I am not sure that this is relevant to Roger's problem, but I once
decided to earth one of these motors, as being a "safe" thing to do.
Some time later, I went back to that area to adjust something, and
found that the motor was too hot to touch!

I un-earthed it, let it cool and all was well. Indeed, it is still
running happily 10 years later.

Best wishes
Nigel Perry

 [ Inside the motor is a short-circuit (fault) from the wiring to
 [ the case.  Not safe, not a happy situation.  :-(  -- Robbie