"anon" wrote in
ng.com:

Han,

I've never seen a bad bearing in these small motors cause a fire, but
I suppose it is possible. The usual risk from hot bearings is thermal
breakdown of insulators within the motor windings and wires, possible
causing a electrical hazard.

If the bearings races or ball are pitted (not that you can see them
without destroying the the bearing set), replacing the bearings is a
very good solution for that type of motor. They will be ball bearing
sets, not sleeve bearings. When you get the replacements try to get
the "ZZ" type which have both sides sealed, as your device is
apparently used in a dusty environment.

Sometimes you get lucky and the bearings stay on the rotor which makes
them easier to remove using a bearing puller. A bearing press is
handy for reinstallation but I've also used a heavy drill press (off)
with makeshift jig. Brinelling is a risk when approaching these with
a hammer, especially if the fit is tight.

Light machine oil was suggested for a temporary fix, and it indeed can
prolong the life of the bearings considerably if they've simply dried
out, if you can get the oil into the bearing set casing. However,
there is a popular canned spray that should be avoided, marketed as a
"lubricant" and is often touted as the fix-all for everything.
However, around sealed, greased bearings, the stuff is a nightmare
since it is a powerful degreaser, which liquifies the packed grease.
It's name begins with WD - don't fall for the hype.

Check for loose mounting as suggested since the cage is fairly
lightweight and would squeak if given the chance.

(The opinions and suggestion expressed above are my own and do not
reflect current enginieering or electrical standards in any way.)
Scott in Dunedin, FL

This is very close to a post-mortem, as predicted by Puckdropper.

I took things apart. This is a 7.7 Amp motor for 1050 rpm. It was
rather solidly mounted, so that wasn't the problem.

It was an interesting experience. There was 1 loose long bolt that
attached a grounding wire between outer housing and motor itself. If
there ever was a nut on the other side it is now lost. I can't get the
bearing covers (?) off unless I go out and buy something. So I am going
to ask a plumber friend whether he might know of a squirrelcage fan and
motor that is looking for a new home. Otherwise, I may just go and get
another one on eBay.

--
Best regards
Han
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