The bearings of an electric motor are normally removed using a bearing puller. It has jaws to grab the back of the bearing and the threaded rod of the puller mounted at the end of the shaft. When tightened, the bearing got pulled out of the bearing journal
There are times when you face the task of removing and changing the bearing of a motor but either your puller won’t fit or you just don’t have it.
There are other ways to do it and here are some of them.
1. Using a vise and a pair of pry bar
2.. Cutting the outer race and then applying heat to the inner race of the bearing
3. Using a bearing splitter
4. Using the lathe machine and its coolant
I. Removing a rotor bearing using a vise and a pair of pry bar
This method of removing the bearing is fast but it is necessary that the vise is securely mounted on a workbench. .
a) Clamp the rotor in a vise. Align the edge of the vice jaw to the rotor bearing.
Aligning the rotor bearing on the vise jaw
b) For small bearings sizes 6203, 6202, 6201 or smaller, you can use a pair of longer, flat tipped screwdrivers, with the same length if possible. For bigger bearings sizes 6204 and 6206, a pair of pry bars are appropriate.
c) If the shaft is rusty, polish it up first using emery cloth then spray it with lubricant.
d) Pry the bearing out.
Some rotors have an internal fan made of aluminum, and the bearing is right behind it. Mount the rotor on the vise in a way that the fins of the fan are butting on the vise jaw to avoid damaging the fan. Pry the bearing out
Prying out the bearing of a rotor mounted on a vise
II. Removing the bearing by cutting the outer race then applying heat to the inner race.
There are cases where removing a bearing is not possible with a puller like when there is no room for the puller jaw or prying it out can be challenging when the bearing is beside a flimsy fan. Heating the bearing will be your option
Bearings have an inner race which is tightly fitted in the shaft and an outer race that spins. Steel expands when heated so if the bearing inner race is hot and the shaft is cold it just slides out.
The heating process has to be fast otherwise the shaft will also heat up and both of them will expand. The bearing then will still be tightly held in place on the shaft.
In this case, you have to redo the process by cooling down the whole rotor first and then try heating the bearing again.
Procedure of removing a bearing using heat.
a) Secure the rotor in a vise
b) Using a thin disk grinder, cut the outer race of the bearing in two places until it falls off together with the balls. For smaller bearings you can use a Dremel tool.
On bigger bearings, you can use a cutting torch but make sure to cut it off to the side so that the molten metal will not fall on the shaft.
c) Let the rotor and the bearing inner race cools down. Put a fan.
d) Using a torch, heat the bearing inner race. You can use either oxyacetylene torch or a portable MAPP torch.
e) With your Kevlar heat resistant gloves on, pull the bearing out otherwise use a small piece of metal to gently slide the bearing inner race out of the shaft.
f) On bigger bearings, if you position the rotor upside down, the bearing inner race will probably just fall off.
III. Removing the bearing from the shaft using a bearing splitter plate.
One advantage of a bearing splitter is that you can remove bearings fast. I can tell you that because I use the arbor press instead of the puller attachment that sometimes comes with the splitter.
If you have an arbor press and a bearing splitter plate, you can literally remove a bearing in less than 10 seconds. That fast.
Second advantage of it is that if the bearing is too close to the fan that even a puller jaw won’t fit.
Splitter plate can be thin enough to fit behind those bearings.
The third advantage is when the bearing to be removed is fairly new and needs to be reused.
For example, a brand new bearing was installed only to realize that a snap ring has to go behind it. It has to be removed and the snap ring installed first before the bearing.
Normally, since the bearing is cheap we just replace it with a new one. Besides, when you use the puller, the seal gets damaged.
Not so with the bearing splitter. Its flat surface puts even pressure on the inner and outer race of the bearing. Although replacing it is still ideal.
Procedure in using a bearing splitter and a press to remove rotor bearings
a. Loosen the splitter bolt nuts until the splitter plate clears the diameter of the bearing.
b. Set the bearing splitter flat side up on the arbor press base.
c. Position the bearing on the splitter
d. With one hand on the arbor press’s lever arm and the other holding the rotor, press the bearing out of the shaft.
The process can also be made faster by keeping those nuts loose. In this way, you can easily position the bearing on the splitter, close the two plates together, and press the bearing out.
