I have a 502 that has developed milky oil. At which I assumed to have cracked/rotted heads. But upon disassemble I found water in the #8 exhaust manifold port and some water in that cylinder. I inspected that combustion chamber and found a bad seat on the intake valve. (I could see daylight around the closed intake valve) There are no visible cracks in that chamber. The engine has gil manifolds and risers that are brand new. All of the other exhaust ports on that head show signs of water as well.

My question is can one dead cylinder cause excessive reversion? causing the oil to milk up? and would it bring water closer to the other 3 exhaust ports on that head? Any help would be greatly appreciated.

Engine has merlin heads with a similar cam to an hp 500. it is a hydraulic roller.

A dead cylinder can and will pull water back.

As a heads up, the HP500 with Gills had a tendency to revert, so the later ones they switched to a much taller riser to keep this at bay.

Pic is of the tall style:

Sounds like its time for a valve job and have them check the seat pressure. I just went through two dropped valve seats, one on each engine. One cylinder can definitely cause milky oil.

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With a dead cylinder where exactly does the water enter the oil? Filling up the cylinder and compressing through the rings?

When the valve job fails it sucks water back in the intake, and also gets into the combustion chamber. starts showing signs in the valve cover first.