Sizing head gaskets
Thread Starter
Melting Slicks
Joined: Feb 2000
Posts: 3,299
Likes: 0
From: Beltsville Maryland
Sizing head gaskets
I'm considering using the Cometic head gasket instead my the current Felpros.
Cometic recommended me using a 4.135 bore gasket on my 4.125 bore motor. They said the gaskets will be .010 - .015 bigger allowing for the cut. The Felpro gasket is 4.190 bore. That is probably alot larger than need to be, but Felpro does not offer a ton a different combos (bore/thickness) as Cometic.
Feed back please.
Cometic recommended me using a 4.135 bore gasket on my 4.125 bore motor. They said the gaskets will be .010 - .015 bigger allowing for the cut. The Felpro gasket is 4.190 bore. That is probably alot larger than need to be, but Felpro does not offer a ton a different combos (bore/thickness) as Cometic.
Feed back please.
Melting Slicks
Joined: Dec 2001
Posts: 2,025
Likes: 1
From: Billings MT
Hey, I went through this with Cometic just last year.
I ended up having to order 2 sets as the ones the salesman told me would work (also .010 larger than bore) ended up being to small!
They will make you buy another set if it doesn't work, no returns.
The problem was with the chamfer at the top of the bore, it was just enough to where the gasket would hang into it slightly, which would cause a source of preignition.
The other problem is that the gasket hung into the combustion chamber, also another source of preigntion. The bore on these gasket is cut ROUND unlike the D shape of the felpro gaskets that give you clearance.
I ended up using a 4.200" gasket bore on a 4.155" cylinder bore.
I have also re-used these gaskets and they have worked great.
I ended up having to order 2 sets as the ones the salesman told me would work (also .010 larger than bore) ended up being to small!
They will make you buy another set if it doesn't work, no returns.
The problem was with the chamfer at the top of the bore, it was just enough to where the gasket would hang into it slightly, which would cause a source of preignition.
The other problem is that the gasket hung into the combustion chamber, also another source of preigntion. The bore on these gasket is cut ROUND unlike the D shape of the felpro gaskets that give you clearance.
I ended up using a 4.200" gasket bore on a 4.155" cylinder bore.
I have also re-used these gaskets and they have worked great.
Thread Starter
Melting Slicks
Joined: Feb 2000
Posts: 3,299
Likes: 0
From: Beltsville Maryland
I have decided to use the Felpro 1003 instaed of the 1004's. The 1003 are the same , but with a bore of 4.166 compared to the 1004's 4.190" bore. My motor bore is 4.125 bore. I just be safe there. Yeah, I believe Cometics suggestion of using a 4.135 bore would be too tight, even thought they said to allow for another .010" for variances in the bore cutter.
Thanks for everyones input.
Thanks for everyones input.
Le Mans Master
Joined: Feb 1999
Posts: 6,172
Likes: 11
From: somers, ny
Yeah Cometic gaskets are great, but don't try to return them. They cut my water passages too small, then blamed Brodix. They wouldn't take them back and wouldn't expedite another set to me. Kinda low budget service for a high cost product IMO.
Thread Starter
Melting Slicks
Joined: Feb 2000
Posts: 3,299
Likes: 0
From: Beltsville Maryland
The one advantage of using the Cometic head gasket is that they can be reused.......to a point. The rep. at Cometic said that if the gaskets are run for a season of racing they should not be reused. Others , including engines builders using dynos can reuse them when the motor is apart for shorter periods of time.
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Melting Slicks
Joined: Dec 2001
Posts: 2,025
Likes: 1
From: Billings MT
wheelsup: I talked with a tech at Cometic a couple of times about reusing them. I have successfully reused the drivers side one after about 200 miles and I just recently reused the passenger side one after 2 race seasons (not heavy, but over 100 passes) and 8000 miles.
He said as long as the metal layers have not lost their tension, ie the embossed rings are still embossed and raised. They "should" be ok.
He also stated something that got me by surprise. Some parts of the Viton coating were coming off and he said the Viton coating didn't really matter. His instruction was to clean all layers and gasket surfaces very well using acetone and to coat the outer surfaces with hylamar of copper coat.
I cleaned everything really well and put a light coat of copper coat on and everything is working just fine.
He said as long as the metal layers have not lost their tension, ie the embossed rings are still embossed and raised. They "should" be ok.
He also stated something that got me by surprise. Some parts of the Viton coating were coming off and he said the Viton coating didn't really matter. His instruction was to clean all layers and gasket surfaces very well using acetone and to coat the outer surfaces with hylamar of copper coat.
I cleaned everything really well and put a light coat of copper coat on and everything is working just fine.