I had my top end coated by Swain Tech. PC-9 on the skirts, TBC on the Piston Heads, and Domes.
I had the same problem with mine. siezed during break in process. Out riding on gravel road. Let off the throttle and the back tires just lockup. So I snapped the clutch a few times to get it to free up. Then pulled over to let it cool. Started it up and putted back home. Pulled my cool head off. No scratches or marks that I could see.
Fast Forward 20 Hrs of run time later.
I decide to do a leak down test. Just because. It has been running fine but just to give me some confidance it is all sealed up. Do the leak down test and find a tiny leak under the LH Cylinder. So I tear it down and find this.
I am petty sure that it happend because it was a little on the tight side when I put the engine together. In the pic of the cylinder you can see just a tiny bit of aluminum transfered to the sleeve. That is the only damage that happned to the cylinders. The PC-9 is probably what helped save my cylinders. There isnt a scratch other than the little bit of aluminum.
RH Piston and Cylinder.
LH Piston (Same Side as TINY air leak)