Topic: Blown head gasket?

[Tugboat]

Bummer.

[Jerry Rxman Griffin aka MuthaF'er]

Blown head gasket is an entirely over used term. The head gasket is probably intact. It's the other things that cause that "leak". Things like warpage or stretched studs that create loose nuts. 

[harisuluv]

I just had to fix this problem on my 550.  Whatever the issue was.  I had a gasket kit from Z1 enterprises and the head gasket started leaking bad.  Took it apart and went Honda OEM this time.  Seems to be holding for now, we'll see.

On the bright side, you can fix it without pulling the motor.

[dave500]

if its not missing and blowing compression out the side or blowing compression between cylinders you might get away with backing off and re-torquing the nuts.

[lrutt]

or cheat like I did with my k8. find some 1/4" cotton rope and stuff in there. I've been running that way for 2 years now and haven't even changed the rope out yet. You can't tell at all unless you're looking for it and it does the trick for minor leaks.

[Fritz]

Hi,
 
 it's likely one of the O rings sealing the oil passage through the cylinder block
 
 I think there are three things that you can do:
 
 1. live with it and/or do the "tampon" trick
 2. Re-tighten the cylinder head nuts - which is not necessarily successful
 3. Change the O-rings which includes a new head gasket, measurement of the sealing faces and possibly resurfacing them.
 If you are to choose step 3, you should change all the top-end gaskets and o-rings
 This route is a little bit risky if you haven't done it before. You could face any of the following problems:
 Broken piston rings
 Bent valves caused by valve cover not installed correctly (a known issue on the CB500, 550 and 650)
 Debris, tools or engine parts fallen into the case
 Oil passage jets lost - they seem to be unobtainable
 Going crazy because the cam chain does not seem to fit over the cam sprocket (cam chain guide installed backwards)
Going crazy because the cam chain tensioner does not seem to fit (the lower part must be inserted into a small groove in the bottom case)
 Going cheap and not have the cylinders and head measured and, if necessary, re-surfaced

 Should I mention that I have the very same leak (although not as bad as yours seems to be) and did not do anything about it for the last 12 months?

Edit: I don't know why - I thought you were talking about a 550 engine, but yours seem to be a 750. In this case forget about the valve cover and cam chain problem - but there seem to be even more rubber seals that could cause the leak.
 
 

[Duanob]

If its a 550, like Fritz says its the o-rings between the head and jugs. They either get dry and cracked from sitting or hot and deformed from a hot engine. Either way the 550 is not a big deal to change it. I did mine twice in one year because the first after market head gasket never fit perfect around the o-rings and sure enough it leaked shortly after installing. The second time I used a Honda OEM gasket and o-rings and sprayed copper seal and so far, so good on the leaks.

Yes you can deal with the leaks but you go through shoes and pants. Tampax only work for so long.

[Tugboat]

It's a '77 CB750K motor y'all..

I have no problem taking it apart and re-doing the top end but it is indeed a motor-off job, and will probably run me about $500 since I'd likely do the $110 big-bore kit while I'm in there plus valve job plus boring/honing/etc. Just don't have the money or time right now.

My buddy had pointed out some particularly dark stains on the leg my jeans last weekend where I'd normally see just a little oil that weeps from the head cover gasket.. but that leak has never been too bad and I just wipe the motor off every few weeks. It doesn't drip on my floor or anything.. When I got to work yesterday I noticed this spot, which is normally clean and dry.

This is a replacement motor for my '76F bike that I got on ebay. It had sat under a tree (on a bike, with headers & carbs/airbox still hooked up) for years in upstate NY before being sold to me. I literally just gave it a tuneup, threw it on my bike and have now put a couple thousand miles on it with no real problems; but I guess I really only bought myself some time, as opposed to having bought a permanent solution. I haven't done a compression test yet, but I'm betting that #1 is low.