Topic: Confused about Head and Cylinder compatibility CB750 F2 vs K

[NWrider]

There have been a number of posts over the past few days about replacing the F head with a K head. I'm confused about what works and what doesn't.

I have a 1977 F2 engine with 12K on it which needs exhaust valve guides. If I repair the head, I still need to replace the rings which are costly and have not done anything to improve the valve wear problem.

I have a 1976 K engine which (if all or some parts are compatible) I could use for the head, cylinder barrel and pistons with the intent to resolve the issue of premature valve guide wear on my F2.

The confusion is, there are several posts that "this swap requires the K cylinder barrel, head and pistons".

There are several posts that "a K head can be used to replace the F2 head on an F2 cylinder barrel if you swap the K pistons too".

There are posts indicating "the K head will fit, but cause problems".

There are posts that the K cylinder barrels won't fit the F2 engine.

Perhaps it is the details of the particular years associated here. Can I get some consensus so I can determine how I can proceed with getting the bike running?

Thanks.

[Triffecpa]

the F2 engines uses domed pistons and larger combustion chambers and valves than the K engine.  So if you swap a K head onto a F motor, you will get really high compression ratio.  If you put a F head on a K model engine, you will get really low compression.

Swap the head and cylinder and pistons from the K model over to the F bottom and and you're golden.  Basically you've got a K model motor with the stronger bottom end of the F motor.  Valves and pistons and rings are all now easy to find and fairly inexpensive.

TR

[Jerry Rxman Griffin aka MuthaF'er]

Ditto. Swap everything above the top case and use heavy duty studs.

[rbmgf7]

check the Engine FAQ for more. if you swap just the head, regardless of pistons/chamber, you'll run into oil drainage problems and that would be a big uh oh.

[NWrider]

While I am thankful for the responses, there are still mixed responses about what will work.

In the Engine FAQ the following was posted...

"Bottom line....early/late K and early F1(75/76) heads will work on late (F2/F3) cylinders and early/late K and F1 upper cases with mild opening (joining) of the F2/F3 two inner drain back holes at the base of the cylinder."

There appear to be differences in the two heads, but I still don't understand what problems exist if I place the K head on a K cylinder barrel on an F engine base. If it fits, it seems it should match up?

It appears the drain holes must be changed, can anyone explain that difference in enough detail to make it work?

Does the F2 engine base have the heavy duty studs mentioned, as a standard part?

Any harm in painting the K cylinders and head black to match the OEM F look?