That sucks.
You put a lot of effort in and did a great job. :wink:
I'm no expert but to me it
seems obvious. The piston siezed, likely due to lack of oil. On an ancient bike I also don't trust the oil injector pump.
The crank pulled the piston pin out with the skirt in the process. This relieved the 'stiction' and when the motor cooled it no longer appeared siezed. :idea:
Have it bored to the next size, run premix, get a new piston and rings and if there's no lower end damage (should be fine) you're good to go.
