It is easy to imagine the lubrication to be "permanent"
- good for more than the expected service life of the motor.
- say 10 or 15 years
No manufacturer (in their right mind) would expect people to be trying to run these things 60 years later.

I am presuming that the motor bearings are not on the regular maintenance because
- often hard/impossible to reach without disassembly
- dripping oil/grease is a mess

Ideas ???
-Ed Thelen

A Tale, added later

Long ago (maybe 2004) I was on a raid to a naval something, maybe Mare Island, with Grant Saviers.
He was securing cabinets and other material for the 1401 project, and his machine shop.
I came into possession of a beautiful 5" OD needle roller bearing. I kept it on my desk at work for several months for people to admire and play with. Then it disappeared :--((

Yes, most motor bearing grease has a definite service life. The oil evaporates over time leaving only the carrier goop and sometime thereafter the bearing fails. Noisy or spectacularly depending on how much horsepower. I saw a youtube re the failure of the roller bearing on an train coal car axle actually melting the 6" diameter axle.
Derailing resulted.

In contrast to the unique mag clutch bearings, it is very likely that any electric motor of the past 80 years uses standard ball bearings. McMaster has a big selection of "electric motor grade" bearings and if not in the catalog, Applied Industrial on Brokaw is where I went (ex King Bearing). The bearing should be marked as to size and type of seal. Or take one. Might be metric ID/OD or inch. Check with a caliper plus width.

Since this is a 3 phase motor there is no messing with start windings, capacitors, and switches.

This failure might be a good warning to cycle thru replacing bearings in all others. (a song I've preached b4).

Absolutely don't buy Chinese bearings on ebay or amazon.

Grant

I didn't answer part of Ed's question.

Smaller (up to 10 horsepower or so) motors most always have sealed (rubber lip seals) or shielded (metal "almost" seals). For motors, more are shielded since the bearings are reasonably well protected inside the motor and shielded generates less heat.

Both are permanently lubricated for life. I should note that most every bearing size has numerous options - class of fit, precision, type of grease, etc. However, only class may be a choice off the shelf. Old US were ABEC 1 (sloppy), ABEC 3 (motor grade), ABEC 5 rare (good precision) ABEC 7 or 9 (super precision). Price ratio 1 to 9 ~ 25x. ISO P5 is between ABEC 5 and 7, I just put new P5 spindle bearings in one of my lathes.

Very large motors generally have a grease fitting for periodic lubrication and the bearings don't have seals or shields. Grease needs to be applied sparingly so it doesn't go everywhere.

An emergency fix or for an unobtanium size for a bearing with hard dry grease (not wear), for a shielded bearing is to soak it in oil or better soak it in oil in a hard vacuum and try to get air pressure to force in some oil. A hypodermic needle/syringe can inject oil thru a rubber seal. Palliative care at best.

Reliable brands - Fafnir, NTN & NSK Japan, FAG, Timken, SKF, MRC, NACHI if you are searching on ebay. Only buy new, sealed in box. My P5 NSK tapered roller bearing finds were NOS $140 vs $400 from suppliers.

Grant