Head Gasket for 40 Over

DeLayne_7287

DeLayne_7287

New member
First off, Happy New Year!

We have been in the process of rebuilding a 2004 5.9 (machined and 40 over) and I ordered a 40 over engine rebuild kit that came with the 40 over pistons, etc. along with the gaskets. The head gaskets that came with the kit are the standard size head gasket, though.

Cummins says that they do have a 40 over gasket but it is hard to get/find and is much more expensive. They gave me the part number and nothing comes up online for it.

I figured that once you select 40 over pistons when you order online, the kit would automatically come with a head gasket for 40 over, but it doesn't or at least this one doesn't. We put the gasket on to see how it sat but some spots obviously slightly cover the cylinders, which seems that it won't allow it to make a good seal and won't last long if I go with it.

So, what head gasket are yall using when yall have a block that's punched out 40 over? I see that they have 20 over gaskets but can't find them for 40. Any suggestions or explanations would be great! Thank you!
 
Oversize head gaskets are referring to thickness, not bore diameter. They were designed to be used when piston protrusion exceeds spec.
 
I've noticed that they have different thickness options (1.10, 1.20, 1.28, 1.55), but some also have a bigger bore, too, which is why I'm confused about the kit not coming with one of those.

The bigger bore sizes I'm coming across so far on head-gaskets are 107.4mm and 104.14mm by Mahle and Cometic.
 
Cummins does make an overbore head gasket in two thicknesses. They are ridiculously expensive. We have never used them when we build 020 or 040 engines.
3966343 thin overbore gaskets ISB CR 420.00
3966342 Thick Overbore 450.00
 
Last edited:
After several calls being made, the regular gaskets are obviously sometimes used by SOME people BUT, it is "not the right way to do it on an over-bored block" so, they are in the process of sending the right gaskets from Mahle.

Thank yall for the input!
 
You must log in or register to reply here.
Back
Top