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From my sons KLX300R. Compression was low so we pulled the motor to rebuild. Initially we noticed right off the bat that the skirt on one side (a common sight for us 220 owners)had departed some time ago, likely before we took ownership last year as the oil has never shown signs of contamination that would have been there from grinding the skirt up in the gear box. Then we pulled the rings off and noticed the damage in the picture below. The piece that broke was the piston body between the upper two ring grooves. Never seen one break there before.

VENT, VENT, VENT...

I'll skip the fair analysis of the situation, but no need to bad mouth any part under the circumstances.

Strange to see a ring land break in a klx. Now if it was a late model turbo subaru that would be normal.

Good you cought it before it got really ugly.

Makes me wonder where the pieces went...

The ring land piece was still in place, held there by the rings and the cylinder. Thank goodness it was a 4T with no ports cut in the cylinder. The skirt I believe came off before we bought the bike. The PO had not well cared for it. Likely it was ground up in the gearbox. Have now split the cases and there is no indication of damage to the transmission or crank.

That is crazy that a previous owner would just keep running it. I guess we should never underestimate a previous owner. Wow.

That is a common failure spot on the 310 Jetski (supercharged 1.5 liter), wonder is they get those from the same piston supplier. That's an 18 yr old bike though, so it's probably irrelevant.