Installing Cometic Headgasket

[johnnyt]

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

[sinistaGTR]

dont use them there shit, we faced my head and block used one and it leaked like a siv. went out and bought a trust one worked a dream, pay the extra money and get good stuff.

[johnnyt]

dont use them there shit, we faced my head and block used one and it leaked like a siv. went out and bought a trust one worked a dream, pay the extra money and get good stuff.

ive already got the cosmetic so i dont really wanna but another:(

johnny

[sinistaGTR]

well best bet is either to try it or sell it and get a good one, theres many storys of them working fine just after my experience i would never touch one again.

[johnnyt]

any one else got any advise?

[Cubes]

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.

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

[sinistaGTR]

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]

wow $440.. :S

They are near half that price from japland or sau sponsors.

Damn I'm a tight arse. lmao

[Cubes]

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.

[DivHunter]

Probably a good thing I went for a Tomei instead of the Cometic then.

[Sambo33gtst]

i used a cometic head gasket in my forged rebuild. Slightly bored and honed bottom end with arias pistons etc etc....beuat compression and no leaks. But i went slightly oversized

[Pauly33GTS-t]

Sinista, you got yours before car toys was sold i think, maybe you walked in on a clearance sale. I know this lass, her uncle and auntie just sold car toys or something apparently.

[Cubes]

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.

[proengines]

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]

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

[johnnyt]

well decided that i am going to strip the engine for the second time to get the block decked:(

then reassemble and use the cometic gasket,i cant understand why my engine builder and machinest didnt deck the block:(.bloody pissed off!

johnny

[sinistaGTR]

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]

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]

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.

[Cubes]

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

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