2008 RMK 700 Piston problem

[KenF]

Good Day.
New guy, 1st post.

I picked up a low miles rebuild. 2008 RMK 700.
Popped off the head and saw this. The edge of the piston has two spots with a raised edge on the exhaust port. Left cylinder. SPX pistons. The right side has slight evidence of the same issue. Sounds like the seller is going to replace the Pistons.
But I'm wondering what would cause this.
Thanks guys?

 

[KenF]

 

[KenF]

 

[volcano buster]

I would inspect the power valve assembly real close. Apparently over time, the valve stem shoulder can hammer away at the bottom of the recess in the cylinder allowing it to lower the valve into the piston. I'm not sure if that is what you are seeing, but it wouldn't hurt to check. The cylinders may have to be sent in to get that cavity rebuilt which would keep the valve out of the piston in the future.