Topic: K7 750 cylinder head on a K4. Will this work?

[1974cb550k]

I just bought a head only to find it is off a K7. I have a K4 750, with broken heads on the fins. I want to swap em out. There is no major changes to the head from 74-76 but i am unsure of the K7. Any help here would be great. Thanx
CB750E-2712286 is the engine#

[754]

I cant see a problem,  think the headgasket is the same.. if you want you can pull the studs and put your spigots for the K4 exhaust on that newer head..

[Jerry Rxman Griffin aka MuthaF'er]

If there are no changes from 74-76 then the K7 head should work as Frank says. And the K7 will perform better. It is originally a 75 F head. If you can get the K7 pistons you will get a 0.2 bump in compression too. Just make sure you can find rings for them! While you're at it grab the K7 cam too. You WILL notice an appreciable difference if you use the head, pistons and cam over a K4 engine!

[octagon]

i bought a parts bike a couple of months ago, the po told me he'd recently put a rebuilt head on it. when i pulled the head it was a k7.

[1974cb550k]

Thanx for the input. I already got of cycle x 2ND over pistons. I am worried about valve relief in the pistons. They are diff part numbers (the heads) according of the fiche. I don't really wanna re do a head i cant use. Looking for some more concrete evidence. I will side by side and look at them later in the week. Thanx Btw OCTAGON what year was that parts bike?

[octagon]

it was a 74. he put a few hundred miles on the head with no problems with the fitment.

[Jerry Rxman Griffin aka MuthaF'er]

The 75 F was the first bike to use the "new" head (not to be confused with the 77/78 F which is definitely different and will NOT work). It will probably have "392" cast onto the top fin intake side between #2 and #3. The 76 F also used this head as well as the 77 and 78 K's. You will notice the different appearance of the combustion chamber in that it has been smoothed out as compared to the 74 K head. The 77 part number will be xxxxx-392-xx. It will work better than fine on a 74 engine as it is an upgrade. The 78 K used this head but with different keepers, stronger springs and same size valves with different slots for the different keepers. The valves in the 74 and the 77 are the same. Will not be a problem unless you use a serious lift cam. Call CycleX and ask them if you can use the -392 head with their pistons. 2nd over shouldn't create an issue. You are building a basically stock engine.

[1974cb550k]

Thanx Griffin for the info. It is indeed a "392" head. Going basically stock  is correct I'm going to re use the cam from my 74 head etc. Do you know if the oiling holes in the line up and if there will be a need to shorten the head stud sealing towers? I have also been using the search function but it has a lot about the later F heads on earlier K models, not so much what i need for info but I'm still lookin.

[Jerry Rxman Griffin aka MuthaF'er]

Everything should work fine. Do NOT even look at the later F2/F3 head stuff! It won't work without some serious mods and will just cloud the issue. I really hate to see you reuse that cam. Probably the slowest cam Honda ever put in a 750 but I know how decisions have to be made sometimes. Won't be a problem with lining up oil holes since neither are the F2/F3 head but I can't say for sure when Honda began using the sealing washers around the dowels in the K heads. I do know the 77 K had them. "Shorten the head stud sealing towers"?? Not sure what you are referring to. Are you using a parts catalogue or online fiche? How about using the terminology from one of these so I can go to mine and see what you are referring to. Try this http://www.motogrid.com/pages/OemParts?aribrand=HOM You can check terminology, see which bikes use a particlular part by the part number, look at each bike's parts diagram and get part numbers  to cross reference between the 2 etc. not to mention nice exploded graphics/pictures

[1974cb550k]

I was referring to #2 and or #3 in the fiche from this http://www.xtremeusa.com/fiche_section_detail.asp Either the knock pin or gasket. I was reading somewhere that these might have to be trimmed to get a proper fit. I was also wondering if you could get a 77k with a black painted head from the factory? At first I thought it was a spray bomb but when I cleaned the new head in the parts washer today clearcoat came off. Also are you positive they never used a 392 head on an F2 or F3? Thanx much for all the help. Attached is the link to the head as i purchased it off eBay.
http://www.ebay.com/itm/230733850909?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

[1974cb550k]

The fiche didnt come up here is the part #12116-300-000 pin special knock 12mm as honda calls it. Or the 12115-300-000 packing cyl stud bolt. Taken from the honda parts manual.

