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Thread: Cometic MLS head gasket fitting method

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    Cometic MLS head gasket fitting method

    Hopefully someone can help with the process of fitting an MLS head gasket - I'm not usually a fan of them as feedback I've had about them is they are difficult to get a decent seal - but the engine needs one of these due to bore size.

    Is the recommended method (new gasket, not used) to use oil on the faces, Hylomar blue, or dry fitting?

    The engine already has a Cometic MLS on it, I'm just replacing as the engine is coming to pieces and as it hasn't had any issues I'm confident the head/block has the correct RA finish.

    Are there any other tips or tricks?

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    Re: Cometic MLS head gasket fitting method

    i fit they dry and have never had any issues, but that has always been with freshly skimmed block and head. it might be more critical if the gasket is reused, personally i dont reuse them id rather pay for a new gasket than risk a failure, i just dont see how they can be as good a second time round.

    ondy says use blue hylomar to avoid weepage of the waterways. which is probably good advise, i dont think he does anything simply for the sake of it. hylomar can be bought in aerosol form which is good for getting a thin light application.

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    Re: Cometic MLS head gasket fitting method

    i've fit them dry but some of the american forums use copper gasket spray. apparently they can be re-used. time will tell as i have re used mine for the first time although the car did not actually run and cometic say this should be no problem

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    Re: Cometic MLS head gasket fitting method

    I was advised by a well reputed competition engine builder to use a a thin coating of Welseal on a MLS gasket.

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    Re: Cometic MLS head gasket fitting method

    Quote Originally Posted by Graham View Post
    i fit they dry and have never had any issues, but that has always been with freshly skimmed block and head. it might be more critical if the gasket is reused, personally i dont reuse them id rather pay for a new gasket than risk a failure, i just dont see how they can be as good a second time round.

    ondy says use blue hylomar to avoid weepage of the waterways. which is probably good advise, i dont think he does anything simply for the sake of it. hylomar can be bought in aerosol form which is good for getting a thin light application.
    Nice one, thank you Graham. And you're right : Onyd is very on the ball (as you are too!)

    Quote Originally Posted by fatboy slim View Post
    i've fit them dry but some of the american forums use copper gasket spray. apparently they can be re-used. time will tell as i have re used mine for the first time although the car did not actually run and cometic say this should be no problem
    Something to think about for the future, thank you.

    Quote Originally Posted by Forest_rallying View Post
    I was advised by a well reputed competition engine builder to use a a thin coating of Welseal on a MLS gasket.
    That's great, thanks - do you mean a thin coating all over, or just around water and oil ways? Just wondering about how it interacts with fire rings?

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    Re: Cometic MLS head gasket fitting method

    although it seems wrong, i dont think all over would hurt ( as long as its very thin) almost all composite gaskets actually have a sprayed on coating of something sealant like

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    Re: Cometic MLS head gasket fitting method

    Ive always fitted them dry. As said above on freshly skimmed head and block.
    I have reused one on a pinto once. I had no time to re-order one and car was due out the following day rallying.
    I covered both sides with a thin coating of copper grease that came in a aerosol tin. I have to say that engine lasted well over a year, before it broke a spring and droped a valve.

    Personally i would always fit a new gasket but if time is against me again in future, the method i mentioned worked for me and i would do it again.

    Jonny

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    Re: Cometic MLS head gasket fitting method

    I never had problems dry on Honda's which are almost polish skimmed. The first one I fitted to a Pinto was fresh shimmed but more coarse and little leak of water. I was already using Hylomar on Jaguar single metal layer gaskets for the same reason. Used Hylomar and bingo, no more leak. I have reused lots of them, take them apart, clean them with Thinners and use Hylomar between every layer.

    Almost 100% sure Wellseal will do the same for a Pinto but I would not give it a try on a Jaguar. You need a thicker layer and stronger. The reason you best use an extra sealer is only because most older blocks are not fine (re) grind. The Viton layer is really thin and can not "close" the coarse lines. The Hylomar can and will. Jaguars are an other story, you can grind until the are spot on because there will be no head left to grind. You really need to close "gaps". The Hylomar did it for me all the time. BTW, I no longer use single metal on Jaguar's, also Cometic and never ever had a single issue since then.

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    Re: Cometic MLS head gasket fitting method

    Thanks for the responses everybody.

    I've heard a couple of racers (racers who are engineers and who build their own engines) struggling to get the Cometic MLS to seal on a Lotus Twincam due to the cylinder heads inherent flexibility. I'm not rebuilding a twincam so it's not relevant to my initial question but it might open up some more discussion about this subject and whether anyone else has any issues.

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    Re: Cometic MLS head gasket fitting method

    for me, i like the fact a mls cant have its fire ring blown out, but also dislike the fact the things have no give in them, which is why on pintos i either use ARP studs and a conventional gasket, or MLS and std bolts

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    Re: Cometic MLS head gasket fitting method

    interesting topic.
    and we are talking about cast iron block and cast iron heads.
    for my knowledge mls are better when used on a cast iron block and alloy head.
    what do you think?

