Head gaskets are available in a variety of materials, and the type of head gasket material you choose for your engine should be influenced by the surface finishes of your engine block and cylinder heads.

In today’s video, SCE Gaskets‘ Ryan Hunter will walk you through different head gasket materials, ranging from the hardest—Multi-Layer Steel (MLS) head gaskets, to the softest—copper head gaskets.

There is an optimum surface finish for each type of head gasket material to achieve maximum sealing performance.

Roughness Average (RA) is a unit of measurement for measuring surface finishes. The RA number is the arithmetic average between the highest of peaks and lowest of valleys on any given surface.

Hunter uses a profilometer (a specialty shop or lab surface-testing tool used to measure RA) to help you evaluate what the RA level of your engine block and cylinder head surfaces might be.

A Quick Guide to Matching Gasket Types to Surface Finishes

Copper Head Gasket

Will withstand a wide range of surface finishes due to its softness and malleability. The copper will conform to the mill marks on the block or cylinder head because it’s a softer metal than either engine piece.

Composite Head Gasket

Works well on surface finishes as rough as 100 RA, but can suffer from poor sealing on extremely smooth finishes. The sweet spot would be between 30 and 100 RA, Hunter said.

15 RA (the approximate smoothness of something like your crank journal) would likely be too smooth for composite head gaskets.

Embossed Steel Head Gasket

Very strong. Requires a smooth surface to perform to its potential. The roughness ceiling would be about 60 RA, and anything lower should mate well with embossed steel, Hunter said.

MLS Head Gasket

The hardest of any gasket material. As a result, it requires the smoothest surfaces.

Hunter said that SCE’s MLS gaskets can seal up to 60 RA, but that a smoother surface finish is recommended.

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There is much more to be learned from Hunter’s demonstration. Check it out now: