'75 CB750 gearbox/transmission in a '78 CB750?

[iannone.nicolas]

QQ:

Just bought a '78 CB750K8 and the transmission &/or gearbox just went out. Found a '75 cb750k5 (complete engine). Is it possible to remove the transmission &/or gearbox from the k5 and bolt it onto the k8? I've searched and searched for the answer to this and can't seem to find the answer.

 

[kerryb]

You should check with/on the SOHC4 forum, you'll have your answer rather quick. Are you sure the k8 is better than the k5? You might be able to make a good engine without splitting the cases. Or just split both open and take the best parts, most of them are interchangeable.

 

[Rider52]

The 77-78 output shaft is 10mm wider than the 75 shaft. Swapping is possible and has been done many times.

 

[Rider52]

I needed to add. Swapping the transmissions will likely cause rear chain alignment issues. The 77-78 swingarm and rear wheel sprocket carrier are also wider than the early models to account of the 10mm output shaft difference. You may need an offset countershaft sprocket or change to an earlier swingarm and sprocket carrier with earlier axle/spacers. The offset countershaft is often the easiest and cheapest to resolve the issue.