Re: cometic head gaskets
 

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.

Re: cometic head gaskets
 

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.

Re: cometic head gaskets
 

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

Re: cometic head gaskets
 

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.

Re: cometic head gaskets
 

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.

Re: cometic head gaskets
 

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 :)

Re: cometic head gaskets
 

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.

Re: cometic head gaskets
 

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

Re: cometic head gaskets
 

Listen to Rich.

Re: cometic head gaskets
 

Something else to consider on a SBC is the size of the dowel pins. The OE dowel pins are .309" diameter. If .3125" (5/16") pins are used the head can bind on the pins. This will prevent the head from clamping properly to the block in the lower corners. Several companies sell SB dowel pins that are actually 5/16" roll pins.