what caused it?

[Mile9c1]

Updated pictures:

I think it was lack of lube. We switched the ski to premix and it seems to run fine. It was a WRIII, so I doubt it injested water.

 

[Crab]

My wetjet motor looked the same, Watcon took one look and said oil pump failed.

 

[Kennay]

Air leak?

 

[Mile9c1]

My wetjet motor looked the same, Watcon took one look and said oil pump failed.

It definitely looks like a lack of lubrication, it's just strange that the front piston is fine. The oil enters at the top of the carb.

 

[DAG]

was compression even across the holes

 

[willycrumb]

duh da duh.

 

[Mile9c1]

was compression even across the holes

No, the front was at 150psi, the rear was around 130psi.

 

[Shonuff]

Looks like water ingestion or no lube.


http://server1.sbtontheweb.com/forum/showthread.php?t=298

 

[strictlystandups]

looks like your rings failed, (well obviously) causing excessive blow by heating the sides of you pistons allowing hot combustion gases to leak past the rings. how does that cylinder look and are there linear scratches all the way around on both piston and cylinder? I would also have to say that at some point you had a lubrication failure maybe just an intermittent one that was enough to cause that sort of damage.