cometic head gaskets


New Member
Jan 30, 2005
blew my stock head gaskets
looking to use the cometic ones.... has anyone used them before?
If so what do you guys think?
Do a search, you will find a lot of info.

I think in general, you will find that:
a) heads and deck must be very flat
b) they will probally leak at first (water)
c) use the gm stop leak pellets
d) thet are reusable
I have them on my car and so far they are great but there were some very specific instructions that came with them I bought them. Cometic claimed that the block and head surfaces needed to be 50RA or smoother for proper sealing. When I had my motor built the machine shop's surfacing equipment wasn't capable of acheiving 50RA so the head and block surface had to be "lapped" to get there. According to the machine shop normal surfacing equipment would produce a surface of about 70RA(I think, that was a year and half ago) I installed mine dry as suggested by Cometic but I have heard of others using copper coat or something similar when replacing stockers and not having the 50RA surfaces.
Do not put them on a 120k mile original block and aluminum heads like I did! They leaked like crazy. Well the passenger side was OK but the driver side was crazy. You could see my engine compartment smoking so bad because water was leaking on the header. My block was not flat at all. Went back to the Felpro 9441PT's until I recently split my block. No leaks. Only run cometics if both surfaces are 100% flat and many people spray hylomar (copper spray) on all 4 layers of the gasket to help seal.
I have been using cometics on a 60k shortblock with aluminum GN1's for two years with no leaks or problems. I sprayed them down with copper and used a few GM seal tabs during the install.
Let's see the stockers lasted about 20 years on the car and you want to use Cometics because ?......... :confused:
how about if you lift (blow) one of them- they dont go through your whole block which you would have to then pull to get all the parts out of?
Yeah I guess 20 years isn't reliable enough for most folks. :p

I'd go with a "better" gasket. ;)

Rumor has it IF you get them installed and not leaking they don't lift much at all, so you end up going through the motor anyway looking for crank and piston parts when the KR hits. :eek: :(

One would think a list of your intended buildup would be in order, for just replacing your factory headgaskets in the car without being able to flatten the block, stockers just might last as long as the rest of the motor. :cool:

I run cometics with GN1 heads and 70RA on the block with zero issues. Earlier this year I blew an RJC gasket. I have lots of miles on the cometic, very happy!! Installed with hytach.