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Question on electric motor bearings

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John TV

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#1
So still consider myself as green as grass to this whole hobby and there are all kinds of new experiences I have never tried before.

I have a 5 hp. 3 phase motor that is the "idler" motor for my rotary phase converter. It was used when I put it into service and it is a Baldor "drip proof" type motor. I have used it very little and I am getting what I first thought was a harmonic high pitched whine (very anoying) after the motor runs for a minute or two. I now wonder if the bearings are starting to go since a pump of grease will make the sound go away for a while. I have just started to research the replacement of the bearings and here is where my question comes in. I have never ordered or repaced bearings before on anything other than a car or trailer. In my initial look up of the likely size, I am seeing a wide range of types, etc. Is there a thread here I have missed that is a primer on bearing info? Looks like I can spend between $10 and $240 per bearing? Needing some guidance on what level and supplier to use. I most likely will call Baldor and get their parts but it would be nice to have some knowledge before I make a decision. Thanks for your thoughts.

John in Minnesota
 

tq60

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#2
Just pull it apart and gm isit a local bearing supplier.

A 10 ish dollar part


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Ulma Doctor

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#3
Hi John,
bearings for modern electric motors are most likely measured in millimeters.
ABEC3 is a grade suitable for electric motor use in most instances, this being one of them
your 5 hp motor may have 6305ZZ bearings.
i would suggest using neoprene sealed bearings, as the seals generally make the bearing last longer
if your motor does in fact have 6305 bearings, the designating would be ABEC3 6305SS

here is a chart of bearing sizes
https://www.bearingworks.com/bearing-sizes/

SKF is a good name that's great quality
 

John TV

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#4
great info guys, thank you both.
 

Bob Korves

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Good input from Ulma Doctor. Sometimes SS (for double sealed, sealed on both faces of the bearing) in the bearing part number is changed to -2RS, which means the same thing as SS. The double sealed bearings work much better than double shielded (ZZ) at keeping dirt and grit out. In the old days when bearings were sealed with natural rubber, they would disintegrate at a young age, so double shielded became popular. Now, the seals will usually outlast the bearings, so they are the way to go until you get into really high speeds, then the lack of rubbing contact in the double shielded bearings might be more useful, the seals might overheat if they were used. ABEC3 bearings are appropriate for an A/C electric motor.
 

rock_breaker

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#6
As with most every thing these days I believe quality goes with price and the high price bearings are for use in high precision machines.
If you can get the bearing races out of the motor most bearing houses can identify them and cross reference them to different manufactures and perhaps price range. I did this with a drill press with good results.
Have a good day
Ray
 

John TV

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#7
Great info from you all. Now just need to find the time to pull the motor apart. This forum is so great at sharing and helping us new to the hobby. With the info I have learned here, I am much more confident in attempting to undertake new challenges. You tube is awesome too but here you get different opinions and options and the logic behind the options. You folks are fantastic, thank you.

John. Minnesota.


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fixit

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#8
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.
 

John TV

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Wow, had no idea, thank you. I will look for those bottom ports. Top is just grease zerk. Makes sense, just never used anything other than automotive greasing before. I love this forum!

John


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Ulma Doctor

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#10
not all motors have grease ports or grease plugs to remove,
most NEMA motors i work with don't have grease ports with removable plugs, just zerk fittings
 

Eddyde

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#11
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

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#12
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

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#13
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

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#14
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
 
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