cometic head gaskets

[Jeff Stout]

Originally Posted by Jim Bailey

I have a simple practice that I use with MLS gaskets. The problem is with the stretch of the fastener. I use plenty of copper coat ( like a whole can on two gaskets). After the head is torked on, I let it set 24 hours. Then, "one at a time", I untork the fastener and re tork it to spec with one pull on the tork wrench. I've actually had motors stop weeping, doing this on the dyno. Right or wrong....works for me.

On my sbc I didn't spray coating as I was informed by many not to. If you had good luck spraying then I will on next rebuild for piece of mind as I run alot of nitrous and feel leary of not coating them. Thanks for the info.

[BillK]

Originally Posted by Jeff Stout

On my sbc I didn't spray coating as I was informed by many not to. If you had good luck spraying then I will on next rebuild for piece of mind as I run alot of nitrous and feel leary of not coating them. Thanks for the info.

You have to be careful with this as most MLS gaskets have a coating on them from the manufacturer that is there to help them seal. Putting another coating on them might actually make it worse. I prefer to go with whatever the gasket manufacturer recommends.

[RonP]

OEM head gaskets require a "smoother" surface finish to seal coolant and oil passages. The "rubbery paint" is there to provide a micro-seal against leaks. OEM head gaskets are beaded to provide an effective sealing load around these passages and the chamber.

A torque wrench measures torque, not friction as someone stated earlier.

Torque = friction coefficient x tension x thread diameter (for elastic region bolts).
Friction coefficient is generally 0.1 ~ 0.3.

Adding oil or other lubricant will increase the bolt tension over a dry or unlubricated condition. Something a friend and I did at work years ago with a strain gauged bolt to see for ourselves.

[SSDiv6]

In lieu of the Copper head gasket spray I would recommend Hylomar spray.
Do not use the Permatex/Loctite Hylomar sold at most auto stores; it's a watered down version of Hylomar.
The best Hylomar is the Yellow can industrial version.

[BillK]

Originally Posted by RonP

A torque wrench measures torque, not friction as someone stated earlier.

Ron,
That is correct and what I was trying to get at was the fact that the friction will significantly affect the preload on the fastener for a given torque. My choice of words were not the best

[Rich Biebel]

I have used Cometics with zero issues for at least 5 years. I have reused the same gaskets 3 times with no additional coatings and also another set 2 times with copper coat spray. This is a 15-1 compression engine and with or without the copper coat there was no leaks. Pretty smooth finished block and heads. I generally block sand the heads if they are off with wet 400 paper in a wash tank. Cometics work very well for me.

[RICK W]

Thanks for all your comments guys, the block is just machined too rough for those gaskets

[Ed Wright]

Listen to Rich.

[carl hinkson]

Originally Posted by Jeff Stout

On my sbc I didn't spray coating as I was informed by many not to. If you had good luck spraying then I will on next rebuild for piece of mind as I run alot of nitrous and feel leary of not coating them. Thanks for the info.

Jeff
I have always sprayed my Cometic head gaskets with Copper head gasket spray with no problems to date.

I have seen quite a few old Cup engines that have used cometic gaskets that were sprayed with Copper head gasket spray. If they are using it that's good enough for me.

[terry1]

Rick, are you going to be ready for the Miramichi NHRA races???
Terry K