Cometic MLS head gasket and Hylomar

[groberts101]

Maybe that's true but they also say they're not reusable as well. Sometimes the guys that do things and repeatedly get away with them have figured a few things out that others have not taken chances on. Seen more than a dozen motors including my own use cometics and hylomar upwards of 13:1 with no signs of failure.

If there is one thing I have noticed on teardown when using hylomar on these gaskets is that it reduces fretting tendencies due to disimilar expansion rates and movement(aluminum heads on iron block) of the viton coatings themselves. The smoother the block and head finishes the less tendency for viton coating deterioration but hylomar sure don't seem to hurt matters on rougher finishes.

New gaskets go on dry.. each use after that gets small application of hylomar to compensate for viton coating degradation and the stamped embossements reduction in height caused by the heat and load cycles.

[user-17438]

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.

Same here

[ctk30]

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

Just hypothetical

[steve cowan]

hey guys,
whats the best cleaner to use on the MLS gasket that is being re-used
thinners,grease and wax remover (prepsol)
also are you required to re-torque a cylinder head after a couple of heat cycles when re-using a MLS head gskt.
i am thinking of re-using a pair but was a bit apprehensive but seriously considering it now after this thread,thanks for any feedback

[cjperformance]

Hey Steve, yes prepsol(or equiv) is great and does not eat any left over coating. Depending on the type, thinners can affect the coating so take care.
Make sure all trace of the prepsol has evaporated, you can use a hot air gun for some warmth if you need them straight away.
I dont retorque them, i use properly lubed(or sealer if reqd) bolts/studs, clean threads etc. I have marked the bolts after final torque and gone thru both a cold and hot retorque just out of interest and it proved a waste of time and has potential to upset sealer if used.

[steve cowan]

Hey Steve, yes prepsol(or equiv) is great and does not eat any left over coating. Depending on the type, thinners can affect the coating so take care.
Make sure all trace of the prepsol has evaporated, you can use a hot air gun for some warmth if you need them straight away.
I dont retorque them, i use properly lubed(or sealer if reqd) bolts/studs, clean threads etc. I have marked the bolts after final torque and gone thru both a cold and hot retorque just out of interest and it proved a waste of time and has potential to upset sealer if used.

good info
thanks Craig

[englertracing]

I have put the mls on dry, and with hylomar.
I don't think hylomar hurts anything.
I think the stuff is really neat.

[steve cowan]

is there a risk of leakage in the following??
same short block with same used MLS head gskt
removed aluminum dart heads 215cc
replacing with cast iron dart heads 180cc
i would think the water passages might not line up correctly and possibly cause a problem.
i have a new set of MLS head gaskets i would use on the cast iron heads and keep the other used gaskets for the aluminum heads on that short motor.
so my question is - do you have to keep matched block,head and head gaskets together?? i would say YES but that that is my assumption.
thanks for any information

[groberts101]

is there a risk of leakage in the following??
same short block with same used MLS head gskt
removed aluminum dart heads 215cc
replacing with cast iron dart heads 180cc
i would think the water passages might not line up correctly and possibly cause a problem.
i have a new set of MLS head gaskets i would use on the cast iron heads and keep the other used gaskets for the aluminum heads on that short motor.
so my question is - do you have to keep matched block,head and head gaskets together?? i would say YES but that that is my assumption.
thanks for any information

Assuming the gaskets viton coatings are still relatively intact why would it matter? You're saying both those heads differ from one anotyer in oem water passage locations?

[cjperformance]

I think I know what Steve means about coolant passages, im thinking that the coolant holes are not in the wrong or different positions but maybe just differ in shape and or size as is the case with heads for the same engine but made by a different manufacturer, correct Steve?
If this is the case in reality you may not have a sealing problem but personally I would keep the mls gasket common to the cylinder head you use it for. 'If'the differing shape coolant holes compress/load the gasket and coating differently then there 'could' be a higher chance of seepage. So by all meand reuse the mls but have a gasket per cylinder head, then you will be safe swapping those heads over on the same short block.

