This 125 belongs to one of my regular customers. Over the last year, I have installed a new clutch, trued wheels, replaced fork seals, re-packed the silencer, etc. Recently the owner had accidentally put non-mixed fuel in the tank and ran it for a while.
The pictures show the galling of the piston and the cylinder. This may have been caused by the non-mixed fuel. I removed the seat, tank, exhaust, and radiators to access the cylinder. I then removed the cylinder. The crank has some minimal side-to-side play but has no vertical play, so we are going to send the cylinder off to Millennium Technologies for repair and also replace the piston, ring, and wristpin.
Update 3/8/12: I finally added some more pics of the bike going back together. I powder coated a few parts for some added bling. The owner of the bike TJ Maher, went on to take a win at the WNC ag center that weekend.