Cometic head gasket??
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Joined: Sep 2009
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From: Frozen Tundra, WI
Cometic head gasket?? Has anyone had bad luck with Cometic head gaskets...or good luck?? I was thinking about using their .040.
Last edited by Paul57; Apr 28, 2013 at 05:30 PM.
Thread Starter
TECH Resident
Joined: Sep 2009
Posts: 859
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From: Frozen Tundra, WI
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
I found this interesting info... http://forums.bimmerforums.com/forum...asket-Question
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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
I found this interesting info... http://forums.bimmerforums.com/forum...asket-Question
-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.
Last edited by ckpitt55; May 1, 2013 at 07:40 AM.
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
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
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.
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From: BFE
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.
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.
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.
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.
How did you measure to see how far the piston stuck out?
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).
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).