Topic: Engine Swap - 1973 CB750 K3 Engine in a 1975 CB750 F0 Frame

[Seeparkfly]

So I just bought a CB750 K3 and decided to look for a F0-F1 Super Sport frame, but before I buy I need to know if the engines are interchangeable. I've searched around but couldn't find clear info on the subject.

Is this a direct swap or does this require some extra parts?

Will I run into problems with fitment into the SS frame?

Is it even worth it, or should I rebuild the frozen F0 engine since it has better potential, i.e. better compression and higher redline? (The K3 supposedly has a big bore kit on it though)

Anybody have experience doing this?

[mcpuffett]

Hi the Engines are a straight swap, the only difference i can think of is how the exhaust mounts at the front of the engine, the earlier engine has spigots held on by 2 phillips screws that the exhaust slips over & the FO/F1 uses 2 studs to each exhaust port and colletts to hold the headers in  , hope this helps, cheers Mick.

[Jerry Rxman Griffin aka MuthaF'er]

Direct swap. Use the F cam! 

[Seeparkfly]

Hi the Engines are a straight swap, the only difference i can think of is how the exhaust mounts at the front of the engine, the earlier engine has spigots held on by 2 phillips screws that the exhaust slips over & the FO/F1 uses 2 studs to each exhaust port and colletts to hold the headers in  , hope this helps, cheers Mick.

Thanks Mick! I appreciate the info. The K3 motor has under 8,000 miles. It's been sitting around since 79 but it fired right up! I'm contemplating whether to switch or not. The K3 has a 836 big bore kit on it.. Does that mean it has better potential than the stock F0? I hear the F0 has a higher redline, does the 836 engine rev that high as well?

[Seeparkfly]

Direct swap. Use the F cam!

Man, that's great! I was wondering about using the F cam... How about using the F carb?

[Seeparkfly]

Direct swap. Use the F cam!

So I finally, after way too much time spent on the intarweb, found a 1976 F1 that runs. It has about 35,xxx miles on it. I also have a K3 with an 836 kit on it (previous owner told me so), with around 7,700 miles on it!

I'm planning on using the K3 engine in the F1 frame since Mark told me the transmission on the K3 is much better, and since it has lower miles. However, I want the best of both worlds. What other parts should I pull to put in the K3 engine besides the F1 camshaft?