How do you replace the bearings in a motor?

The puller set up in the second picture will do what you need , use the smallest separator then bolts to your puller. It won't hurt to use a bit of kroil on the shaft as you pull it. Bearings can bought lots of places Grainger , McMaster Carr , eBay . They are usually sealed bearings so most any of the shielded type in your size will work. Heating bearing may not be necessary , many times I find it easier to freeze the shaft overnight in a freezer . Usually the bearings drop on with light pressure. Then it's just putting it back together. Try not to rub any of the finish off the wound wires. Any dirt use a soft brush lightly clean what you can. If you have a brush run motor take care getting those in.
 
When it comes to pulling bearings, one single tool will not work every time. The good news, many folks who have a decently equipped shop can modify generic pullers to get the job done correctly. The ability to machine and weld will save you time and money. Using tricks such as freezing and heating also go a long way. Pressing in new bearings is IMO far easier than pulling old ones. That said, I have found using a die grinder equipped with a thin cutoff wheel to score an old bearing race (on the shaft) in two or three places followed by a few light strike will result in success in removing. Obvious precautions taken to protect unwanted contamination while grinding. Over time this has become a less frequent operation as the collection of home made tool, shims etc are kept for the next bearing job that might come up, but always an option.

As far as procedures on electric motors, I have only done a few Makita 4" grinders and smaller 2 hp or less sealed motors. On motors that I can't find information on, I start of by marking both ends with an indexing line for later reassembly. Remove the long screws and tap the shaft end cap with a small brass or soft hammer.Once it begins to move, Its pulled evenly off. Then the rotor assembly is pulled straight out slowly keeping track of any shims, spring washers etc. The inside of the motor can be cleaned out using low pressure air and electronic spray cleaner (air usually works well enough). Depending on bearing set back a pulley puller could do the job, but always soak the shaft with penetrating oil.
I recently replaced the bearings on a Rockwell/Delta finishing machine. This is how I proceeded.
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I had room to use a generic pulley puller for both bearings. This type of puller will damage the bearing being pulled out but who cares, they're already shot.
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Here you can see the indexing mark I mentioned on the rear end cap and housing as well as the shims and spring washers in the lower right. I should have mentioned the fan on the rear was removed prior to disassembly (snap ring).
The rotor assembly shown was in great shape for a 34 year old motor. The right end of the rotor is the rear and shows the centrifugal switch and was also inspected prior to installation of new bearings.
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The pressing operation went smooth and an old sleeve was used for this. The custom sleeve was turned long ago for a different job and lives in a bucket along with other pieces next to the press. The sleeve should slide freely on the shaft (OD) and contact the inner race of the new bearing only. I froze the bearing in a Zip-loc bag for 40-60 minutes prior to pressing. The bearings also had a small shim for them to seat agents once pressed (most of them will) but make sure they do prior to pulling old bearings. If no shoulder is found, then careful measurements should be taken to ensure proper depth of new bearings.
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Nothing fancy about the HF 20T press. Its the correct tooling that makes it work.
These quality bearings found on the shelf at a local bearing house. All the bearings on the machine where a shielded type except one. I replaced them all with Koyo sealed bearings to keep the grit out. These new motor bearings ran under $5 each so check your local sources. On the upper left, you can see the sleeve that was used to press the new bearings in.
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The inside of the motor after using low pressure air (40 psi) to clean out. Looks amazing considering its age.
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Reassembly of the rotor;
You must be carful not to contact the rotor to the stator and line up the bearings to the end caps with all the correct shims in place. I was lucky to have an extra set of hands for this. The end caps have bearing bosses that retain said shims. A light coat of dielectric grease helps keep them in place during assembly. Once you verified everything is lined up properly you can begin to tighten the long screws evenly in a criss-cross pattern pausing to gently tap around the end cap using a mallet or small dead blow until fully seated and spinning the shaft by hand (during the process) to ensure all is well. Reinstall rear fan and vented cover and bench test if you feel the need. We installed the motor and then tested. It runs like a new motor without the grumbling it once had. I also replaced the start capacitor for good measure.
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I hope this answers some questions and can be of help.

Turn and burn,
Paco

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Nels,
There's a lot of good information given here for you. One thing I didn't see mentioned is the importance of how the new bearings are driven or pressed into place. If the new bearing is being pressed or driven onto a shaft, drive ONLY on the inner bearing race. If a new bearing is being installed into the end bell (usually not the case) or a bearing housing, drive ONLY on the outer bearing race. For removal of the old bearings it doesn't make any difference as they are being disposed of.

Ted
 
The sleeve should slide freely on the shaft (OD) and contact the inner race of the new bearing only

Nels,
There's a lot of good information given here for you. One thing I didn't see mentioned is the importance of how the new bearings are driven or pressed into place. If the new bearing is being pressed or driven onto a shaft, drive ONLY on the inner bearing race. If a new bearing is being installed into the end bell (usually not the case) or a bearing housing, drive ONLY on the outer bearing race. For removal of the old bearings it doesn't make any difference as they are being disposed of.

Ted
Mentioned in post. This is very important!
 
You can probably use a piece of pipe to tap the new bearings in. Just make sure that it only hits on the inner race, as others have noted.
 
I've found that many standard pipe sizes make nearly perfect tooling for pressing metric size bearings like 6200 series for example.
A 1.25" piece fits the outer race perfectly without hitting the shield. Half inch piece for the inner race.
MS
 
When using a puller, put a protective cap over the end of the shaft so the center isn't damaged.
If the shaft has to be set up in the lathe, a bad center hole will make you crazy.
 
When using a puller, put a protective cap over the end of the shaft so the center isn't damaged.
If the shaft has to be set up in the lathe, a bad center hole will make you crazy.
Sometimes I'll take a hex nut like a 3/8 or 1/2 and put it between the center point of the puller and the end of the motor shaft to protect center in the end of the shaft.
I remember having to fix a center in the end of a motor shaft from a 75 HP DC motor before I could recut the commutator. The lathe I was on did not have a way to install a drill chuck in the tail stock or anyway to hold a drill chuck in the tool post. Had to grind a tool to go in and touch up and remove the dings at the front of the center. I was doing this on a 36" Monarch lathe with a make shift adapted steady rest!
 
4gsr
A messed up shaft center was one of my pet peeves. Had to deal with a number of them.
Terry Lingle already mentioned using a little never seize when installing bearings but I would like to add to that.
Too much never seize takes up space and can change the clearance of the bearing. It can also make a race seize to the shaft slightly crooked.
Small effects but they can cause problems or reduce bearing life.
Never seize applied too thick can also cause a bearing to score or gaule to the shaft on removal. Seen it!
I will put it only on the fit if the bearing is being heat shrunk. Most small bearings have only two tenths interference.
If pressing the bearing on I will put it on the shaft and race but in all cases its spread so "thin" you can hardly tell there's anything there.
 
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