Question 1. What is the tolerance for head gasket thickness

question 2 . Does it make sense to buy slightly thicker head gasket for rebuilding head . Some cases head needs to machined . When i say thicker i mean .50 to 1 mm thicker ?

 

I just had my head rebuilt / resurfaced by RRE. They chose the stock OEM head gasket

Dont think you can go w/a thicker gasket w/out messing up other things like compression ratio

Welcome aboard by the way

 

From what I've read, thicker head gaskets causes problems by creating a pocket where the thicker head gasket separates the head and block. I can't remember exactly what it was but if you look at the head, there are flat spots past the intake and exhaust valves (circled in red).

 

If you get your head milled each time you remove your head, eventually, your valve clearance won't be sufficient and pistons can make contact before valves fully close. I think the best way to fix that is to install your valves deeper into the head by cutting deeper valve seats. But that requires each valve to be shimmed under your valve springs to lift the valves. There will come a point where it is cheaper to buy a new core.
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Thank you very much guys for the info. I am using a composite style head gasket (aftermarket) graphite with steel core and it is about 0.50 mm / 0.019" thicker than OEM . I think thicker gasket will reduce the compression ratio by a small fraction, probably only by .1 or .2 my main concern is risk of gasket failure. What is the acceptable tolerance for head gasket thickness. Should I use it or stick to OEM.

Thank You
Lokesh

 

Is there such a thing as tolerance for a gasket? Tolerances that I've seen are for metal surfaces. My gut tells me the thicker the head gasket, these easier it is for leakage from lifting. Hopefully a guru will pop in soon for you.
Yes, compression will lower but the extra void would be tough for combustion to burn.

 

Of course I can't find the article, but I just remembered a little more about why we should avoid thicker head gaskets. Pistons usually have slight raised lip around perimeter to minimize combustion from reaching the rings. With thicker head gaskets, that increases the risk that combustion can reach the rings and start cooking it.

 

Also, by lowering compression with thicker head gaskets, the extra volume in that red area would burn late since that is much farther from the spark. It wouldn't make as much power than if you shave the dome area. I can understand using thicker head gaskets to add clearance for valve to piston, but the trade off is efficiency and higher risk of head lift under high boost.

 

Gasket thickness is only a concern for when the block is decked in order to maintain the squish distance.

The small compression ratio change from milling the head can be accounted for with the tune.

Running a thicker gasket is in absolutely no way harmful. I have a 4g63 running around with a .060" thick head gasket in it, no issues at all. Just what as needed since we used shelf pistons (couldn't adjust pin height) and it was the second time the block was surfaced.

That being said, I would get an OEM gasket. If you're for some reason worried, you can run a 9 gasket on your 8, they are .011" thicker. If you have 9, just run the 9 gasket. It'll be fine.

 

0.011" comes out to about 0.28mm.