Another suggestion is to put a spacer between the rotor shaft and the arbor press ram shaft so that the position of the arbor press lever is at the ideal spot where you can get a good leverage
The disadvantage is that you need two people to remove bearings on a bigger rotor because of its weight.
Also, some arbor press designs are not suited for this purpose. The base should have an opening that can accommodate the diameter of the rotor.
Pressing out the bearing using a bearing splitter mounted on an arbor press
If a motor repair shop does a lot of rotor bearing replacements, modifying the base of the arbor press can be functional and productive.
For DIYers who don’t have an arbor press, setting the splitter on two blocks of wood and tapping the shaft with a rubber mallet to remove the bearing will also work.
IV. Removing the bearing from the shaft using heat and lathe coolant.
Removing the bearing stuck in the rotor shaft using a puller and oxyacetylene torch can be challenging if the bearing journal is already damaged, corroded, or oversized.
Bearing balls can also collapse making a puller useless or in cases where the outer race of a roller bearing comes off leaving the inner race on the shaft.
Heating the bearing inner race evenly white rotating and making use of the lathe coolant is one option.
Also, when you have to set the rotor on the lathe to measure the shaft runout, might as well remove the bearing there.
Procedure in removing stubborn bearing out of a rotor shaft
a. Cut the bearing outer race using a cutoff disk grinder or oxy-acetylene cutting torch if not out already.
b. Set up the rotor on the lathe.
c. Set the lathe speed to around 45 RPM and let it run.
d. Turn on the lathe machine coolant and point the hose tip to the rotor shaft about an inch and a half (3.8 cm.) away from the bearing inner race.
e. Heat the bearing inner race using the rosebud tip of an oxyacetylene torch.
f. When the bearing comes hot, you can just slide it out.
Removing bearing inner race using lathe machine coolant and oxyacetylene torch
There are other practical ways for sure that other motor mechanics use to remove bearings without a puller
If you have a problem with your electric motor or you want me to post a particular subject about it, please write it on the comment section and I’ll be happy to post it for you.
If you have other ideas, please share them below in the comments section so that others may benefit from it. I’m sure there’s a lot more ways to remove a bearing from the shaft besides a puller.
Electric motors are used to run machinery, pumps, compressors, blower fans, and all other kinds of equipment. Without motors, none of these machines will move.
The shafts of the electric motors are coupled to these machines using some kind of attachment. It could be a sheave (pulley), a coupling, or a mounted gear.
When electric motors are up for repair, it has to be disassembled and parts that are defective need to be repaired.
The end bell also called the end shield or end cap of the motor cannot be removed and bearing housing inspected if there is something attached to the shaft.
This post includes:
Steps on how to remove gear from electric motor shaft
Steps on how to remove a sheave (pulley) from an electric motor shaft
Tips on how to remove a coupling from an electric motor shaft
Tools you need to remove gear, coupling, and sheave (pulley). What to do if you don’t have them.
7 Steps on how to remove gear from The electric motor shaft
Electric motor shafts with helical gears are used on conveyor motors, roller motors, and gearbox motors while spur gears are commonly used on the motor as a spline for its brake or clutch.
Spur gear on the shaft used as spline for electric motor brake
Here are the steps:
Before removing gear from the motor shaft, measure the distance of the gear to the end of the shaft. This is so that you can reinstall it back at the same position later. Not unless it rests on a shoulder and/or a snap ring.
Check and remove anything that holds the gear to the shaft like a set screw or a snap ring. Sometimes a snap ring covered with grease is hard to see.
Helical gear held by a snap ring on an electric motor shaft
3. To remove gear from the shaft, use a two-jaw or a three-jaw puller.
4. When a gear is tight that the jaw keeps on disengaging, use a chain grip. This will keep the puller engaged.
5. Another way is to use a bearing separator and a bar-type puller. Position the bearing separator behind the gear, screw in the threaded rods of the puller, and remove the gear.
Electric motor gear removal using a puller
To remove a gear without a puller, use the rosebud tip of an oxyacetylene torch and heat the gear. As soon as it is hot, lightly tap it out.
Use leather gloves and a face shield when using oxyacetylene
You can also use an arbor press if you are working on a small motor and the diameter of the end bell will fit the press. Put a bearing separator behind the gear and press the gear out using the press.
Removing a sheave (pulley) from the electric motor shaft
Sheave held on to the shaft using a key and bolt with washer
Some machines are coupled to the motor using v-belts and at times flat belts.
