Originally I had asked about the single speed of the Oreck
Professional Air cleaner: Apparently NOT the bearings in the fan
motor, but the motor itself.

Turn on cold and the squirrel cage fan motor has three speeds. ANd,
runs quitely and well in the slowest speed. After running a while, the
motor starts generating a light grinding noise, and only has one
speed. Plus, and this is pure subjective, the motor metal body seems
hot.

If the fan can run well for a while, it seems it may be possible to
repair this motor.

It seems two possibilities, getting hot opens something up, or getting
hot shorts something out. Since the construction of the motor is a
transformer-like winding, it seems likely that after heating up, the
coil has a shorted turn.

Does anybody have experience with the death throes of such a motor?

Robert