Cometic Head Gaskets - What did you do to prepar the block?

[vettenuts]

Have been reading up on the requirements for Cometic head gaskets. They are needless to say quite stringent as far as surface finish and deck variation. A lot of guys seem to run into leaking issues. If you are running Cometics, how did you prepare the block (not worried about the heads, only the block).

[CollinsAuto]

Run the GM MLS never a problem. they still require a fine finish and very very minimal out of flat. you can also use the felpro MLS another good gasket. I have only seen leak after leak with cometics.

[ToddO]

I used a 3M Scotch-brite Roloc Bristle Disc on an angle die grinder. I have Cometic .040 gaskets with no problems. I have heard of people using Yamabond sealant on the gskets as well. I have never tried it.

[vettenuts]

Cometics doesn't recommend any sealant but rather dry installation. I have plenty of time to sort through whether to try them though, install won't be until spring (got to have something to plan over the winter). :)

[02reaper]

I cleaned surfaces with brake parts cleaner first, then sprayed the cometic gaskets with copper coat. Never had any problems out of them. They were a bitch getting off though. I guess the copper coat worked. One more thing is that whether your torquing them down with the stock fasteners or anything else, (I will reference the stock bolts torque sequence here) torque them down to the 22 ft lbs first and wait about 15-30 minutes and torque them again to 22 ft lbs. I would wait another 15-20 minutes and then do them again, just to make sure that they have got compressed good on the head before doing the two additional 90 degree turns on the long bolts and 90/50 on the short bolts, or whatever the gm book calls for on your engine for the rest of the clamping procedures. On something like the arp fasteners I would torque them in three steps such as 30/60/85 or so checking them three times at 15-30 minute intervals for each step. Hope this helps.

[CollinsAuto]

I prefer the razor and Honing stone method. I scrape and clean carefully to avoid knicking of the deck surface.I then take a very very fine 1000grit honing stone and gently rub the deck of the block. I do this to make sure that the deck it flat and clean. If i spot trash IE gasket etc I rescrape with the razor and recheck with the stone. Roloc disc is nothing but trouble.I still refuse to recomend use or install cometic gaskets. I have seen them waffle under pressures that a stock GM gasket doesn't even care about. Just my $0.02

I used a 3M Scotch-brite Roloc Bristle Disc on an angle die grinder. I have Cometic .040 gaskets with no problems. I have heard of people using Yamabond sealant on the gskets as well. I have never tried it.

[vettenuts]

You are the second person who has recommended a "honing stone". Where would I find one to purchase? Snap-on has a nice (and for Snap-on reasonably priced) machinists straight edge, haven't looked there for the stone though.

[CollinsAuto]

any place that sells hunting knives or serious kitchen utensils should be able to direct you to a very fine grit honing stone. I prefer the larger ones at least 8 inchs long with a very fine 1000 grit finish. Alot of hunting places carry stone like these.

DO NOT USE A ROLOC DISC EVER TO CLEAN A DECK OR INTAKE GASKET SURFACE.

I do not care if you are gods gift to the 90degree grinder you're going to create surface irregularitys with that damn thing.Not to mention all the abrasive going into the engine. When i was a shop forman before I had my own place I used to lock vice grips onto peoples ass's if I saw them using one to clean intake mating surfaces or cylinder head mating surfaces.

Make sure to prep and clean throughly the deck. when using the honing stone I prefer to use some sort of penatrating or light oil to lubricate the stone. PB blaster Wd40 Tap magic all work fine. Remeber though with the stone you not trying to resurface the deck just gently rub it clean.

after your finished with that use some mineral spritis to remove any abrsive grit and dirt then wipe clean with a Brake cleaner soaked rag.

This should pretty much guarentee a good seal.


You are the second person who has recommended a "honing stone". Where would I find one to purchase? Snap-on has a nice (and for Snap-on reasonably priced) machinists straight edge, haven't looked there for the stone though.

[vettenuts]

Thanks for the information, any concerns with particulate in the cylinder bore?