Sheave (pulley) is installed to the shaft either directly or through a hub or bushing.
Electric motor sheave pulley with a bushing Is a two-part assembly. Pulley is first unbolted and removed from the bushing then the bushing is removed from the shaft.
Some pulleys have no bushing. It is only held to the shaft by a key and two set screws
This is how to remove pulley or sheave from the electric motor shaft:
1. Before removing the sheave pulley from the motor shaft, measure its distance to the end of the shaft. This is so that you can reinstall it back at the same position later
2. If it is held by a bushing, measure the face of the bushing to the end of the shaft.
3. Check for set screws and remove them.
4. Pulley is usually bolted onto the bushing using four bolts. It also has two threaded holes to accommodate the jacking bolts for easy removal of the pulley. Remove the bolts.
5. Spray the pulley, the bushing, and the shaft with an oil lubricant.
6. If the shaft is rusty, use an emery cloth or sandpaper to remove and clean the shaft.
7. Get two from the bolts that you have removed, and install them on the two threaded holes on the sheave pulley. If the bolts are short, replace them with longer ones. Use this as jacking bolts
8. Tighten these two bolts to remove the pulley. The bushing is tapered, so the pulley should just pop out.
9. The bushing has a sliding fit to the shaft but because of corrosion and the key, it could be tight. One way of removing it is by the puller.
10. Another way of removing it is by jamming a screwdriver on the split of the bushing. This will allow for the bushing to increase its diameter for easy removal from the shaft. For pulleys that do not have bushing, use either a two-jaw or three-jaw puller to remove it.
11. Do not grab it by the pulley groove or you will break it. Some pulleys have bolt holes to accommodate the puller.
12. For pulleys that don’t have bushing, you can also use a bearing splitter and position it behind the pulley. Put the puller jaw behind the splitter to remove the pulley.
13. If that doesn’t work, use heat. Heat the pulley using the rosebud tip of oxyacetylene and soon as the pulley is hot, it should just slide out of the shaft. Be cautious, it’s hot.
5 tips on how to remove a coupling from an electric motor shaft
Shaft jaw coupling held by a key and set screws
1. Before removing the coupling from the motor shaft, measure its distance to the end of the shaft. This is so that you can reinstall it back at the same position later. The coupling could be flush to the end of the shaft, out, or in by a certain distance. Make sure you take note of the position or have a picture.
2. Check for set screws and remove them
3. Use a puller to remove the coupling.
A shaft flange coupling with a key and set screws (not shown)
4. Most couplings are a tight fit. If you’re having a hard time with the puller, combine it with heat. While the puller is engaged, heat the coupling using the rosebud tip of the oxyacetylene and soon as the temperature reaches about 300C, continue pulling it out with the puller
Most electric motors have an external fan. It’s a way of cooling the motor, especially the enclosed motor with no air vents.
The term is TEFC which stands for totally enclosed fan cooled motors.
Not unlike the bigger U-frame of older motors, nowadays, they are compact.
The same horsepower motors are built in smaller frames and even designed for higher efficiency. The result is they run warmer that is why they have a cooling fan
Besides external cooling fans, some motors of Baldor and Toshiba have internal cooling fans. These fans are meant to directly cool down the windings inside the motor.
Internal fan of an electric motor
Fans are commonly made of plastic although they can also be made of aluminum or cast iron.
They are also held in the shaft several ways. Some are set screws, some are clamps, and some by using a snap ring.
Fan with integrated clamp and tightening screw
For example, Siemens uses a built-in plastic tab to lock the fan in place. You have to insert in this tab a strip of thin metal and the fan can be pried out easily.
10 tips on removing the fan of an electric motor.
1. Take note also how far the fan is from the end of the shaft so you can put it back the same way
2. Small plastic fans are usually held in place either by a snap ring or a clamp. Remove it and spray the shaft with a lubricant
3. Pry the fan out making sure that the tip of the pry bar is as close as possible to the base of the fan closest to the shaft. This is to avoid breaking the fan.
4. If the fan is too close to the end bell (end shield) and the pry bar won’t fit, use two long screwdrivers with a flat tip.
Image of fan too close to the motor end bell
5. If it’s so close to the end bell that even a screwdriver won’t fit, try these three methods:
.
Method 1
Remove all the end bell bolts
Get a center punch or any steel drift smaller in diameter and put it at the center of the shaft where the fan is.
Image showing how to remove the rotor and the fan by driving a center punch in the middle of the shaft
Using a mallet and the center punch, drive the shaft going to the opposite end until the fan comes out.
Do not let the rotor fall off the table
Method 2
Remove the end bell (end shield) that doesn’t have the fan.
Separate the rotor with the fan still attached from the stator.
Use an arbor press to remove the end bell and the fan at the same time.
Image showing shaft being pressed out using arbor press to remove the fan
If there’s no arbor press, use blocks of wood, center punch, and a hammer.
Put the end bell fan side up on the blocks of wood with the shaft above ground.
Have someone support the rotor while tapping the rotor shaft out of the end bell and the fan.
Method 3
With the fan still on the shaft, separate the end bell from the stator, by tapping the drive end shaft.
Using a three-jaw puller, remove the end bell out, dragging the fan out with it.
6. As I mentioned some Siemens motors have a tab locking the fan through the groove on the shaft. Insert two thin strips of metal on those tabs and the fan can then be pried out.
Electric motor fan with locking tab
7. Bigger plastic fans are held in place by a clamp. Loosen it up by unscrewing the bolts. Some clamps need a pair of pliers to remove and some have screws.
8. Again, pry out the plastic fan using two pry bars keeping the tip of the pry bars as close as possible to the base of the fan closest to the shaft to avoid damaging it.
9. Some plastic fans have openings to accommodate a small puller. Use the puller to remove the fan although setting it up takes a bit longer compared to just prying. Don’t forget to spray it with lubricant.
10. Bearing separator also works by placing it behind the fan then use the puller to remove the fan.
6 steps in removing the aluminum fan from an electric motor shaft
Most of the time you need heat to remove aluminum fans from the electric motor shaft. This is how you do it.
1. Remove the set screws holding the fan to the shaft.
2. Spray the shaft with lubricant and remove visible rust and corrosion from the shaft using emery cloth
3. Try and pry the fan out first. If it doesn’t want to go, use a puller
4. Sometimes there are openings to accommodate a small two-jaw- puller or bolt holes to bolt the puller jaws to the fan. It is not advisable to use the puller jaw on the outside diameter of the fan. You’ll break it.
Holes are provided on some fans to accommodate 2-jaw bearing puller
5. You can also use heat. Using either oxy-acetylene or a propane torch, heat the base of the fan. Do not heat the shaft. The idea is to expand the fan bore with heat while the shaft is cold.
6. Pry the fan out.
how to Remove a cast iron fan of larger motors
Most larger motors 100 horsepower and up have cast iron fans. To remove them,
1. Totally remove the bolt on the hub of the fan. Remove also the snap ring if there is any.
2. Most cast iron fans have a split hub. Insert a flat screwdriver on the split
Electric motor fan with a split hub
3. Insert and gently tap the screwdriver in the hub split until the fan loosens out
4. Pry the fan out. .
9 steps in removing a blower fan from the shaft of electric motors
Blower fans are easy to install when brand new. The set screws when tightened during installation sometimes create a nick on the shaft making it hard to remove
Blower fans are also ignored like it’s a maintenance-free unit. They’re not. They have to be maintained.
A Blower fan of an electric motor
Fan accumulated with dirt caused it to be out of balance. They will then vibrate, create noise, damage the bearings, and the fan hub, making it hard to remove from the shaft.
To remove blower fans from the electric motor shaft, you are to remove the two set screws then the fan slides out. Supposed to be easy, but the older it gets, removing it becomes a challenge due to wear and corrosion.
Do the following suggestions in removing blower fans;
1. Remove the two set screws holding the fan.
2. Spray the shaft to fan fit with lubricating oil.
3. Gently pry the fan out. If there is no room, you can use two L-shaped pry bars to remove the fan. Avoid deforming it.
4. Another way of removing it is to drive the shaft out going the opposite way using a center punch. But before doing this, make sure that the bearing has no retaining cap or a bearing cap. Skip this if your motor has it.
5. First, remove all the bolts on the end bell opposite the blower fan.
6. Using a mallet and center punch, drive the DE shaft out of the stator. The process will at the same time separate the rotor from the stator, the end bell, and the fan.
7. Sometimes you can use a puller. Fans have bolt holes to accommodate a two-jaw-bearing puller. To keep the puller from disengaging, install a locking chain grip.
Image showing a blower fan removed by a 2 -jaw puller
8. Another option is to use a three-jaw bearing puller, although there is no guarantee that the fan will not break or deform. Remember to position the jaw to the outermost part of the blower fan and a smaller puller cannot do that so use the proper size of puller for the job.
9. If it doesn’t want to go, heat the base of the fan first using oxy-acetylene or propane torch to loosen it from the shaft then try to remove the fan again. Do it slowly.
Removing the fan blades of an electric fan
Fan blades of an electric fan are held in place by a knob with a left-hand thread. This is designed to be that way for safety reasons.
As the fan rotates clockwise, the inertia tends to spin the knob counterclockwise which tightens it and does not loosen out.
1. Unplug the fan.
2. Loosen the clips and remove the front fan guard
3. With one hand holding the fan blades, loosen the locking knob going clockwise
4. Remove the fan
Removing the fan of a bathroom exhaust fan
It is a smart idea to regularly clean bathroom fans. Dust combined with humidity makes it out of balance resulting in noise and vibration shortening its life..
1. Pull down the fan cover. You might have to pry it a bit with a flat screwdriver so you could have a good grip.
2. Press together the clip holding the fan cover to release it from the unit.
3. Using a thin flat screwdriver, pry out the locking tab holding the fan from the motor shaft. Don’t lose it.
Conclusion:
These procedures are not concise because every situation is different.
In a motor shop setting, removing a fan is maybe easy because you have all the tools and equipment to use.
If you are in a place where the right tools are scarce, it may be challenging.
Different kinds and sizes of fans in different situations. Each have their own problems and difficulties.
Motor technicians have their tools, equipment, experience, and even colleagues to run to if they have difficulties. Some people don’t have those.
If you are encountering some difficulties or just have a question, we might be able to help.
Analyzing electric motor test results, monitoring its temperature, and noise level is just a glimpse of what maybe is going on inside a motor. But nothing is more conclusive than to see the inside of the motor and do all the inspections, measurements, and tests.
Disassembling an electric motor is not rocket science. With some basic tools, knowledge, and a safe work ethic, you can do it yourself.
A professional motor technician can disassemble a motor fast but that’s because they have done it a million times. A beginner can disassemble the same motor slower but who cares as long as it is done right and the purpose is accomplished.
These are the steps in removing the rotor from the stator. Each will also be explained.
If possible, test the motor first. This includes coil resistance, insulation resistance to ground, and test running the motor.
If you have a dial indicator, measure the runout and end play of the shaft.
Inspect the motor. Check for missing, loose, or broken parts.
Remove any shaft attachment
Remove the fan cover and the fan.
Mark the end bell orientation so you can put it back the same way.
Remove all the bolts fastening the end bells (end shield) to the stator
Remove all bearing cap bolts from the end bells (end shield)
If both end bells have back cap bolts remove the non-drive end (NDE) back cap bolts first
Remove the NDE end bell.
Remove the DE end bell and the rotor
Whether you want to replace the bearing, lubricate, investigate why it stalled or noisy, swap parts, or just want to see if it’s something you can fix, following these procedures in disassembling the motor will make your life easier.
In addition, I also included topics like;
8 ways to remove an end bell from the electric motor housing
5 steps in removing the rotor of an electric motor with a bearing retaining snap ring
11 steps to remove the rotor and end bell of a capacitor start single phase motor
13 steps to remove the rotor and end bell of a three-phase motor
9 steps in removing a heavier rotor out of the stator of an electric motor
1. Test the motor
When a motor arrives in a repair shop, the first question a technician asks is, is the motor grounded?
If you own the motor, you know what’s going on with it and your intentions of doing,
The bearings might be noisy, smoke came out of the motor, or the shaft of the motor seized, that’s why you are taking the motor apart.
In this case, testing the motor might be optional especially if you don’t have the necessary meters. Although it is better to have these test values for your record in case you have to replace it with a new one or you end up rewinding it.
Megger between the leads and the unpainted part of the motor. The reading should be ‘infinity’ if your meter is analog and 2 megohms or higher if it’s digital. If the reading is 1 megohm or lower, you might have some issues with the windings of the motor.
Measure the resistance between T1 & T2, T2 &T3, and T1&T3. The three readings should fairly be the same.
