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Will a cb650 engine fit in a '74 cb750 frame?

nsxguy7

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Hello all. I acquired a nice '74 cb750 frame with title that I have been building into a cafe bike for about the last year now. I've found that CB750 SOHC motors have gotten SCARCE up in my neck of the woods. Does anyone know if the 79-82 CB650 engine can be made to work in my frame? I have a friend with a laser and water jet cutting business, so making mounts is no big deal. I'm just wondering if anyone here has done this swap before. I found a guy on YouTube that put this motor in a CB550, so I'm thinking it just might be possible. Thanks in advance!
 
Anything is possible with enough time, money, cutting and welding. Nothings going to fit so the whole thing is going to be custom made. You will have to watch for chain alignment issues as the 750 and the 550/650 engine are completely different. If you are going to buy an engine might as well buy a 750 engine. If you have a 650 engine then you might as well buy a 650 frame, you will be farther ahead in either way. Transplanting engines takes a lot of time, figuring and manufacturing.
 
A 550 frame is much more amenable to 650 as the 650 began with a 550 blueprint then changed everything. You should have to change more with a 750 frame. I'd look close at height issues inside frame as the 650 goes straight up and mounted in a frame very similar to the bigger DOHC stuff which had a much taller engine as well. The later 650 with CV carbs uses a lot more carb space too. Two different 650 heads there. The 550 /650 transplant would've almost certainly have had to use the '79 head 650 as there is no room for the CVs on one.
 
I put a trail 90 engine in a QA50 frame when I was about 13 ......:cheers:


Hmm, I think it was a Suzuki 2 stroke not a Honda engine.
 
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Weren't 50 thru 90 engine mount centers close to the same though? Maybe redrill a hole here or there.

Engine families come into play there, how you switch 160-200 Honda, 250-400 Kaw, 250-350 Yam, and 750-1100 DOHC with almost bolt in or true bolt in and no custom parts needed. The 650 design started using 550 major points in space and why that was easier.
 
Weren't 50 thru 90 engine mount centers close to the same though? Maybe redrill a hole here or there.

Engine families come into play there, how you switch 160-200 Honda, 250-400 Kaw, 250-350 Yam, and 750-1100 DOHC with almost bolt in or true bolt in and no custom parts needed. The 650 design started using 550 major points in space and why that was easier.

(Christopher Walken voice) No no no, your thinking all wrong here.

Actually I think it was a Suzuki RV90 engine after trying to remember what it looked like. Imagine trying to ride the thing as a little kid. It pulled wheelies in every gear with just a twist of the throttle and I didn't need foot pegs, the engine was so wide I just put my feet on top of the case. :smoke:
 
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