[1974cb550k]

Update... the knock pin, and the stud bolt packing are same part#s. The 75-76 F and the 77-78K use the 392 head. The F2-F3 heads use the 410 head. I am now ready to believe that this head will work. That being said the reason I was going to use the stock cam is, that i do not want to replace the cam chain as the lower cases have already been painted. I do not want to use a master linkcam chain and definitely do not want to split the cases. I did not want to put added stress on the cam chain but if it was a stock cam from a 77k that would prob be fine. I would have to swap towers, rocker arms, and the cam to prevent uneven wear. Do you think it would be worth the extra $$ and effort for the gain I might get? Thanx again for the help.

[Jerry Rxman Griffin aka MuthaF'er]

OK, now I know what you mean. I call them dowels but officially they are knock pins. Easier for me to remember. If you will cross reference the cylinder part number in that picture you will see that the cylinders works for/is the same part number as the K4 also. Therefore your 392 head will work with your cylinders. Be careful and use the correct length knock pin as you will see that #11 is also 12mm but 18mm in length. These knock pins are still available if you need new ones or buggered yours up getting them out. I just put my top end together about 1 month ago and bought new knock pins since they were chewed up and distorted from my pliers so it's still fresh in my mind.  The packings or sealing washers as I called them will be fine as is. No trimming. They seal the oil return. The 77/78 K ONLY came painted silver. That one has been repainted black just as I did mine. The 77/78 F head is/has a 410 where our 392 is plus the 410 has 34mm intakes and 32mm exhaust valves. Ours are 31mm & 28mm.

The only way one could interchange 75/76F or 77/78K stuff (they are the same) with 77/78 F is to replace everything from the top case half up basically because the oil returns in the head and cylinders, pistons, head and valves are different and must be done as matched sets.

Knock pins on cylinders awaiting packing washers. heavy duty cylinder studs. you will also notice that the cylinder sleeves are not notched out and they incroach into the sealing packing washer's space. This cylinder has been resleeved for 67mm pistons. I was told that I didn't need the packing washers and they weren't notched when the cylinder was redone. I wasn't happy with that and had my local machine shop cut the notches because I wanted to use them to insure less of a chance for oil leaks.



See if you can get into my Honda folder in my Photobucket acct through that picture and check out what I've been up to.

http://s233.photobucket.com/albums/ee84/RxmanGriff/Honda/#!cpZZ1QQtppZZ28

[Jerry Rxman Griffin aka MuthaF'er]

You can replace the cam without doing anything to the cam chain and you would not need to replace anything else. If you went aftermarket high lift cam then I'd definitely use stronger springs but any stock Honda cam will work with all your existing hardware. The cam is kinda tricky to feed back in. Be sure that the cam goes through the chain first then the sprocket. IE cam's sprocket flange and sprocket with the cam chain in between the 2. IE feed the cam through the chain with the sprocket last and on the outside of these 3 pieces. Point the sprocket's bevel toward the cam sprocket flange too. Put the cam chain on the sprocket then slide the sprocket, beveled side, onto the cam. Kinda had to visualize from print. Wish I did a picture of that! Otherwise you won't get the cam chain on. 

[754]

 use a tap to pull the dowel pins, better than gurfing them with pliers..

[1974cb550k]

You got some nice stuff happenin there Griffin. Looks like this ain't ur first rodeo. I guess you sold me on a cam set up. It would be a shame to let that 2ND over bore to go to waste without giving it some more air. If you know of a set (cam,tower,rockers, bolts etc) that was correctly numbered, when removed and good shape lemme know. Ill be lookin on the feebay. As far as re-insertion of the cam that will be a while (gonna buy an new one now). I have built many 550 500's but this is my first top end on a 750. I had over two hrs and a lot of swearing on my first 550 camchain reinstall. The front cam chain guide was brittle, it slowly ripped apart into black plastic chunks, then broke in half while i was doing 70mph. Bent every valve in the head. Chain never broke though. Thanx again