Topic: 1971 cb 750 cylindar head

[pablo63]

Good day
   I am re-building my 1971 honda cb 750 and recently purchased a gasket set which included the cylinder head gasket , what I found was that the head gasket maybe it's for a later model where I beleive more o-rings were used between the the block and the cylinder  head , the 1971 only used two o-rings , I have gone ahead and   used this gasket only using two o-rings but now am having second thoughts whether I should change it out before putting the engine back in the bike ,has anyone come across this problem and would this gasket be ok .

Thx, Paul

[Kevin D]

Well, first off Pablo, welcome. You are in the right place for help with your K1, and there is lots to be said, and lots that has been said on the subject of head gaskets and top end assembly.
 So hopefully you have been lurking and have done your searches on topics like heavy duty studs, pucks, cam tower studs, retorquing head bolts, frame kits. There is a service bulletin (#42 or #43??) that details the changes that took place between the early and later bikes.
 I'm guessing it is just 11th hour jitters you are having, and the first startup and 50 miles will relieve all that. It would have been a lot better to walk us all through the inside of your motor.

[Henning]

Hello Pablo,
most gasket sets are generic, meaning they can be used with more than one model, so you will have a few o-rings and whatever left over. To my knowledge there are no o-rings between the cylinder block and the head on the K1, so you should be good to go. Kev D mentions a few things to be aware of when installing the head gasket to minimize the risk of leaks - torque the head bolts and wait 24 hours and retorque after backing the bolts off. And use sealant on the pucks (or get some genuine Honda pucks). Lots of advice available on the forum.

[jamesw]

I just wanted to add a quick note.

I dont know if your gasket kit came with the 4 o-rings for the head or not (oil jet & cam bearing oil passage exit)....but be sure to get the right size.

For K0-1 and some early K2....size was 4 x 2mm (3.9 x 1.7 to be exact)

K3 + used 6 x 2mm (5.8 x 1.9 to be exact)

[pablo63]

I bought the bike 4 mnths ago , cosmetically it was an 8 out of ten , brought it home and was going over the bike ,noticed a fair bit of oil around the drive sprocket area so  I removed the chain guard to check the main seal behind the drive sprocket only to discover at some time in it's life the chain had broken and punched a hole in the case , it was about three inches long and an 1/8 " wide at the center , I started the bike and oil was oozing out of this crack ,I decided to clean the area rough it  up with course sand paper and applied some jb-weld ,
I put on 1000 trouble free  miles on the bike , it would start first crank with the kick start and really ran good and it never leaked any oil from the jb-weld . the riding season is now over for me so decided to pull the engine and have this crack properly welded  .This is my first cb 750 engine overhaul , The first problem I encountered was the right side cam cap was broken and the cam end warn down atleast 1/8 ", the next thing was the cam chain tensioner upper wheel had seized and the chain had warn  the wheel and almost half of the inner bearing , the cam chain was rubbing on the metal inner bearing so was also fairly damaged .
  The cases were split , ,  the welding done , new cam chain & tensioner  , used cam blocks ,cam & caps from a donor engine, and the engine re-built .
The only thing that kinda worrying me is the head gasket , in my opinion the quality was not great as the old one that came out had copper rings around the holes for the studs , this one did not and also it is for a later model which uses more o-rings instead of just two for the 1971 model .Just don't want to wrestle this engine into the frame fire it up and find the head gasket leaking oil etc , then have to remove it and re-do all that hard work , so was wandering if anyone has come across this problem and if it would be ok to use the gasket .

[754]

Hope you cleaned out the little jets for the cam oil supply....sounds like one had clogged.
 Where in Canada are you, eh?

[BPellerine]

I would think the gasket would be ok,some with later style head run without the extra orings.bill

[pablo63]

I am in Calgary , the small jets were clear so probably the hole feeding the end cap got plugged , anyhow all changed out with cylinder head , cam blocks ,cam & caps from a donor engine , I see cyclex has a  super gasket top end  re-build kit with what appears to be high quality  stuff and looks like it is specifically for a two o-ring set-up , anyone used this kit ,