Topic: '72 cb750 engine into a '78 cb750 frame

[junkyhands]

I've got a '72 cb750, but the frame is unregistered.  i have a lead on a '78 cb750 frame with papers (sohc) and i was wondering if the '72 engine would swap straight in or if I'd need to modify it.  Any thoughts?

Thanks so much!

[brandEn]

Is it a 78 K or F ?
The engine will mount right in no problem. But just so you know the 78 used a 630 chain and different carbs so take that into account. Those could be an issue that needs to be worked out.

[junkyhands]

It's a K model.  I have a fully running '72 K so i can swap the rear wheel and engine onto the '78 frame.  I wouldn't have a problem then, would I?

Thanks for the reply!

[Patrick]

The engine will go into the frame fine, but you will need other parts to make it work. If both bikes are complete, no problem. For the k2 engine, you will also need the k2 sprocket carrier. To go into the '78 frame you will need the '78 axle and spacer.

There are certainly other things I am not remembering right now.

But with two complete bikes, no problem. I did exactly that - a K2 engine in an F3 frame - on my last 750.

Patrick

[junkyhands]

Cool!  Thanks, guys! 

I'm excited to wrench.

[GammaFlat]

Without thinking about it too much, maybe you could run the 72 swing arm on the 78 frame and all alignment would be good.  This way, you could use all the 72 parts on the swing arm (wheel, spacers, sprocket, etc.).  The key is whether the relationship between the swing arm location and engine is the same between the pre-K7 and post K6.