had the motor/trans./carb. re-done. Ran for about 30min and the engine froze up. Upon tear-down noticed that cylinder bolts were less than hand tight and fuel mix may have been lean.
Cylinder was scoured and piston melted.
Re- bored with new piston, bolted up ran well. After riding around house for 30 continous minutes, same thing.. engine froze up. Any ideas what could be causing this?

Heat cycle it and retorque....
Try to run 5-10 min and ck
It should`nt be happening.

Good luck.

If I recall 12 lb pds. 144 inch pds......better ck that.

Oil injection failure?

I use pre-mix. one bottle of MCI to 4 gal of gas for break in. The motor/carb/tran was all done by the "expert" on lt 80's. He set the jetting for my elev. and on the second bore I went up 8 jet sizes just to be safe. Run 91 octane with 1qrt kemco/5 gal gas. Stock intake. The builder did the porting. I heat cycled the motor both times for break in. Froze up after 20+ min of riding both times. I'm lost and tired of dumping money in an old bike bike she will out grow in a yr. Arggghh.

Pilot jet or needle richened up? Maybe a bad ("new") crank seal??????????

can you get any pics of the damage ?

gotta see the damage. would be able to help a bit more

Heat cycle it ...
Ck cyl head torque...

Maybe rich up the pilot and raise the needle!!

Keep us posted.

Any in take boot leaks between carb and crank case ?

The "expert" from atvconnection?

That's got to be the reason, but I sure couldn't find one. I didn't check the first time... assumed the builder knew what he has doing.