Question about Cometic Gaskets

[eckoxl]

"ATTN: If you are using 3500 heads on a 3400 block, you must use a gasket bore of 3.720" or larger to clear the combustion chamber."

I am using 3500 heads on a 3400 block and my question is what option do I select for the Bore & Thickness? I am just looking for the stock size; not looking to change compression or anything.

[robertisaar]

according to the compression calc, stock head gasket bore is 3.75" and compressed thickness is .06"...

for a 3400, anyways.

[3400-95-Modified]

You buy what I just did... stock bore 3500 gaskets, those from Cometic are 3.72" And then you pick the thickness you want... Stock compressed is .060.

Right from the 3500 listing for the gaskets

Gasket thickness of .060" stock is default, with the option for thinner or thicker based on your specific quench/compression needs. 3.720" is the default MLS gasket bore size for the 3500 engine. A smaller gasket bore will not clear the 3500 combustion chamber. The stock GM gaskets were 3.800". if you are boring the block, please select the head gasket equivalent to the piston overbore size.

Note that stock GM 3500 head gaskets were 3.8" bore, and stock GM 3400 head gaskets were 3.75, this is why you can use a 3400 GM gasket with 3500 heads... its over the 3.72 min size. Where a stock 3400 MLS gasket is only 3.64" That is too small for a 3500 head.

You could buy the 3400 head gaskets with a .010 overbore, but that would put you at 3.74.

I went with the size recommended for a stock bore 3500 which is 3.72 since I'm assuming that will be spot on as far as hugging the 3500 combustion chamber.

[eckoxl]

All I want to know is what option to select for bore and thickness.

[mfuller]

3.720" bore (i.e. "Standard"), .060" thickness.

[SappySE107]

I am adding the option for stock dimensions. I think you want 3.750" bore and .060 thickness to be the exact same as a stock 3400, correct? While this will be slightly less efficient to having a gasket bore near the cylinder, it will allow you to bore the block and use the same gaskets.

[geldartb]

I am adding the option for stock dimensions. I think you want 3.750" bore and .060 thickness to be the exact same as a stock 3400, correct? While this will be slightly less efficient to having a gasket bore near the cylinder, it will allow you to bore the block and use the same gaskets.

ok to achieve the 3.75 i would pick the .030 gaskets right.

[SappySE107]

yes, or you can now go to the 3400 listing and select the Stock (3.750") option.

[geldartb]

i did the math just wanted to make sure i was correct.

didnt see the option in the 3400 section. i just looked at the 3500 ones.

keep making things easy for us Ben good job. ill be hitting you up for some in a few weeks.

[eckoxl]

So I need to order Bore: Standard & Thickness: .060. Correct?

[geldartb]

choose the stock option in that drop down menu its down the bottom of listed specs and yes .060 is the one you want.

im thinking standard will get you the standard size gaskets which is smaller diam. am i correct Ben

[eckoxl]

3.720" bore (i.e. "Standard"), .060" thickness.

confused. lol.

[SappySE107]

I am just looking for the stock size; not looking to change compression or anything.

Then select STOCK and .060.

[eckoxl]

Thank you and ordered.