Topic: CB750 1mm overbore Gasket?

[Seb656]

I have a 1976 CB750A with a 1mm overbore sitting in my garage (that would mean its 62mm bore). I went through and changed out the gaskets on it and used a stock head gasket. The bike ran for about 15 miles then the head gasket failed. I am not sure to chalk it up to a bad gasket, poor heat cycling of the gasket, or the wrong gasket. The gasket remained intact on cylinders 3 and 4. The metal o rings that surround the jug create a slight lip over the jug and seem to have overheated and been destroyed on cylinders 1 and 2. Does anyone know if I should be using the stock gasket with the 61mm rings or an aftermarket gasket?  I seem to only be able to find a 61mm and 65mm. The 65mm would obviously be overly large nut it wouldn't leave the metal rings inside the combustion chamber instead there would be a slight gap.

I am really at whits end with this issue. Any experience or help that could be offered would be much appreciated

Thanks,
Seb656

[MCRider]

Generally speaking, the 1mm over is the high end of stock overbores and the stock head gasket is proper to use. The bit of ring that hangs in the cylinder is not material. It should not have caused you that problem. That's my opinion with some experience. Others may differ and we may learn something.


I've known people who have used a stock gasket with an 836 kit and lived to tell about it (ahem).

If you have to have it, I think Cometic will make the gasket any size you want.

http://www.cometic.com/custom.aspx

[wrenchmuch]

Was it an aftermarket gasket ? If so it might be a fitment issue that an oem gasket might solve . I'm thinking of using a 1 mm kit in my K4 re build . Please post back your findings .
Thanks
Mike

[HondaMan]

Like they said above...

What brand of gasket was it? Usually, the stock size gasket is good to the 4th overbore, just fills in with carbon around the small perimeter void.