If your motor is a single-phase, the measured resistance between T1 & T4 must be lower than what you measured at T5 & T8.
2. Measure the runout and end play of the motor shaft
Runout is the movement of an electric motor shaft away from the true axis of rotation mainly due to a bent shaft or badly worn out bearing journal and/or housing.
End play is the amount of axial movement allowed by the motor’s construction to compensate for the thermal expansion of the shaft.
This is important on bigger machines in an industrial setting for proper transmission of motor torque to the load and also for efficient bearing operation.
If you have a small motor, measuring this is optional because your motor probably has a bearing wave washer anyway. Just make sure that the shaft is not badly bent.
But if you have a dial indicator, attach its base anywhere in the motor end bell where it will be stable and dial the shaft.
A deflection of more than 0.002 inches means that the shaft is bent and needs to be repaired.
3. Inspect your motor
Nothing is more surprising than finding out that your motor has a broken foot.
This is the time to check if your motor has missing bolts, dented fan cover, or any part that is broken.
Take note of each one because you can refer to them later during assembly.
This is also the best time to use your mobile device and start taking pictures.
Take pictures of the motor parts that you inspected.
Take pictures of the way the leads are connected in the terminal box
Take a shot of every step you do in disassembling the motor.
Picture of the nameplate. You might need the information in case the motor needs to be replaced or you found out that the motor needs rewinding. Remove any shaft attachment
4. Remove any shaft attachment
Helical gear attached to the end of the shaft
Some motors have a sheave or some kind of attachment on the shaft. Remove it first, especially if the bearings of the motor will be replaced.
Check the post, “How to remove a coupling, mounted gear, or pulley (sheave) from the shaft”
The basic tools you need to remove the attachment will be a bearing puller, a wrench, an Allen key if the attachment has a set screw, a snap ring remover if the gear is held by a snap ring, and a propane torch or oxy-acetylene torch in case it is tight.
Always measure the distance of the sheave from the end of the shaft so that you can put it back the same way.
If you have to use heat to remove the sheave, wear your safety glasses and protective gloves
Take pictures.
5. Remove the fan cover and the fan
Fan guard or cover of an electric motor
Not all electric motors have an external fan. Most totally enclosed motors have it and removing them can be straightforward.
Remove first the fan cover by undoing the bolts.
Cooling fans come in types and sizes. Check the post titled “Ways of removing the fan of an electric motor”.
The basic tool you need will be a pair of pry bars to remove the fan and depending on how the fan is held in the shaft, you might need a screwdriver, a snap ring remover, and a small socket wrench, or an Allen key.
6. Mark the end-bell (also called end shield, end cap, or end bracket) to the stator orientation
The Drive End (DE) of an electric motor refers to the end of the motor where the shaft drives the load.
The drive end shaft has load attachments which could be a sheave, a pulley, a gear, a coupling, or a blower fan.
The Non-Drive End (NDE) of an electric motor also called Opposite Drive End (ODE) refers to the end where the cooling fan of the motor is located. This is the end of the motor opposite the drive end
Most open drip motors don’t have a cooling fan or even a non-drive end shaft extension and so it’s closed but regardless, that end is called a non-drive end.
The end bell which is also called an end shield, end cap, or end bracket, is a part of the motor that covers both ends of a stator.
End bell also houses the bearings that support the rotor through the shaft called bearing housing. It helps to maintain the distance of the rotor to the stator core. This distance is called an air gap.
Reasons why electric motor stator and end bells are marked
The end bell to the stator must be marked because the stator core is not always in the middle of the stator housing which means if the rotor is installed backward, it will not be aligned with the stator resulting in the motor drawing a high current.
Putting the drive-end shaft to the non-drive end of the stator will also position the J-box (also called connection box, terminal box, or peckerhead) of the motor on the wrong side.
Installing the end bells upside down will put the grease nipples and sometimes the vent holes in the wrong spot.
The end bell and the stator are marked so that they can be assembled back the same way as it was. These are the ways the end bell and the stator are marked.
3 ways of marking the stator and end bell orientation
One punch mark on the non-drive end and two punch marks on the drive-end side
Two punch marks on the non-drive end and three punch marks on the drive-end side which we always do at the shop.
N letter punch mark on the non-drive end and D letter punch mark on the drive-end side
A paint marker is not advisable since it can come off anytime the parts are washed or cleaned with solvents.
