sounds sorta like the same thing that happened to my tekno 1515 1y/f. it was temping fine after running two sets of 4s though it. take it out a few weeks later and I don't even finish off one set and the motor is cooking hot, like 180deg+
I take it home, hoping I didn't demag it. pulled the endbell off and pulled the rotor, which from the force needed to pull it out, I doubt it demag'd. Anyway further inspection revealed some blackening around the end of the heat shrink at the end of one of the phases. I cut it back a little and it looks like 1 or two of the wires shorted out.
