Cometic MLS vs factory steel shim head gaskets

[Reedogg]

Most agree that Cometic head gaskets seal the combustion chamber really well but they tend to leak coolant. Looking at the gasket I can see why. The Cometic literature says "embossment can not protrude outside of deck or head surface". This is not the case when used on an 8 bolt block. The oil control embossing around the lifter valley due to the upper 3 head bolt holes used for 14 bolts blocks, is not contained by an embossment. Maybe this is the reason they can leak coolant into the oil. It appears to be better suited to 14 bolt applications.

I have a set of .027 Cometics ready to go. I've used Cometics once before without any problems but the high rate of leakage reported by others has me reconsidering. Maybe I got lucky. Cometic also discourages the use of sealant.

The steel shim head gasket used on hot air cars looks like a better solution. It's designed for 8 bolt blocks so there are no embossment alignment issues. Plus they're .020 thick, I'm seeking to maximize compression. Intake alignment would need to be addressed. I know they've been discontinued but they're still cheaper than my Cometics.

Does the steel shim head gasket tolerate cylinder pressure as well? Why aren't more people using this gasket?

 

[No disintegrations]

When head is tightened there is very high clamp load squeezing the gasket. The clamp load is what holds the cylinder pressure. Pinging and or detonation is what lifts the head kills the clamp load and blows out the gasket. Holding the coolant is done with the sealers.
Cometic applied viton to help contain coolant and oil but they need super flat surfaces with correct finish.
I'm sure quite a few people are running the shim type. If they tuned well you'll never hear any complaint really.

 

[earlbrown]

I know for a fact that Cometics with copper spray on a well prepped block/deck will seal well enough to bust pistons without leaking.

 

[Mr.Spool]

I've used Cometics once before without any problems but the high rate of leakage reported by others has me reconsidering.

what you dont hear is how well they work,when put in/prepped properly and tuned right.i will tell you after using all these gaskets the cometics take prolonged hits and seal awesome when your putting the squeeze to the motor.i prefer then on hard running motors with the understanding that when your sealed up top the damage will be below.

 

[Mike Licht]

95% of the coolant leaks are the head studs, put some GM radiator tabs in and it will stop