[groberts101]

I think I know what Steve means about coolant passages, im thinking that the coolant holes are not in the wrong or different positions but maybe just differ in shape and or size as is the case with heads for the same engine but made by a different manufacturer, correct Steve?
If this is the case in reality you may not have a sealing problem but personally I would keep the mls gasket common to the cylinder head you use it for. 'If'the differing shape coolant holes compress/load the gasket and coating differently then there 'could' be a higher chance of seepage. So by all meand reuse the mls but have a gasket per cylinder head, then you will be safe swapping those heads over on the same short block.

Unless the embossed portion of the gaskets outer layers has been loaded in an uneven manner, such as overhanging into water passages and caused distortion of the embossements?.. shouldn't matter one bit. I used to be afraid of leaking or popping these things early on but they're far tougher and more resilient than some may realize.

On the other side of the coin.. if you already have new parts in hand?.. why push boundaries when it's not necessary. As CJ says.. start with fresh parts on the swap and just keep the old gaskets paired up with the old heads.

[steve cowan]

I think I know what Steve means about coolant passages, im thinking that the coolant holes are not in the wrong or different positions but maybe just differ in shape and or size as is the case with heads for the same engine but made by a different manufacturer, correct Steve?
If this is the case in reality you may not have a sealing problem but personally I would keep the mls gasket common to the cylinder head you use it for. 'If'the differing shape coolant holes compress/load the gasket and coating differently then there 'could' be a higher chance of seepage. So by all meand reuse the mls but have a gasket per cylinder head, then you will be safe swapping those heads over on the same short block.

Craig,
You are correct in my assumption, I figured the water passages in the heads might leak if they don't line up and I am confident the passages would be slightly different even from the same manufacture.

I think I know what Steve means about coolant passages, im thinking that the coolant holes are not in the wrong or different positions but maybe just differ in shape and or size as is the case with heads for the same engine but made by a different manufacturer, correct Steve?
If this is the case in reality you may not have a sealing problem but personally I would keep the mls gasket common to the cylinder head you use it for. 'If'the differing shape coolant holes compress/load the gasket and coating differently then there 'could' be a higher chance of seepage. So by all meand reuse the mls but have a gasket per cylinder head, then you will be safe swapping those heads over on the same short block.

Unless the embossed portion of the gaskets outer layers has been loaded in an uneven manner, such as overhanging into water passages and caused distortion of the embossements?.. shouldn't matter one bit. I used to be afraid of leaking or popping these things early on but they're far tougher and more resilient than some may realize.

On the other side of the coin.. if you already have new parts in hand?.. why push boundaries when it's not necessary. As CJ says.. start with fresh parts on the swap and just keep the old gaskets paired up with the old heads.

Thanks GR for your reply, no point in causing unnecessary problems, new gaskets are the ticket

[mk e]

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

Aviation dealer as in the black goo they have been selling forever? I used to love that stuff as cheap insurance but as I've gotten older I started to find things I put it on years ago it has turned to a tan colored dust over the years......10-15 years maybe? Aviation and race engines and require tear down so it's never an issue for them, but I no longer put that stuff on anything I'm not planning to tear apart again anytime soon....518 (anaerobic) is my new go to.

[cjperformance]

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

Aviation dealer as in the black goo they have been selling forever? I used to love that stuff as cheap insurance but as I've gotten older I started to find things I put it on years ago it has turned to a tan colored dust over the years......10-15 years maybe? Aviation and race engines and require tear down so it's never an issue for them, but I no longer put that stuff on anything I'm not planning to tear apart again anytime soon....518 (anaerobic) is my new go to.

Mark, yes correct on the aviation over the long time span, it does eventually degrade and turn to that dusty crust for sure.
I've never tried 518 on a head gasket, that said I'm sure it would be perfectly its very good stuff.
I wonder how that will go long term, 10/15 years?

[mk e]

Mark, yes correct on the aviation over the long time span, it does eventually degrade and turn to that dusty crust for sure.
I've never tried 518 on a head gasket, that said I'm sure it would be perfectly its very good stuff.
I wonder how that will go long term, 10/15 years?

I've not tried 518 on a head gasket....I've been scared about the film thickness. The aviation sealer torques out really thin but 518....a few thou is about as thin as it gets I think. I use it on just about everything else and have been using it since the mid 90s....everything I've ever torn apart has looked good.....it does get a little brown where it was hot but still seemed to be flexible and sealed.