305 Head Gasket-What Caused This?

jcspc · Post by **jcspc** » Sun Aug 30, 2009 3:24 pm

Yep, my machinist checked them out when I did the top end. Valve job, sleeve, bore both cylinders to spec. The gasket seems suspect to me.

LOUD MOUSE · Post by **LOUD MOUSE** » Sun Aug 30, 2009 6:24 pm

I see that the gasket failed (pic of the compressed "O" ring?) and I will continue to use a "O" ring with a little larger thickness that will compress and not expand enough to push on the gasket at that point.
Why ya may ask.
Well the ones I use don't compress enough to PUSH to the outside of the space that's there at the area to the hole in the gasket when in place. ............lm

jcspc wrote:Yep, my machinist checked them out when I did the top end. Valve job, sleeve, bore both cylinders to spec. The gasket seems suspect to me.

jcspc · Post by **jcspc** » Mon Aug 31, 2009 6:04 pm

My assumption is that the o rings were too big so that when the head was compressed down, the o rings filled too much space and forced the gasket apart. I used the same size o ring on both sides so therefore both sides of the gasket blew out and produced the leak.
As far as the gasket goes, I guess the gasket was at least an ok quality. It came out of a DK Gasket set which I know others have used them with success. Now... how about those o rings? What size do you use and where do they come from. Honda Dealer? My local dealer doesn't want to get me a screw w/o a part number...

davomoto · Post by **davomoto** » Mon Aug 31, 2009 8:01 pm

They usually come in top end gasket sets, or search an online microfische for part #.

davomoto

jcspc · Post by **jcspc** » Mon Aug 31, 2009 8:51 pm

Yeah, but what about the oversize ones LM talks about. Maybe just the standard with the Hondabond stuff is all that is needed. I mean, how about you. Do you use the standard stuff and Hondabond and have no troubles? Am I just making too big a deal of all this?

jensen · Post by **jensen** » Tue Sep 01, 2009 12:27 am

Hi,

Loud mouse, could you give the sizes of the o-rings you use ? (outer diameter and thicknes)
And if possible, the material they're made off ?

Untill now I never had any problem with the original o rings (and I never use bond in these area's either), but maybe it's different for a CB77 than a CB72 ? (I don't think so, but I don't have the experience with CB77 head).

I myself make sure that the head and cilinder are flat within 0.01 - 0.02 mm, and torque the bolts down with a torque wrench to the specified torque. After a few hunderd miles, I torque them down again with the specified torque, like I said I never had any trouble like this.

jensen

davomoto · Post by **davomoto** » Tue Sep 01, 2009 1:46 pm

CB72 and 77 seal the same way. I like to use the Hondabond around the o-rings to seal the gap that Ed descibes. He , appearently uses slightly oversize o-rings. I have yet to have one leak using my method, so I'm sticking with it!

davomoto