2004 GTX Piston Explosion

[SkiHobby]

I'm rebuilding my 2004 GTX 185 SC and want to know if anyone has had a piston explode like you see in the picture below and if anyone knows what the cause may have been.
-Cylinder wall is not damaged.
-Rod is not bent

The way the piston disintegrated into so many smaller pieces seems pretty unusual.
Thanks

 

[Flightjunkie]

I'm rebuilding my 2004 GTX 185 SC and want to know if anyone has had a piston explode like you see in the picture below and if anyone knows what the cause may have been.
-Cylinder wall is not damaged.
-Rod is not bent

The way the piston disintegrated into so many smaller pieces seems pretty unusual.
Thanks

View attachment 52131

Hi.

Wow!

I'm new to these Jet skis but a skilled mechanic. When I see that in vehicle engines it's almost always on an engine with forced induction, and caused by detonation. The fuel explodes rather then burning. The shock loading can easily shatter the piston which is strong but brittle.

Vehicles have a knock sensor and the engine control module pulls ignition timing and or reduces boost when a knock is detected. Checking the codes shows "knock detected"

Some jet ski guys will have to chime in on if these skis have a knock sensor, if there would be a fault code sent, and what type of fail safes the control module implements when knock is detected to prevent damage.

Detonation could be cause by old gas, poor octane fuel, overheating engine, too high boost, too much ignition timing, and several other factors.

Sorry I'm not of more help. Good luck with the rebuild. Don't miss any metal pieces! Clean everything really good.

 

[nfdmedic]

2005 RXP same issue but it through rod through block and rod hit the starter. rebuilt last winter. Be sure to replace the screws holding the timing gear. I didnt and had a failure at 20 hrs blowing a head gasket and bending valves. working on it now.

 

[Flightjunkie]

2005 RXP same issue but it through rod through block and rod hit the starter. rebuilt last winter. Be sure to replace the screws holding the timing gear. I didnt and had a failure at 20 hrs blowing a head gasket and bending valves. working on it now.

Hi.

Wow! That could have punched a hole in the bottom of the boat! Looks like it's time for a new motor in that situation....

 

[SkiHobby]

Thanks for everyone's insights. It's weird how the piston disintegrated. Two valves were bent but the rod is still in good place. It seems the piston just got so hot that it broke apart. Have chunks in the oil filter and broke part of the inside of the crank case.

 

[GrinchMonster2000]

Can you post a picture of the other 2 pistons and heads.

 

[SkiHobby]

The other two pistons are still in the old head. They are hardly carboned. Here’s the only pic of the head.