Head question... F versus K

[dave Esch]

Is the head from an F bike interchangeable with the bottom end of a K bike? Does anyone know the difference between the two late 70's  750 four models??? I basically want to pull the head off my K, remove the valves, rockers and springs well, everything, and use it all with the F head.

[Piute]

             With my F2 is not just a swap to any other 750 ,f2 is bigger,
           Don't have speks off the top of my head ,
           but through the search can be found I posted it.for this reason.
                                             

[Piute]

 here ya go dav.http://honda-cb750-s.456789.n3.nabble.com/K-series-vs-late-F-series-td3580295.html

[shinyribs]

From what I understand,the SOHC heads are interchangeable.The F head has slightly larger valves.The F also has a different compression ratio,i dont know if that is achieved with the piston or different size combustion chamber in the head.Also the cams are a bit more upper rpm range suited,so if you have a complete F head it has a little different cam in it.I believe I am correct on those details,but regardless, I dont see why any SOHC head/bottom ends won't interchange.

[Re-run]

The later 77/78 heads had different oiling that the earlier k heads did not have.
I will need to check on it but for now, stick with 70-76 and 7-78 for years on the heads.

[Piute]

 Sorry maybe
 Maybe my link gave you to much info
was copied wrd 4 wrd for eng. mod.
 BUT, from it you can see ; A straight swap is not possible with out making larger valve holes,witch is very critical of these machines...,that would be using "F" parts in "K" head as you were asking ?
 
  This brings me to A  ? (wake up ShinyRibs 1st part Chevy)on A 350sml block you can put so 327 heads on it and bring up the compression ratio,people do that all the time(ole Indian trick)
  So would that work putting complete head from A "K" on A "F" ,Smaller combustion chamber ??
   

  Sorry Dav. but good points here;  Cause IF it ("K" heads on "F")brings up compression then would drop compression if "F" heads on "K" RIGHT ,were talking no mods just bolt on ??????????
 

[shinyribs]

Right Piute.But I dont know what is changing the compression between the K and the F model.I dont know if it is the head or the piston.

[Piute]

  The Prob. I'm speaking from past reads is If you put on A Wesco 836 kit on A "F2"or"F3" you would loose compression,due to the BIGGGER head combustion size, So (now)there are companys that make that differents with BELIEVE " piston " that will bring that compression up ,"this is my understanding " from Eng.mods info.

[Re-run]

The head design on the 77/78F is what changes the compression. The F2/3 pistons were domed to make up for this.

[Lucky 1]

Ask Cycle -X

Yes it will work. Here is a Photo from the Cycle X website of a F2 head on a K bottom end.


But....the HOW is what you need to know.

[shinyribs]

Ok,so the combustion chamber IS what changes the compression ratio in this instance. Thanks guys

[Re-run]

Only way this will properly work though is if you have the oil galleys in the cylinder block to match the galleys in the head. That is where the early and post 76 differ mainly, well aside from the difference F2 valves.
Almost any other engine change can be fitted to any model.

[Lucky 1]

Yes the oil galley drains would need to be blocked and  the valves could hit the edges of the cylinder walls . The head gasket would have to have clearance and be thicker?
Lots of considerations that I do not know the particulars about.

[dave Esch]

I'm not sure the year of the replacement head. To be honest, I'm not sure of the year of my motor. The VIN's don't match between bike and my motor. The engine is at work so I will see if I can determine what year it is by the VIN.

[TOOLS1]

Give me the vin, and I can tell, you what your engine is. Also the engine numbers never matched the frames.
TOOLS

[dave Esch]

Really? That's news to me, I didn't know that. I wish i knew that. I actually had a buyer last year that backed out of the sale because the numbers didn't match. Wait, maybe I'm glad, if I knew that I would've sold it!