Long story short i bought a gp800r from a guy with a blown motor. He stated that he had an sbt engine installed a while back and it blew up. Now i have no idea why he did not go thru you guys to have it replaced but currently it is outside of warranty. I tor the engine down my self and found the front piston had the top ring completely gone and the pto piston had a huge chunk of the top ring missing. Upon further inspection it appears that both lower rings have spun under the ring land stop pins. I assume the top rings did the same and caught a port inside the cylinder which is what destroyed them. Click image for larger version. 

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To me it looks like the pistons may be defective. It looks like the ring stop pins(locator pins?) Are not drilled low enough into the ring land to prevent the rings from spinning under them. Every 2 stroke piston i have seen in person and on google images has had the pin drilled where at least the radius of the pin is in the ring land.

I was intending to purchase a new topend from you guys but this pin placement worries me. Could you give me any feedback?