Don't understand how a valve could break from water in the combustion 
chamber. The normal air/fuel mixture is compressible since it is a gas. 
If a liquid (in this case water, but in other engines could be fuel or 
lubricating oil (radial aircraft where it is standard practice to pull 
the prop blades by hand backwards to purge cylinders of liquid) gets in 
the combustion chamber, and the piston comes up in the compression 
stroke with both intake and exhaust valves closed, something has to 
give. This almost always happens when the engine is tried to start, and 
almost never a running engine, but I guess if water got in a running 
engine there would be damage. Basically what happens is the piston comes 
up, liquid being not compressible, usually the starter creating power, 
with inertia of the flywheel and other components, the following parts 
are prime candidates to break: broken/bent crankshaft and/or connecting 
rod, broken piston, crankcase or cylinder head. If the valve is open, 
the liquid can escape, if the valve is closed, it is supported by the 
valve seat in the cylinder head and there are no loads on the valve. I 
believe it is more likely the valve failed (is this engine known for 
"swallowed valves" ??) from fatigue. If the valve guides are loose 
(worn) then as the valve seats on the seat, the stem is allowed to 
wobble and the valve head (disc) contacts the seat at different spots 
along the perimeter and there is a stress reversal on the stem to head 
junction which causes fatigue. When the valve fails, the head comes off 
the stem, and may or may not breakup, likely pieces will jamb between 
the upcoming piston and cylinder head, usually rattling around there a 
bit causing much damage inside the combustion chamber including 
battering the spark plug along with breaking heads, crankcases, etc.

As I was writing above, I became more convinced, the valve failed first, 
the top of piston and inside of combustion chamber  will  show battering 
like the sparkplug.  Have them E-mail pictures of these surfaces (and 
you can send them on to me)! The engine has a programmable RPM limiter 
that they should have programmed as a rental unit to be conservative 
with RPM's so engine speed should not be an issue. The engine if 
overspeeded could float valves where the valve doesn't close quick 
enough and the piston strikes it bending the valve stem.

I have had an exhaust valve fail on a 320 cu. In. Lycoming aircraft 
engine while at 11,500' over Southeastern Georgia (USA) with 4000' thick 
clouds below. We made a successful dead engine landing at a small 
airport. It took 1/2 hour to figure out what had happened. We were 
fortunate that the valve broke up after banging around awhile, with the 
crankcase, cylinder, connecting rod and piston intact. The engine was 
not contaminated with debris, and we changed the cylinder (head is part 
of assembly) and were on our way in 2 days. When we got home we replaced 
all the other exhaust valves. With my familiarity of engines and what I 
learned, I can say the problem is not yours, and the water came after 
the valve failed.  Were there any unusually noises after it stopped 
first time.

Vitaliy wrote:
> Got an email earlier today from the shop owner:
>
> -->The damaged jetski is a 2006 Kawasaki STX-15F.  As you saw, there was 
> water in the engine and engine compartment which caused
> a valve to break ruining the cylinder head.
>
> A rough estimate to fix the broken cyinder head includes: parts  $3254, 15 
> hours of labor @ $40 per hour, misc. machine work $250.
>
> The estimate to put in a standard remanufactured engine includes:  Engine 
> $1795, Gasket Kit $86, Shipping $360.  Total: $2241
> These prices include my purchasing discount for the engine and gasket kit. 
> I am not charging you any labor hours or jetski down time which would total 
> approximately $500.  The place where I get the remanufactured parts from 
> said the engine would take 10 days to get.
>
> Please get back with me as soon as you can.  I would like to get the parts 
> ordered and this ski fixed as soon as possible.
> <---
>
> She didn't know exactly where the air intake is on this jet ski. I can ask 
> their main mechanic guy.
>
> Vitaliy 
>
>   
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