2003 bf 225 broken #6 piston

Been working on my motor for a couple of weekends now.Finally pulled the port head off because of low compression in the #6 cylinder. found about a 1 inch piece of the piston missing on the right edge right down to the first ring.seems like the aluminum pieces are imbedded into the top of the piston and the piston is real white where it broke.I am trying to figure out how this happened and want to correct the problem before putting the motor back together.Called Honda about service bulletin #56 with not much success. They told me they would not warranty a 9 year old motor.So far I am leaning toward the exhaust tubes sucking water into the cylinder or maybe the injector is not working correctly and leaned out the cylinder. Any thoughts what could have caused this damage? My next step will be to pull the crankcase cover off to get to rods and crank to remove the piston any suggestions here would be greatly appreciated , thanks Rob.

There are several reasons, but if I understand your failure correctly then the ring land has broken? Early models had piston/rings that were allowed to rotate. This design was linked to some short engine failures. Different pistons and rings came out a couple year's later. But then there is " ole man detonation" who is relentless in the destruction of high compression engines. Caused by poor quality fuel. Then there is pre ignition where the piston typically burns a hole in the center or on the exhaust side. Several factors contribute to this including the unit being over propped or the piston being being over heated by stuck or coked rings. Thanks Martin

The first thing I would want to check with this type of failure is timing. Was the engine still in time?

Another possibility, as you implied. If the exhaust tubes were not changed out IAW service bulletin #56 it is possible that water was injested in #6, and the rapid change in temperature cracked the piston. Either way, it looks like you are in for a major rebuild.