information of course… but maybe this is useful to you.
Best wishes,
Richard
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