I got an email seeking some help, that I am not sure I can provide, perhaps some of you may have some insight. I seem to remember having seen this issue before somewhere in discussions. Any idea...

Kindly advised recently our vessels main engine cylinder head (wartsila type
:6l20 ) have leakage of water from cyl. Head exh. valve seat.
This seat is new design with one o ring (old design was with 2 o rings).
We checked every things and so many time we changed seat and oring but leakage was not rectified Recently we received new cyl.head (6 pec) and after installation on engine after few day again leakage happen.
For your kindly information our engine work with diesel oil.
I work with this type engine so many years but they were as generator (alternator with constant speed with burn heavy oil) and we have not any problem.

I will appreciate if you can help to us and any advised to me

Cant help to think perhaps you have counterfeit parts? Not sure if there are any service letters from Wartsila on this.

Where the cylinder head was replaced and the issue persists it sounds like there may be an issue of water flow to the cylinder head or there may be contact between the piston and the valve. Where the valve seats get very hot any kind restriction in the water flow will cause issues with seats
I would pull the cylinder liner and check there is no water flow restriction around the liner caused by dirt or corrosion.
I would also check the liner for cracks that would allow combustion gasses into the cooling system affecting the water flow and check seating surface between the block and the liner for fretting damage.
I would also check the piston, wrist pin & bushing and the bottom end for excessive wear.
I would also check to insure the compression clearance between the top of the piston and the cylinder head is correct.

The Diesel Electric PSV I am sailing on has 4 Alternator sets, all Wartsila W9L20. When the ship first came out all the cylinder heads had to be changed because of leaking exhaust valve seats. (I think inside the first year) When the changed heads also started leaking the people on board started to get really worried, but then worked out the ones that were leaking were the original ship's spares that had been put on board when the ship was built.
Wartsila claimed it was caused by the workers in their factory not following the correct procedure to fit the seat into the head. The workers have been re trained and no problems since.
Maybe you should check with Wartsila that the seats are being changed EXACTLY according to their instructions, or have the heads re- conditioned by Wartsila.

Another thing that I noticed on these engines is that the crankcase explosion doors do not have a retaining groove to hold the "O" ring seal between the opening valve and the rest of the door. I imagine that in the event of an explosion opening the door, the "O" ring would drop down and prevent the valve closing properly, thus permitting air to flow into the crankcase and cause the secondary explosion that the explosion door is designed to prevent. I think the engine has been " value Engineered" and then built in China.

Good Luck BP