If the black coating on the OEM head gasket isn't enough to seal the head to the barrel, then there's something wrong, period! That viton coating is exceptionally thin (approx 0.025mm) and does promote sealing, but also ensures the minimum of expansion (and also movement) between the mating surfaces.

Its thickness also means it's easily damaged, and therefore shows where leaks have occurred, or are beginning to become a potential problem. This should be warning enough to prevent erosion around the stud holes if the top-end is properly maintained. Clearly Al's wasn't!

Silicone sealant takes 30~60 minutes to "set up", and once (an old 80's 4-stroke motor!) assembled, shouldn't be run for 24 hours to allow it to cure completely. Something many people don't know.

You also have no control over the thickness of sealant, and it's unlikely you will ever reproduce two identical builds. Not exactly good for a high performance engine! It was designed for mass production car engines and cost-cutting.

Using a very light smear of grease on a base gasket is acceptable on a road bike, but unnecessary on a race bike, as it should be apart long before the gasket has time to bond to the cases.
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Andy.
NSR-WORLD.COM

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