Question on electric motor bearings

[Eddyde]

All good advice above, My $.02
Don't waste your money on the OEM "Baldor" bearings they'll probably be twice the cost. Just get stock bearings from a known brand, should be no more than $20 apiece.
Also, if you use double sealed bearings you won't ever need to grease them, they are lubreacted for life.

 

[John TV]

I know I am repeating myself but... I love this forum! Thanks guys.

I ran the mill and rotary phase converter for about half an hour yesterday and no annoying high pitched howl, maybe the bearings just needed a bit more grease? But my suspicion is that noise will be back shortly and a bearing replacement will be in order. With your help I feel much more confident I will be getting the appropriate bearings. Thanks again!


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[Downunder Bob]

Generally when you dismantle a motor you will find the bearings are fairly tight on the shaft but only a firm sliding fit in the housing end caps. Use a gear, wheel or bearing puller to remove the old bearings. be careful fitting the new bearings, please dont belt them on with a hammer. the best method is to warm them up gently, when I worked on the ships we always put them in a clean container covered in oil any light machine oil will do, and heated them up to about 120c 250f, with the shaft held vertically, the bearings should just drop on. If you have to press them on make sure you use a sleeve that only puts pressure on the inner race.

 

[tertiaryjim]

Most regreaseable motor bearings have plugs on top & bottom. The proper procedure is to remove both plugs, pump grease into top port toll it flushes out the old grease from the bottom. close ports. Forcing grease into one port only will not grease bearing, but force grease into the motor housing. Just the way I was taught during my 35 years as a maintenance supervisor.

Good procedure fixit.
I have replaced bearings on a number of motors which had zerks and were greased on a timed basis.
When I opened them up I found they had sealed bearings and the grease was just forced out the bottom or into the stater.
I like to use sealed bearings and remove the zerks.
There is usually one or more springs which press against the brng on the back of the motor. They are needed.

When using a puller make a plug to go between the motor shaft and puller screw so the motor shaft isn't damaged.
I've had to do machine work on a number of rotors which had the centers damaged and it took time to clean them up
and make them true to the shaft center.

If the brng has spun in the motor end cap and worn the sliding fit you may have to sleeve that fit.
Measure the bearing fits in the end caps cause now is the time to fix them.

These small motor bearings have only 2 tenths interference to the shaft.
If the shaft diameter is 1" then heating the bearing just 60deg above ambient will expand it 4 tenths.
It is best to not heat a sealed bearing above 120deg or the seal may be damaged.

Some people use a toaster oven or you can set that Christmas ham aside and use the big oven to heat the bearings.
As others have said, it's a good idea to freeze the shaft.
Also, when installing the bearing I try to have the shaft solidly standing vertically if possible.
I also like to rub antiseeze inside the bearing and on the bearing fit. You can thin the antiseeze with a light oil.
It has to be spread so thin that that it's almost invisible as it it will take up space and change the brng fit.
Antiseeze will make the bearing easy to pull next time if it's applied really, really, thin.

Many of these motors have a inner shield that has to be placed on the rotor "before" seating the new brng.
Big mistake if you forget those.

The brng must be held firmly against the shoulder of the shaft until it has seated so you'll need a insulator
for your hand.

I've rambled on till it's embarrassing. Hope some of this helps.
Jim

 

[martik777]

This is my Lincoln electric 3 phase 1HP motor. There is a grease fitting which looked like it was recently used but no exit hole. The hole on the back side does not go to the bearing. It runs quiet and does not heat up at all so I think I should just leave it. If I grease it with some incompatible grease it could reduce the lubrication?

 

[Downunder Bob]

Generally when you dismantle a motor you will find the bearings are fairly tight on the shaft but only a firm sliding fit in the housing end caps. Use a gear, wheel or bearing puller to remove the old bearings. be careful fitting the new bearings, please dont belt them on with a hammer. the best method is to warm them up gently, when I worked on the ships we always put them in a clean container covered in oil any light machine oil will do, and heated them up to about 120c 250f, with the shaft held vertically, the bearings should just drop on. If you have to press them on make sure you use a sleeve that only puts pressure on the inner race.

Additional info. On the ships it was standard practice to replace electric motor bearings every 5 years. Most motors have a fixed bearing at one end and a sliding bearing at the other end this is to allow for thermal expansion.

Some motors will allow bearings at both ends to slide and be held in position with light wave springs behind each bearing this allows the rotor to find its own magnetic or electrical center and will be more efficient and run cooler and quieter, with these motors it is important to re-assemble exactly as before don't mix things around.

We also found the most modern motors did not have provision for greasing and were fitted with sealed bearings. I don't ever recall one of these failing within the 5 years. Not bad considering they ran 24/7.

The earlier comment about greasing with a drain hole to allow old grease to escape is very true. be very wary about greasing a bearing that doesn't have the drain hole.