Grog

I've been chasing a really bad "water in the oil" problem since March of last year when I had the heads cleaned up, and replaced the head gaskets on my 502 in preparation for a 5-6 psi blower.

After several top-end teardowns and pressure checks, we found that an area on the deck of the block between the water passages and the oil galley had a flatness problem (approx. .020" over a 5" span). I had to tear out the motor apart and machine the deck flat. It is back together now and seems fine.

My motor builder tells me that on my era of 502 block ('99- ?), Mercruiser outsourced the machining process to an outside vendor and this defect began to occur. The deck surfaces on the defective blocks look polished instead of seeing fine tooling marks in the surface where it had been machined.

Has anyone else ever heard of this situation before?

Sadist

That standard 502 was not touched by Merc, there would have been no outsourcing of machine work since it was good to go from the "general". I'd guess something caused the deck to warp prior to configuring for the blower, or during (head overtorque, killer overheat...)
The decking of the block would certainly have fixed the problem..

PatriYacht

If the deck has a shiny look to it, that would suggest to me that GM was getting the cutter too hot while machining. That would definately cause an uneven surface as the iron expands and contacts under the cutter. All it would take is a bad batch of carbide inserts getting dull early. Thanks for the heads up.