Cometic MLS head gasket misbuilt?

[Jim Comet]

Hey guys, I opened my Cometic MLS head gaskets this afternoon to install them and believe they may have been miss-built. They are supposed to have 4.165 bores. While part of the bores are 4.165 they are oblong and open out to 4.3" and barely have any raised lip for sealing. I am going to call Cometic on Monday and check. Just wondering if any of you have seen something like this before or not. I have had 2 previous sets of these and they had round 4.165 bores. Thanks for your thoughts. Jim

[thatdarncat]

Someone on one of the FE Facebook pages just a couple weeks ago posted similar mis-formed Cometic FE heads gaskets. The consensus of the knowledgeable seemed to be they are indeed “wrong”. No idea what’s going on at Cometic, but you may not be alone.

[GerryP]

Covid gaskets.  There are a number of threads of goofy Cometics.  Water holes not lining up, oblong bores and all that.

[Jim Comet]

I actually laid the new gasket on the head and it shrouds the exhaust valve by 1/6 of on inch or more. I laid the old Cometic gasket on the head and it does not shroud the valve. I'll let you know what Cometic says on Monday. Jim

[Jim Comet]

I talked to Cometic and this is their standard design for the FE gaskets. I believe the exhaust chamber has been laid back on my ProPort heads which may be the cause of the overhang. My old round chamber design 4.165 Cometics did not interfere so I ordered a new set of round 4.170 MLS gaskets. I'll know in a week. Jim

[pbf777]

        Yes, Cometic's "standard" cylinder opening profile is that which presents the oblong shape intended for chamber reliefs (O.E.M. stock heads), but "all-round" gaskets, along with bore dimension options, can be hand if you stipulate such at the time of ordering.   

        Scott.

[Jim Comet]

I got the new Cometic 4.170 gaskets and they clear the cylinder but still shroud the chamber when laid on the head. Would you consider using a fine die grinder on the head gasket to profile it to the cylinder head chamber shape. It only interferes at the 2-3 and 9-10 O'clock areas. The gasket does clear the whole cylinder on the block. Wondering if the gasket protruding into the valve area but clamped by the head on the cylinder would pose a hot spot potential or burn issue? Jim

[pbf777]

         You do not want the gasket to be directly exposed to the combustion events of the combustion chamber; generally a minimum of say .030"-.060" set-back from the exposure area is best to shield the gasket from the direct resultant heat and pressure effects of combustion.     

         I would doubt that the gaskets' embossment positioning would permit "trimming" of the gaskets profile in this critical area and still remain viable in its' sealing responsibilities; but look, maybe..................?   

         Scott.

[Jb427]

         You do not want the gasket to be directly exposed to the combustion events of the combustion chamber; generally a minimum of say .030"-.060" set-back from the exposure area is best to shield the gasket from the direct resultant heat and pressure effects of combustion.     

         I would doubt that the gaskets' embossment positioning would permit "trimming" of the gaskets profile in this critical area and still remain viable in its' sealing responsibilities; but look, maybe..................?   

         Scott.

This caught me out too when i was buying my cometics my finished bore size was 4.250 and my pistons came out 0.005 down the hole i ended up with 4.300 and 0.036 thick cometic. after returning my first set that was too small bore size.
I am no expert but I think you would want like pbf777 said 0.030 - 0.060 over what ever your finished bore size is. Maybe send a photo of that too cometic see what they say about the chamber overhang?