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Headgasket for .020 over.


Proven Member
Jun 23, 2009
Strattanville, Pennsylvania
I have done some research and havent been able to get a comfortable answer. I have a .020 motor i will be putting together. I have read that stock bore is 85mm correct? And .020 over would be 85.5mm? STM's Website says that their cometic tri-layer comes in 85.5 STANDARD bore and .020 over 86mm? Extreme PSI doesnt state overbore. I just want to make sure, being that i read .020 over is 85.5mm and STM says its 86mm. Which should i use? If .020 over is 85.5mm, i would get a better seal and sleep better at night knowing its dead on. Just need to get facts straight

Also have to order rings, so i really need to know
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