Author Topic: F2 cylinder head to K Conversion (Read 3731 times)

CB750F2 · « **on:** November 07, 2012, 01:10:48 PM »

I am considering replacing the pistons and cylinder head on my CB750 F2 to the K series. I need to know if I can use the the cam towers, cam and valve cover from the F2. Thanks, Pat

Don R · « **Reply #1 on:** November 07, 2012, 01:18:52 PM »

Yes, there is a school of thought the cam is too big for K valve springs. I used a Black engine cam but only have a few miles on it. The rest should fit fine.

CB750F2 · « **Reply #2 on:** November 07, 2012, 01:35:00 PM »

Thanks for your reply. The reason for my asking is because the part numbers for the towers and valve cover uses 410 for the middle three digits - 410 being the model number for the F2. I will check valve to pison clearance using the F2 camshaft. Pat

Jerry Rxman Griffin aka MuthaF'er · « **Reply #3 on:** November 07, 2012, 01:41:57 PM »

You also need to use the F2 cylinders! The F2/F3/K8 springs are stronger so use them.

Cam should not be a problem. Cross reference the tower -410 number and you'll see it fits all 750's.

CB750F2 · « **Reply #4 on:** November 07, 2012, 08:10:24 PM »

Thanks Jerry. However, I am a little confused by " You also need to use the F2 cylinders". I intend to to use my F2 cylinders modified to allow the four inner studs to drain back into the crankcase but surely I could also use a K cylinders if I use a K cylinder head. Pat

Jerry Rxman Griffin aka MuthaF'er · « **Reply #5 on:** November 07, 2012, 08:14:11 PM »

Pat, yeah that was confusing! I need to read better. You gotta use F cylinders with F head and K cylinders with K head when mixing and matching like that. Otherwise you gotta do some mods that can be avoided.

CB750F2 · « **Reply #6 on:** November 07, 2012, 08:18:23 PM »

Thanks Jerry. You had me worried for a while. Pat

Don R · « **Reply #7 on:** November 07, 2012, 09:12:03 PM »

What about the retainers? K or F? on the K valves.

CB750F2 · « **Reply #8 on:** November 07, 2012, 10:14:02 PM »

If I do go with a K head I will be using the K valve springs, valve spring retainers and valve cotters but using the F2 towers, camshaft, rockers and cylinder head cover. I am not 100% sure that one can use an F2 cylinder head cover on a K cylinder head. Jerry mentioned a cross reference - where do I find this. Pat

bryanj · « **Reply #9 on:** November 07, 2012, 11:35:34 PM »

http://www.motogrid.com/pages/OemParts?aribrand=HOM

Jiminy Indy · « **Reply #10 on:** November 08, 2012, 04:23:19 AM »

Just because I'm curious and if you don't mind me asking, why would you want to make the switch to the K-stuff? Any advantages, or just availability? Thanks

Old Scrambler · « **Reply #11 on:** November 08, 2012, 06:50:18 AM »

The F2 cam should be matched with the F2 springs and retainers. The cover is interchangable. K-model pistons and head.......suggestion.......if you are buying pistons to install in a used cylinder......think about a modest overbore. My second-over rebuild has noticably more power in the mid-range.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #12 on:** November 08, 2012, 07:11:31 AM »

Quote from: Don R on November 07, 2012, 09:12:03 PM

What about the retainers? K or F? on the K valves.

F2/F3/K8 (not K7) retainers are interchangeable. The issue here is fitment with the cuts in the valves. The F2/F3/K8 springs are stronger and will work in any 750.

CB750F2 · « **Reply #13 on:** November 08, 2012, 01:56:13 PM »

I have rebored my F2 cylinders to 836 with flat topped pistons. So, the reason for considering the use of a K head is to raise compression. Also my F2 head needs a lot of work - guides, springs and retainers. My research into the F2 valve problems is that they are caused by poor guide material, valve springs that are too heavy and poor design of the retainers. At this stage I am only considering my options. Another option is to purchase the after market dome shaped pistons that are available and refurbish my F2 head. This would be an expensive option and the new pistons may not fit my freshly bored F2 cylinders. Another option would be to find another F2 cylinder in standard bore. I have assembled the top end using one piston and I am in the process of measuring valve to piston clearance to see if I can raise the compression enough using thinner gaskets and some mild milling. I hope that I have answered your questions. Thanks for the replies, Pat

AbbyRider · « **Reply #14 on:** February 08, 2013, 02:52:36 PM »

Pat - I know this thread is a bit old, but came up when I did a search on the exact same topic. How did the swap work out for you? I need to overbore my cylinder block, and figured I'd use the inexpensive 836 kit. I don't want to use my F2 head, as one of the metal intake spigots broke off, and it requires some work to replace. I've got a K2 head, and all the other stuff from the F2 head is in really good shape. Did you end up using the K valves and the F2 springs?

Any advice would be much appreciated. Cheers!

Dwayne

CB750F2 · « **Reply #15 on:** February 09, 2013, 04:11:40 AM »

Dwayne, I am still looking for an early K head so it is still a "work in progress". I recently acquired a F0,F1/K7,K8 head but chamber 3 has some damage and the valves need replacing. It can be fixed but it would be expensive here in Australia. So, I am still looking for a suitable cylinder head. I have advertised on this website. FYI the head that I acquired is marked 392 and the volume of the chambers 1,2 and 4 measure 23cc and 3 - the damaged one - measures 24cc. I also measured the dome of the 392 piston to be 3.2cc.
I also measured the chambers of my F2 head to be 28.5cc and the dome of my standard bore F2 pistons to be 9.35cc.
I haven't helped you much but that is my current situation - waiting and looking. Pat

70CB750 · « **Reply #16 on:** February 27, 2013, 06:29:31 AM »

Pat, excuse my dumb question, but is it possible to fit just K head on F engine? I have the worst F out there - see the K3F link - and instead of getting valves, guides, seat ground etc I could just go with K head - or not?

The bike parts already came with K2 carbs, it would actually help with thsoe rubber carb to head connectors.

Any advice appreciated - before I start throwing money at it.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #17 on:** February 27, 2013, 11:24:01 AM »

The answer is NO. You need to swap the cylinders and pistons too. Now someone will come back and say that you CAN do it but..... you'll be opening a can of worms and it'd be way too much trouble to even attempt.

Pat, if you get an earlier K head please cc it for comparison. It's my speculation the bump in cr from 9 to 9.2 may be do to the head itself. It's funny that my donor K8 392 has pistons marked 392 and the domes are not full like my 75 F 392 pistons. Both are listed as 9.2. But we all know how Honda made early models hotter.

70CB750 · « **Reply #18 on:** February 27, 2013, 11:29:59 AM »

Thank you, I am just trying to figure out the best way to fix it - biting the bullet and going with the valve train replacement can be cheapest in the long run.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #19 on:** February 27, 2013, 11:35:00 AM »

I know you didn't mention names but APE can redo your F2 head with all new stuff and be done with it. Sometimes hard to bite that bullet but MUCH easier and better outcome. All it takes is one of those money trees

CB750F2 · « **Reply #20 on:** February 27, 2013, 12:48:24 PM »

70CB750, Jerry is correct. You cannot simply fit a K head to F2 cylinders and F2 pistons. In my case I have bored out my F2 cylinders and using flat topped pistons so a K head will work for me. I will have to modify the unused drain back holes on the F2 cylinders to allow oil to drain back into the crankcase - not a big job.
Jerry, I certainly will be ccing the head and will post my results. Pat

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Author Topic: F2 cylinder head to K Conversion (Read 3731 times)