Motor bearings... repair or replace.   11-17-99

New and replacement sleeve bearings in small DC motors are impregnated
with "oil" and shouldn't be lubed. When working with old ones, I use
Molytone grease for capstan motors, computer PS fan motors, etc. In the
case of capstan motor repairs vs replacement, I use the condition of the
rotor shaft to help make the decision. Pull the rotor. If it's scored,
replace it and the bearings. I've had a bit of luck polishing out the
ridges on the shaft with very fine grit sandpaper (crocus cloth), but only
on my own machines, and as a last resort to get it going again. If it's
just discolored from being overheated, it's a judgement call. I usually
inform the customer and go with washing out the old lube with solvent on a
Q-tip (with most of the head removed) and "greasing" it with Moly. I've
been using Moly for nearly a decade and never had a callback for a motor
problem. Just oiling old bearings will not last. Factory lube gets like
honey, then siezes up. That's why it's important to wash it out. Some
capstans have two different bearings, a roller type on the bottom and
sleeve on top. In my opinion, it should be the other way around since the
top bearing takes most of the load with the pinch roller pressed against
it. The sleeve bearings are the ones that need the new lube.

Ray Carlsen
CARLSEN ELECTRONICS... a leader in trailing-edge technology.