Bikefreaks posting raised some questions in my mind about magnetic centers. Normally I think of motors with sleeve bearings when I think about magnetic centers, but do all electric motors have magnetic centers? If so then roller bearings could possibly be positioned (by manufacture or rebuild shop) in such a way that it could cause a pernmenant axial thrust on the bearing. This could result in premature bearing failure.

Eddie Ryan

A few thoughts:

1 - For antifriction bearings, the rotor position is set by OEM, not in the field during coupling to driven machine, so less potential for it to be set wrong.

2 - Magnetic axial centering force is fairly low, only a few hundred pounds for a machine 1000 hp. It shouldn't hurt anti-friction bearings. For sleeve bearings the axial force must be transmitted through a coupling and there is a possiblity of exciting a resonance of the flex coupling or fatiguing it.