OK, I am going to be puttting a set of Cometic .045s on my car with the new heads and cam shortly, and found some old threads where they were leaking, but see that alot of people are now running them successfully. My question is this, what prep is required to guarantee a leak free experience? My heads are milled with them in mind (high RA number or something like that), and I keep seeing where surface prep is crucial. My block has had 2 previous H/C setups, and I'm worried/wondering if my block surface is good? Both times GM MLS gaskets were used....

Thanks, Shawn

 

Block is ok. I always spray copper coating on mine when installing them. I have put on probably 40 sets of Cometics and I have yet to have one come back leaking. I have them on my own car and I spray 300 worth of bottle.

 

Just make sure everything is clean, and re-torque in sepquence until everything is tight. I had to re-torque a few times to get all the bolts the same. I prolly went over them 10 times over a period of a day or 2. On the engine stand of course.

 

Hate Cometics.
Won't allow them near my car or any friends cars.

 

I put them on my car with freshly surfaced heads and block. I used copper spray on mine and retorqued after a day and have had no problems. I have run 6 bottle of N2O on it also. My friend had a lot of problems with his cometics but he had 98 heads that have a low spot.

 

I just made sure both surfaces were very clean. I used grey scotchbrite and MEK to remove any last bit of debri or film. Tqed the heads several times till Tqs leveled off. I ran these heads gaskets last year for 14 months with no leaks between 600-710 rwhp spraying up to a 300 shot. Probably sprayed 400+ lbs of nitrous through the motor. Same head gaskets the entire time.

 

I share the same concern about the cometics. I just bought AFR's milled to 61cc and I bought .045 cometics (3.910 bore). I called cometics and they pretty much said not to worry as long as the surface was flat. We will see what happens when the AFR's get here in 6 weeks or so.