Hie experts out there, I have a tug equipped with 2 sets of Niigata 8 MG 25 BX, it's a 40-year old tug, don't ask me why it is still in service, owner's sentimental tug....anyway, let keep to my point.
I have a hydro knock on one of the unit, con rod bent, liner bottom part broken etc, for those of you who are not familiar with this engine, it's 4 stroke medium speed.
now, boss wants to know the root cause of it, EVERYONE in the department knows is water knock, but question is WHERE DOES THE WATER COME FROM....alright i know you have bundles and bundles of ideas rushing up now and you are so ready to type them out one by one, but before you unleash your ideas, let me tell you our investigation finding first.
1) Scav. Manifold is filled 80% with FRESH WATER. Manifold position is below cylinder head, saying this is to let you know water must have come from cylinder head side, and not from the manifold to the head (water cannot flow anti gravity).
2) Thinking that water must be from T/C or Air cooler ? nah, T/C is water cooled but pressure test the casing no leaks (pressure test with hot water as well), air cooler is sea water cooled, also pressure tested no leaks.
3) Cylinder head - everyone knows water is from here, BUT ! pressure test the head, no leaks. Valves (suction / exhaust) seat rings are uncooled type. Injector sleeves are water cooled but no leaks from there during pressure test. Cooling water connector - 4 pcs per unit O-rings were badly squeezed and damaged though...HOWEVER, even the o-rings were the culprit, water will only leak OUT but not INTO combustion chamber, chamber is sealed with protruding land of cylinder head + cylinder head gasket (brass) !
4) Say if the sealing arrangement is compromised, then when engine runs, we should get a gas leak, but engine was running fine......with white smoke emitting though. I know I know, this is an indication of water leaking in but where does the water come from ?
God it kills so much of our brain cell, every time the top guys came in for root cause we cannot convince them, we were shot down by many questions which made our investigation look frail.
I need advise from you experts out there man, I really do, please provide constructive ones, rule out the sabotage part or the god factor, we are all technical guys and we require hard evidence to show those morons on the top...c'mon guys, help me out...