Head Gaskets: Steel Shim vs Composition Head Gaskets?

[Mildcat]

Steel Shim Head Gaskets or Composition Head Gaskets in 401/425?

[Dr. Frankenbuick]

You would want the steel shim gaskets if you are just removing and replacing stock heads on a stock engine. That way you keep as much quench as possible and do not lower the compression. You would want the composite (thicker) gasket if you were rebuilding the engine and decking the block to square and reducing deck surface to use a thicker gasket. The steel shim gaskets are no longer made and are getting hard to find. The aftermarket gaskets are plentiful, but are .015"-.020" thicker. That is simple to take from the deck if rebuilding, but costs .5 in compression ratio and less quench if replacing a steel shim with a composite in a stock engine.

[telriv]

On ALL the engines I've done NONE have measured more than 9.75-1. Many are even less from the factory. On a 401 the head gasket is approx. .015"-.016" compressed with a bore diameter of 4.250 less approx. .008 when compressed. A composite gasket can be anywhere from .033"-.040" compressed, depending on the manufacturer, & since they will fit ANYTHING from a 364 up to an over bored 425 the bore diameter starts at approx. 4.420 less approx. .010 compressed. On a 401 this means a loss of compression ratio from about .5-.7. Assuming you had 9.75-1 to begin with you are now at 9.25-9.05 with an increase in the squish/quench from the ideal of .025"-.050". On a 425 it means a loss of .4-.6 loss, also with an increase in squish/quench area. From the factory with the average in the hole of a minimum of .040 (RARE) to the more average of .055" your quench/squish area is .055"-.070". Still not ideal but better than .100" give or take. Many wonder why the rebuilt "Nail" just doesn't seem to run as well as the worn out stocker that was just done. Another reason why I got involved with making CUSTOM FORGED pistons for the "Nail" as there was just NOTHING out there in a cast, off the shelf piston that can cover ALL the variables that can pop up when rebuilding. I have some steel gaskets available, not many.
Just my thoughts on the subject.


Tom T.

[FatSo]

Can the steel gaskets be reused? how should they be cleaned if they can be reused?

[Dr. Frankenbuick]

Can the steel gaskets be reused? how should they be cleaned if they can be reused?

I would use scotch brite and then wipe with rubbing alcohol or prepsol if you have some. Then a light coating of copper coat and they are ready for duty again.

You can also use silver enamel paint and assemble slightly wet, but it will be difficult, if not impossible, to get apart again using that method.


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