Blowing head gaskets?

[MMor101]

On my big bore I keep blowing head gaskets. I'm using a 61x cylinder with a 64u(760?) head with a cometic gasket. Both surfaces seem flat. Last season I bored the top end from 85mm to 85.5mm. Does anything have to be done to the head after the cylinders are bored? I'll get a pic up of the head gasket.

 

[Matt_E]

You are using an oversized head gasket, right?

 

[MMor101]

Yes, the Cometic 86mm head gasket for the 760's.

 

[Matt_E]

Make sure the deck of the cylinder and the head are plane.

 

[MMor101]

I checked that too. I thought the sleeves had dropped. I just used a metal ruler straight edge. Is there a better way? Would an aftermarket head remedy my problem? The plug that didn't get water on it was a nice coffee color. Would an air leak cause this?

 

[Matt_E]

An airleak is unlikely to be responsible for this.
An aftermarket head MIGHT fix the problem if your cylinder is indeed flat (and the head is not flat).
However, O=Ringed heads (Aftermarket) are less forgiving for flatness than gasketed heads.