One thought would be a bearing close to failure. Can you lube the
bushings/bearings? What is being driven by the motor? Could it be
external to the motor or is the motor freerunning when it happens?
Respectfully,
Ron Moore

"JimInsolo" wrote in message
link.net...
I have a 1 HP induction motor with capacitor start and capacitor run. As I
understand the function, the start capacitor circuit is engaged at start
up
and then dis-engages when the motor reaches full speed. The motor works
fine most of the time, but every so often it will make a terrible sort of
vibrating racket and blow the breaker. Sometimes if I just wait a minute
or
so it will start and run fine again. Any ideas on what could cause this?