Topic: What exactly did PO do?

[Patrick]

So I started tearing down the engine in my K0 project. The top end came apart surprising easily, so I already knew before I pulled off the head that the PO had been in here before. What I found were very good condition ART pistons and good condition bores. I had them honed and they were in spec.

The pistons, however, measure 64mm, and I understand stock is 62mm, right? I think I can put the top end back together, since it looks like someone rebuilt the bike and then parked it with almost no miles on it.

My problem is the head gasket. The holes on the head gasket I pulled off were 62mm, so I figured the PO used a stock head gasket with a big bore. Can this be done? If not, where do I find a head gasket with 64mm holes?

Or do I need to put the project aside until I can afford a proper 65mm big bore kit and cylinder bore.

As always, all suggestions are appreciated.

Patrick

[Sam Green Racing]

Hi Patrick, I'm not sure what pistons you have there but the stock bore size it 61mm.

Honda normally only go up to 1mm in over bore sizes so the 62mm gasket would be OK for standard and overbored pistons only.

Sam.

[Patrick]

Thanks, Sam. Any idea where I could find a head gasket with 64mm holes?

Thanks.

[Sam Green Racing]

You could try www.cometic.com

Sam.

[Patrick]

By the way, any idea what kind of piston this is? They have ART on the side, so I believe the pistons are actual Honda parts, but it measures 64mm. I read on the Satanic Mechanic site that Yoshimura makes an 812 big bore kit. Anybody know who sells these big bore kits? they might sell just the gasket.

http://i130.photobucket.com/albums/p247/wordguy11111/Piston.jpg

Patrick

[Sam Green Racing]

Patrick, 64mm would be the 810 kit (810.7868cc)

Sam.

[Patrick]

I calculated that too, Sam. But I figured when you're talking about putting a big bore in a 750cc motor that is really a 736, you just might fudge the numbers on the other end too. Plus, a 1 cc difference over four holes seems like it might be within tolerance for an 812 gasket. 

Patrick

[Sam Green Racing]

I would go for the Cometic 65mm gasket, it's only .5 more of a mm all round, can't see it causing hot spots or anything.

Sam.

[Patrick]

I looked at their website and it says the 65 is also good for an 811 kit (another volume enters the fray). CycleXchange has a 65.5 for about half the price. I'm wondering how much tolerance I have. I am, however, fortunate that the PO didn't look harder for the right gasket. It saved the engine a lot of time actually running, saving the parts a whole lot of wear.

Patrick

[eurban]

I have a couple of NOS Yosh head gaskets which if memory serves are for the 810 cc range. Let me know if you are at all interested and I will dig em out and inspect more closely. . . . .Ok so I found the gaskets and they are Pops Yoshimura Racing Parts model 41801 and the metal rings measure out at 65mm in diameter.  If I recall correctly, this is a bit smaller in diameter than the Cometic gasket that came with my Wiseco 836 kit.  I don't know off hand how much larger the gasket ring should be than the cylinder bore.