I'm getting ready to assemble a 2003 496HO and i was wandering about ring gap. My manual says .012-.018 gap on top and .017-.025 on the 2nd. I have heard that the factory ring gap is to tight and can destroy the piston. Does anyone know what a "safe" gap would be?

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cp,
What parts are you using ? Stock Mercruiser ? Aftermarket ? How many hours did the engine have on it and did you have to bore it or is this a re-ring "freshen up" type of deal ? Are you increasing horsepower in anyway ? Blower ? New cam ? Etc etc.

If the engine has been running since 2003 with the factory ring gaps, that should tell you something.

Whatever you do, a little bit too much ring gap will rarely hurt anything and is certainly preferred over not enough.

Bill Koustenis
Advanced Automotive Machine
Waldorf Md

Its an 03 merc engine but has very few hours. It didn't need to be bored. I'm planning on going on the upper end for clearance but i wanted to get some input from others.

Who's rings are you using ? It really should not matter much, but I generally use the recommendations of the ring manufacturer. They do vary a good bit from one manufacturer to another.

If they are the metric 1.5mm rings, use .020" - .022" top ring, .022" - .024' second ring. Factory GM gapped many to tight .015" -.018" and in marine high rpm -hot usage they butted and broke pieces of the top of the hypereutectic cast piston. This is one of the things that really helped to destroy some of the reputation of the stock pistons!

Best Regards,
Ray @ Raylar

Thanks Ray!