Tolerance for head gasket

[Susan Lybolt]

New rebuilt over heated. I have .02 on the head and .02 also on the block. Do I need to machine the head before refitting the head gasket?

 

[Legal Bill]

I assume you measured this with a straight edge and a feeler gauge? .02 is 20 thousandths. What I am reading is that combined you have a 40 thousandths gap between head and block. Is that correct? I'm pretty sure the head gasket cannot tolerate a .02 gap. I'm positive it cannot tolerate a .04 gap.

 

[Keoke]

0.02 Hmmm
Weren't the surfaces machined as part of the rebuild ??

 

[Susan Lybolt]

They were good until I used the wrong radiator cap. Short stem, lost antifreeze. Temp off the gage. You could say I red lined it.

 

[John Turney]

Well, at least you didn't flat line it. I think you need to resurface.

 

[Keoke]

They were good until I used the wrong radiator cap. Short stem, lost antifreeze. Temp off the gage. You could say I red lined it.

Well the simplest thing to do is resurface the head.

 

[CraigC]

Susan can you confirm that both the block and head are 0.020" out of flat or did you mean 0.002" ?
At 0.002" you cou​ld assemble as is.
If you really are 0.020" out, the block will require decking at a minimum. More importantly it should be checked in EVERY dimension to make sure cylinders aren't out of round and the block is not twisted.
If you severely overheated, good chance your rings are done. Reusing them may result in excessive oil consumption and/or blowby.
I would not recommend surfacing the head to eliminate 0.020" of bowing. You will end up with additional problems such as differences in combustion chamber volume that will raise compression in cylinders where the most material is removed. There are specialist companies that "might" be able to straighten that successfully.
Do it correctly now. You will be better off in the long run.

 

[Susan Lybolt]

The head and block were measured with a levelometer and feeler gauge. They were .002 in different areas of the head and block. not .02.

 

[Keoke]

The head and block were measured with a levelometer and feeler gauge. They were .002 in different areas of the head and block. not .02.

I figured that was the case as at 40 thousandths there would have been no argument.
Still the simplest thing to do is resurface the head.

 

[steveg]

This site discusses tolerances:
https://www.aa1car.com/library/ic697.htm

.002" sounds like you could probably just install a new head gasket.

 

[vette]

Susan, get a hold of some of the companies that actually make head gaskets. There are many American performance car companies that might have a pattern for the Healey. They make many types of gaskets that can compensate for irregularities. I don't think .002" is too much to compensate for. Dave.