Paul57

Has anyone had bad luck with Cometic head gaskets...or good luck?? I was thinking about using their .040.

poltergeist 02

iTrader: (65)

Seems to be hit or miss depending on who you talk to. IMO the GM MLS gaskets are a better product and are a little more forgiving when it comes to a proper seal.

Paul57

Does GM make a .040-.041 MLS gasket??

therabidweasel

iTrader: (5)

GM doesnt. Hit the cometic with copper seal and put it in. Lots of guys on here run cometics.

PREDATOR-Z

For Cometics the surfaces of block and heads need to be totally true.
I've used them quite a few times with copper sealant spray and never had an issue.

Paul57

If you use the copper spray do you just apply it to the top and bottom surface or between each layer too??
I found this interesting info... http://forums.bimmerforums.com/forum...asket-Question

PREDATOR-Z

Top & bottom

RezinTexas

I'm running them with light copper seal spray. No issues, would use again if you're looking for a custom thickness.

Pipelayaz

iTrader: (2)

Where do you get the copper spray from? Any certain brand?

Burken01

iTrader: (88)

Auto zone , permatex

LilJayV10

iTrader: (39)

How many people are running the cometic .040 on a stock bottom end? I know the pistons are "proud" or stick out of the block some.

PREDATOR-Z

On average stock LS1 pistons stick out of hole about .006/.007
With .040 gasket that will leave .034/.033 quench.

ckpitt55

iTrader: (4)

read through that, cliffs for anyone interested:

-Copper spray is a crutch for poorly machined deck/head mating surfaces. If they're on the money there's no need for copper spray. There was also talk of the coating affecting the sealing effectiveness of the viton rubber in the gasket.

-There was also talk of gluing the layers of the mls gasket together using a high-temp loctite 3020 adhesive to prevent leaks between the layers.

-Separate gasket layers
-Spray each layer with adhesive and assemble to block
-Torque to 30% of final torque and wait a half hour
-Torque to 90% of final torque and bring engine to operating temp.
-After engine is cool, loosen hardware then retorque to final values.

All of the above info is from an F/I forum with guys running lots of boost, not sure how much of it translates to NA motors. I personally have no experience with either technique, figured I'd just add what I read to the discussion here.

therabidweasel

iTrader: (5)

Ill add that I had 3 sets all due to non headgasket problems. One I noticed that the surface had some particles on it straight out of the package. I used a cleanroom wipe with isopropanol and a very light touch and discovered the particles were viton wiping right off, as would wet paint. Got it looking as good as I could, several thin coats of copper spray with a little drying between and it held for 2k miles until I had to get in the motor for other reasons. It may be a crutch, but if you use it right I dont see how it could hurt.

As far as my simple mind can think only clamping force could really stand up to chamber pressure, hence extra head bolts etc. . .I cant see any glue, paste or rubber seal keeping you from lifting the heads. But im just thinking out loud I do not know for sure

DietCoke

iTrader: (18)

my cometic .040s are on their fourth re-use. i might replace them next time... lol. copper spray ftw

Quick Ranger

iTrader: (2)

Was your block decked at all prior to first use? I'd like to run these .040 gaskets, but my block hasn't been decked, only the heads have. I don't have alot of exp with Cometic gaskets.

PREDATOR-Z

Please be careful about decking the block. Tight quench is good but by decking the pistons will stick out more.
Quench = Compressed gasket thickness - piston out of hole value
Good quench for street should not be much lower than .030 and that is a bit tight. Remember metals expand when hot.
IMO do not deck block unless necessary.
.035 to .045 quench range in street is more than adequate.

DietCoke

iTrader: (18)

I have stock deck height, it was only cleaned up for the reuses with a 3m surface prep pad on a dewalt drill... hardly sophisticated methods. My pistons are .004 out of the hole and I use studs.

LilJayV10

iTrader: (39)

I'm glad you posted that. I was wondering how tight you could run the quench before you ran the risk of the piston smacking the head.

How did you measure to see how far the piston stuck out?

ckpitt55

iTrader: (4)

Get an indicator bridge and zero a drop style indicator on the deck surface. Then carefully position the indicator over the piston, and turn the crank until the indicator shows that you are at TDC. This occurs right at the point where the indicator needle stops rising and begins to fall. This indicator reading at TDC will be your piston stick out.





You can also figure out your deck height from this measurement. You know the length of your stroke, the length of your rods, and the compression height of your piston. If your piston is sticking out 0.006", then you know your deck must be 0.006" shorter than your height at TDC (1/2 stroke + rod length + compression height of piston).