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    Re: Cometic MLS head gasket fitting method

    I've used MLS in any combination and always sealed as it should (with Hylomar). Also fitted and MLS and ARP (most of the time because I always use ARP if I can (not standard blocks). Possible it can "give" less but i thing you would be surprised how much flex there still is. You can never get the relief complete out of it when you torque the head. So this is the flex still in and maybe we don't need flex??

    At least, I've never had any problems with these gaskets and currently to me the best gaskets for Mini's, Jaguars, MG, Triumph etc.. which sometimes have to be sealed with minimum metal between 2 cylinders.

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    Re: Cometic MLS head gasket fitting method

    Can not believe it would give an issues in a Lotus or any other combination. Unless you do it wrong or don't use sealer where needed (and did it wrong). Nor do I believe you need an iron block and alloy head. In USA the use them in any kind of V8 combination.

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    Re: Cometic MLS head gasket fitting method

    Quote Originally Posted by onyd View Post
    Can not believe it would give an issues in a Lotus or any other combination. Unless you do it wrong or don't use sealer where needed (and did it wrong). Nor do I believe you need an iron block and alloy head. In USA the use them in any kind of V8 combination.
    Lotus had problems with the cylinder head during early testing and couldn't get the gaskets to seal. I believe they had to change which casting foundry they used to get a better made head. It still leaked and then the cylinder head gasket was changed to a copper faced gasket to solve the issue so I think the issue is to do with the head in that case.

    It would be interesting to hear from people who have a Lotus T/C with a Cometic head gasket and relay their experiences.

    I'll be using the Cometic with an aluminium block and head.

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    Re: Cometic MLS head gasket fitting method

    Until date, none of the engine builders I know was able to seal a Jaguar with a Cometic gasket. I'm talking about Jaguars with fairly damaged water channels. Time after time I've saved them with my tube of Hylomar (and the knowledge).

    Unless the the Lotus casting is leaking water (not the surface against the engine) I would be surprised I would not be able to seal it.

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    Re: Cometic MLS head gasket fitting method

    A good friend has a BDA head with some corrosion damage around the water openings. They do not extend into the area around the combustion chamber. In looking at it yesterday, we decided that skimming the head would not be the best idea, because this head is going on a street engine. It had been skimmed before and additional skimming would raise the compression ratio out of the range of available pump fuel.

    I have repaired aluminum casting with Devcon F with good results. Anyone have an opinion on using this product to fill the corroded areas? The head would be returned to flatness using a lapping plate.
    Last edited by greengoredstop; 20-05-2017 at 02:58.

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    Re: Cometic MLS head gasket fitting method

    If I remember correctly Devcon F can be used up until 120 degrees Celcius or there-abouts.
    Would think that's not high enough.
    Some time ago I had a BDA head here from an engine on which 2 types of coolant were mixed with alot of corrosion as a result.
    A friend specialices in alloy welding and he repaired the head.
    See photos of before and after.



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    Re: Cometic MLS head gasket fitting method

    Quote Originally Posted by greengoredstop View Post
    A good friend has a BDA head with some corrosion damage around the water openings. They do not extend into the area around the combustion chamber. In looking at it yesterday, we decided that skimming the head would not be the best idea, because this head is going on a street engine. It had been skimmed before and additional skimming would raise the compression ratio out of the range of available pump fuel.

    I have repaired aluminum casting with Devcon F with good results. Anyone have an opinion on using this product to fill the corroded areas? The head would be returned to flatness using a lapping plate.

    There you go this is good gear may be of some use for you ,


    http://www.belzona.co.uk/en/applications/engines.aspx

    Belzona 1111 (Super Metal),

    Belzona 1511 (Super HT-Metal)

    Cheers

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    Re: Cometic MLS head gasket fitting method


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    Re: Cometic MLS head gasket fitting method

    Thanks guys, I will pass this along.

    Rob

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    Re: Cometic MLS head gasket fitting method

    Devcon Temp range
    120 F wet. 250 F Dry
    Please confirm if this would this be suitable?
    Attached Files Attached Files

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    Re: Cometic MLS head gasket fitting method

    Used Belzona 1111 for filling ports many times, excellent stuff!

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    Re: Cometic MLS head gasket fitting method

    Quote Originally Posted by James Jordan View Post
    Devcon Temp range
    120 F wet. 250 F Dry
    Please confirm if this would this be suitable?
    120 F wet is 51.6 C my thermostat opens at 82 C and temps can go above 100 C

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    Re: Cometic MLS head gasket fitting method

    You should never use sealant on a high pressure machined gasket face, your actually creating a leak path by doing that. Re. the cylinder head, Belzona is a better product, ive seen it used in the offshore industry on pitted steel pipework flange faces for very high temps and pressures up to around 120bar.
    Last edited by Erikmex; 27-05-2017 at 14:08.

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