One piston has 216 hours the other 4

[Boyd12]

The piston on the left came out of a 951 Di with 216 hours on it. The one on the left has 4 hours on it. It looks like water got in it. Any ideas?

 

[Boyd12]

 

[mikidymac]

We need more details.

Were the cylinders bored?
Who did the machine work?

Why were the factory ones changed?

Brand of pistons?

 

[Boyd12]

Apologies for the lack of details.
The left piston is a stock SD 951 Di with 216 hours on it.
The right one is a 951 carbed WSM platinum 1.0 over installed as part of a total rebuild. I dont know at the moment who did the machine shop work, but pistons/cylinder were installed by a company that is well known by PWC owners.
I am surprised by both of them. The Di had the crap run out of it (whenever the owner was in a wake zone, he was at full throttle, all day long.) by the owner who did no maintenance and said "oil is oil". It had mineral, synthetic and mixtures of both in it. This piston is in stupendous condition.
The one on the right (the other piston is the same) looks like it got some water on it.
My question is do you or anyone else think this was caused by water in the combustion chamber or something else?

 

[mikidymac]

It’s hard to say. A 951 can easily ingest water and cause that but it is just as likely from running lean due to poor fuel system maintenance.

 

[Boyd12]

If it was a old, unmaintained boat, I would totally agree. It has new fuel hoses, rebuilt carbs, Mikuni parts, no water in the hull. It is a mystery.