750 twin fitment

I know the twins don't fit into the 4 cylinder frames but why? Would it fit into a 650 csr frame? Obviously new mounts made but is it a size issue?

I wouldn't think so. The 750 Twin engine is narrower & taller. The 650-CSR has the same basic crankcase as a 750-4 & the frame is the same as a 750H Ltd. Just an FYI, there was a 750M CSR that's a twin, so that frame would work. I'd guess you've probably found a 650-CSR frame, but what the heck.

I've built a csr frame but have a 78 to work with. Want to put a twin in it

If you have the engine and frame, test fit it.
I would imagine the spacing between the exhaust headers and the two front frame down tubes may not work so well together, but I could be wrong.
Then there is the drive chain, the front sprocket needs to line up with the back sprocket.

I have seen many builds with an engine swapped into a different frame, even a kawi triple engine into a modern 250 Ninja frame.
Where there is a will, there is a way.

Don't have an engine building a frame looking for the right donor motor

I'm toying with the idea of an Xs650 motor for some crazy suspension design

So, you already had a 650-CSR frame & started modifying it before figuring out the engine fitment?
From memory from a comment by steell in an old topic, I'm pretty sure the 750 Twin engine is too tall for a 650 frame.



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