Originally Posted by funola

I took the shorted armature (on the right) to the rebuild shop for the owner to have a look. He had told me that it is very unusual for an armature to short out. He put it on his test set and applied voltage to the armature and slowly cranked up the juice till the meter moved and there was a spark. Sure enough it is shorted. He looked closely at the armature and pointed out the shiny 1/16" ring on the top and bottom of the core which can be seen in the pic. Apparently the worn bushing allowed the armature to rub on the field coil and this caused the core to deform enough to break through the insulation on the magnet wire and caused the short. I also wanted to buy a new bushing. When I asked "how much" he said "don't worry about it" and gave it to me.