Cometic MLS head gasket and Hylomar

[Hap]

Want opinions on using Hylomar M (blue) with Cometic MLS head gaskets.
Back when Cometic MLS gaskets were rolling out, their rep recommended coating both sides of the gasket with Hylomar M spray.
Is this still necessary or better for sealing purpose?

Current build is SBC G1, iron block decked and finished for MLS and new aluminum heads.

Appreciate all feedback.

[Frankshaft]

Want opinions on using Hylomar M (blue) with Cometic MLS head gaskets.
Back when Cometic MLS gaskets were rolling out, their rep recommended coating both sides of the gasket with Hylomar M spray.
Is this still necessary or better for sealing purpose?

Current build is SBC G1, iron block decked and finished for MLS and new aluminum heads.

Appreciate all feedback.

If the finish is good, then from new, I usually don't put anything on them, other than where the oil drains from the heads, on both sides. On a reuse, I will either use a light coat of hylomar around the water ports on both Block and head side. Or even silicone, I have also sprayed them with copper coat. Never had a water leak. I have used cometic gaskets as many as 5 times, with no issues, with the exception of high compression big block and small block Ford's.

[cjperformance]

My preference is copper spray or non hardening aviation gasket like permatex/loctite. Hylomar also.
Im not a great fan of any silicone/rtv type product on a headgasket as the possibility of the bond between gasket and block/head breaking down is too high.

[Newold1]

If the block deck and head surfaces are straight, properly decked and at a recommended RA then just clean the surfaces with alcohol and a lint free cloth, install the Cometics and torque- You're done! Been doing sbc' LS's and BBc's and have never had a leaker. The Cometics are coated on both side sealing surfaces with Viton and that is the sealing secret with Cometics MLS gaskets.

[cjperformance]

Yes, frank and newold, if new no sealer. I was referring to franks reuse of mls type.

[hondo383]

Copper spray for re using here too....skim of.silicone only on the thin part of the deck heading up to the China wall both sides of gasket. Even if your heads are new make sure they get surfaced properly!

[Alan Roehrich]

As stated up thread, I get 5-6 uses out of a set of Cometic gaskets by using Permatex spray copper after the first use. Up to 13.5:1, on big and small block Chevy engines. And honestly, nothing special about the surface,the machining is done on an SV 85B, sharp and well adjusted, with variable traverse. Cast iron and aluminum.

[groberts101]

If the gaskets are fresh and viton coatings 100% intact.. no hylomar is warranted. If they have been used and recycled a few times causing the viton coating to flake off anywhere near water passages?.. thin hylomar around water passages will add cheap insurance to prevent leaks.

[peejay]

have used cometic gaskets as many as 5 times, with no issues, with the exception of high compression big block and small block Ford's.

Could you expand on that a bit, please? Any particular block or head (OE/aftermarket, iron/aluminum?)

I have had some SBFs where I had one hell of a time trying to get the head gaskets to seal. Also interested in your BBF experiences because I dabble with those every now and then.

[Cubic_Cleveland]

I don’t use anything on new mls gaskets either. That’s what the black viton coating is for.

On a similar note, what are people using on copper gaskets these days? I used to use the non hardening permatex aviation, but it’s been so long since I’ve used them wonder if anything’s changed? Especially around oil feed passages...

[cjperformance]

I don’t use anything on new mls gaskets either. That’s what the black viton coating is for.

On a similar note, what are people using on copper gaskets these days? I used to use the non hardening permatex aviation, but it’s been so long since I’ve used them wonder if anything’s changed? Especially around oil feed passages...

On copper gaskets, i use copper spray or avaition. Cant go wrong with either, both stand up to heat cycles and retorque

[Hap]

Appreciate the replies and opinions.
Will go with no sealer for this build; being the head and block surfaces are fresh machined, and engine is relatively low HP (-500) and low compression.

[ctk30]

What happens to a Cometic if the surface is oily?

[engineguyBill]

MLS head gaskets should be installed dry (no goop) on clean, dry, straight head/block surfaces. The use of any sealant or other goop will very likely lead to gasket failure.

[Newold1]

No head gaskets should be installed on oily decks or surfaces with sealers, even Cometics!