I’m just trying to solve the problem with my engine. When I got the bike, engine was in parts and one connecting rod was missing. But what I realized was the long stroke cylinders and short stroke crankshaft. I decided to go easier way and got the long stroke crankshafts and connecting rods. Before I brought all the parts to the guy here who is reconditioning the engine, I realized that the diameter of the shafts is different, shorts stroke has 22,17 mm, long stroke 25,35 mm. Long stroke shafts should be from about 48 engine, but does it exist smaller diameter long stroke shafts? When was the change made? As I know, 2 speed models had usually smaller shafts, so are my short stroke shafts from 2 speeder? Or was 27 engine some in between version still using small shafts?
I would be happy to know a bit more about this. Thanks,
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.
yes, frame fits the engine, it’s 1927 3 speed Flyer type, so the cases with strait back part of the cases, 27/28 type.
Thanks a lot for all information, this throws a lot of light and seems to be possible to fit the crankshaft to the cases.
Happy to help, Martin.
I do have some compatible short stroke engine components that I have available: Crank,rods,barrel… so if that’s of interest, send me a pm…