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Installing Cometic Headgasket

johnnyt

By johnnyt,
in Engines & Forced Induction

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johnnyt Rising Star

johnnyt

Posted
Posted

hey guys i just got my rb26 bottom end (rods crank pistons assembled)

problem i have is that i was going to use the cometic mls gasket in my engine but the face of the block hasnt been machined, and ive read on here some guys cometics have leaked.

so can i use the cometic even though the block hasnt been decked?

and is there anything i should do to make to make it seal better?

johnny

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https://www.sau.com.au/forums/topic/164488-installing-cometic-headgasket/
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Cubes Grand Master

Cubes

Posted
Posted

Bl4ck32 and I both run a cometic MLS, had the motor built up by the same bloke at the same time.

The head wasn't faced but the block was decked.

No leaks, all good. I've ran up 50,000km's over 2 years Bl4ck32 has had his going for the same amount of time.

Some do have issues with the Cometic MLS.. No idea why. Yet others who use them all the time have no issues. Maybe its a certian finish required? :S

Sinista.. I'm about to rip the head off mine to sort out too much oil holding in the head. Where did you grab your trust item from?

I'll be going one of those 'just' incase. :3some:

EDIT: I require a 1.2mm 87mm rb26dett headgasket. Nengun state they are now discontinued. :spank:

sinistaGTR Grand Master

sinistaGTR

Posted
Posted

Hey cubes got mine from believe it or not lol cartoys they were the cheapest i think autobarn may have one they were also doin good prices i was very very suprised. Mine cost me 440, it was just a real kick in the teeth after spending money on a cometic one lol.

Cubes Grand Master

Cubes

Posted
Posted

I've since done a little more research.....

The commetic needs a surface Ra of 60 or better. Which is apparently not that easy to do.

It needs a very slow milling table feed and a very fast head speed on the cutter to get it.

If not.. it will leak like a siv. :S

Some also use a copper spray IF their cutter is unable to provide such a finish.

Cubes Grand Master

Cubes

Posted
Posted

I'm going to give it a shot reusing mine. :S

Apparently hit it with gasket remover, wipe off the old crap, then scotch brite it and finally hit it with copper cote and wack it on. I've spoken to a few blokes that have reused theirs a few times over with RB's. One is on ct.com, used his 4 times on his rb30. :huh:

proengines Rising Star

proengines

Posted
Posted

There's nothing at all wrong with Cometic gaskets. What you occasionally find though that is someone stuffs up fitting it and rather than admit it, they blame the parts. You do need a good surface finish for any MLS gasket and the surface also needs to be flat. Run a flat single cut file over the block and it will show up and high spots, remove them and you should be fine. Any decent machine shop can give the finish you require for the gaskets, CBN and PCD milling cutters do it easily.

ACL thinks the gaskets are good enough to put their name on and you can imagine the testing they have done trying different gaskets.

Craved Grand Master

Craved

Posted
Posted

http://www.cometic.com/faq.aspx

"What surface finish is required to us an MLS head gasket?

A surface finish of 50 RA (roughness average) or finer, is recommended for a proper gasket seal. Anything rougher may conflict with the gasket design. "

Also

"Why does Cometic recommend MLS gaskets to be installed dry?

Cometic Multi-Layer Steel (MLS) head gaskets go on dry because they are coated with a sealant. Each MLS head gasket is coated with a .001" thick viton rubber that is bonded to the outer stainless steel layers. Adding an additional sealer can hinder the performance of an MLS head gasket. "

even with this second quote, i used a gasket sealant _ hylomar i think. spray on light coat only

sinistaGTR Grand Master

sinistaGTR

Posted
Posted

ok....

paully: no autobarn had them for 460, it wasnt a clearence sale or any shit like that.

Everyone else: We used copper spray plenty of it everything was done properly we even rechecked the block and the head once we pulled it off. we put the trust one in and straight away no leaks, i think there just a poorly made cheap item, yes the work sometimes but not others goodluck if it works. Just giving my experience on what happend.

Darius Explorer

Darius

Posted
Posted

I too have had issues with the Cometic gaskets not sealing. Viton doesn't seal for $hit as a general material property and head gasket applications are no different. It has a higher temperature resistance than EPDM but not nearly as easy to seal.

Even though both my head and block were decked and had mirror finishes to them, I still had a coolant leak on the left rear of the head. The leak was only a seep but it still dribbled a couple drops every time I parked and I didn't want to risk blowing it so I had to pull the head again. Total PITA if you have HKS cams without the head stud recesses to leave the cams in.

I'd spend the extra money for anything BUT a Cometic. There is a reason that they are so cheap, it's because they suck. Good for you if you can get it to seal, but most will have troubles without finishing both the head and block.

BOOSTD Mentor

BOOSTD

Posted
Posted

I use VHT copper head gasket sealant on all my metal gaskets, works a treat. Rocket and some good auto shops sell it.

Cubes: I have a second hand 1.2mm 87mm Trust head gasket. I have re-used these before, just separate the layers, strip the old sealant and recoat with copper spray. works a treat. I wasn't convinced it was ok until Peter from Advan Advised he does this on a daily basis with no problems. It is a bit of dicking around but heaps cheaper.

  • 3 months later...
Cubes Grand Master

Cubes

Posted
Posted

Well I stripped downt he cometic cleaned and sprayed with hylomar.

Its leaking between an oil and water galley. So I'll be going trust this time around 'just' incase. lol :down:

Nengun is cheap $196 delivered BUT I can't be bothered dicking around waiting months for them to deliver.

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