Ok here goes. Rebuilt both 502 Gen IV new cams and used Gill exhaust with long risers. Ran it for 2 hrs and while flushing noticed a clacking sound and had water in the oil of one engine. The machine shop listened to it and thought it was a bad lifter (new with cam).

I pulled the risers and exhaust and saw #7 looked wet. I have since pressure tested the cooling system (Block heads intake to 50 psi air) no leak down. Pressure tested exhaust manifolds with both air and water with no signs of leakage as well as oil cooler.

Have not pressure tested stainless risers due to not knowing how to plug the 3 holes at the discharge side. Any suggestions on how will help.

My question is would a bad lifter or any other valve train issue cause reversion? If my risers check out OK I'm stumped.
Thanks for any input!

What cam are you running ? I was told that Gill's can not have more than 230 in duration

If only #7 was wet and #8 was dry ,,,then i think its not reversion !
Usualy its on both sides of the block .

#8 Might have been wet however I am running the same cam in the other engine with no water in the oil. Is it possible the cam is degreed wrong? Or???

That may be an option,,,or,,,,,,haedgasket ?????

Not sure if this is correct, the factory 420 cam (228°/236°) was Merc built with Gils.

You need to make sure you are using the right head gaskets you can mix match heads to any generation block but you need the right head gasket or you will fill the engine with water. The coolant holes in the heads are diffrent from generation motors

What cam are you running?

An exhaust valve not sealing well can cause reversion. A bad lifter would only cause reversion if you tightened the rocker down too far and held the exhaust valve open. Not sure exactly where the limit is with Gil exhaut but it's somewhere in the area of 230-240 degrees @ .050.

Thanks for your input everyone. Both engines were rebuilt the "same".
Same head gaskets same cams, I'll get specs on here soon to answer questions. One runs good no water in its oil.