Electric motors can have a double shaft like for example a shaker motor where both shaft extensions have the same diameter. In this case, it doesn’t matter which end is assigned as the drive end as long as they are marked.
7. Remove all the bolts fastening the end bells (end shield or end cap) to the stator.
The plastic cooling fan of an electric motor
There are different ways the end bells, also called end shields or end caps, are secured to the stator housing.
End bells directly bolted to the housing
Using through-bolts passing through inside the stator
Using through-bolts passing through outside the stator
Sometimes the bolts on one end are longer than the other. Take note of this so that you can put the proper bolt to where it is supposed to be.
Through bolts are also installed so that the nuts are on the drive-end side of the motor. Some manufacturers do this for a reason so put them back the same way.
Some bolts can be super rusty so it would help if you soak it first with an oil penetrant.
Use a parts bin so you won’t lose any parts. Be organized.
8. Removing bearing cap bolts from the end bells (end shield)
A bearing cap also called a bearing back cap, is a restraining plate installed at the back and sometimes at the back and in front of a bearing of an electric motor to ‘locate’ one end of the shaft while providing sufficient room in the other end for thermal expansion of the shaft.
The bearing cap ‘locates’ or held the bearing captive in the housing (usually the DE) to prevent axial displacement or movement of the coupling.
If there is a bearing cap you will not be able to remove the end bell from the shaft not until you remove the bearing cap first.
Two bolts on the end bell close to the shaft are an Indication that there is a bearing cap.
Sometimes both the DE and NDE end-bell have a bearing cap.
The bearing is locked in place on some motors using an internal snap ring right at the bearing housing.
The internal snap ring locking the bearing to the end bell can only be accessed once the rotor with the end bell still attached to it is removed from the stator
Some smaller motors have a bearing retaining ear instead of a back cap or snap ring to hold the bearing in place. Like the end-bell with the bearing held by a snap ring, it is easier to separate the endbell from the rotor if they are out of the stator.
9. If both end bells have back cap bolts, remove the non-drive end (NDE) back cap bolts first
There are advantages to removing the NDE bearing cap first although to some it doesn’t matter.
First is if you remove the NDE end-bell and the bearing housing fit is snug, the rotor will come with it which is annoying on bigger motors especially if you have to remove the rotor using a lift later.
Second, if the motor has an internal fan, it can be either on the drive end or the non-drive end of the shaft.
If the rotor comes with the endbell when you remove it, the internal fan will hit and can damage the windings of the motor.
10. Removing the NDE end bell also called end shield or the end cap.
End Bells are still held in two spots even after all the bolts are removed. One is on the stator rim and the other on the bearing. If the endbell clears these two, then it’s off the stator.
The usual way of removing it is by using a pry bar. On a very small motor, two flat screwdrivers are enough.
When prying the end bell, make sure to keep the tip of the pry bar from touching and damaging the windings.
8 ways to remove an end bell from the electric motor housing
Some motors have an opening notch between the end bell and the stator to accommodate the pry bar to pry an end bell off.
Some motors have cooling fins. Use the gaps between the stator and the end bell fins to pry and separate the two.
End bells have ears to accommodate the bolts. Tap this ear to rotate and be aligned with the feet of the motor or the fins of the stator and pry it from there
Another way is to use a dull chisel or a flat steel drift to tap and separate the end bell from the stator. Once an opening is made and the pry bar can fit, start prying the end bell out.
On smaller motors that don’t have a back cap, you can tap the shaft using a dead blow hammer in the direction of the end bell you want to remove. The dead blow hammer is made of polymer plastic and it will not damage the shaft.
Use a steel hammer and a piece of wood to protect the shaft if a dead blow hammer or any kind of mallet is not available
On smaller motors, if you remove the end bell and the rotor comes with it, that’s fine but make sure that there’s no internal fan on the other end. Or else you will be damaging the windings.
Some end bells are hard to remove especially when the bearing is seized inside the bearing housing. You can use a three-jaw puller for this job
Take your time.
11. Removing the DE end bell and the rotor of an electric motor
The rotor of an electric motor can be removed with the end bell still attached to it or without it.
The end-bell is removed first on bigger motors because a longer shaft extension is needed as leverage to remove the rotor out of the stator.
On smaller motors, if you remove the end bell and the rotor comes with it, that’s fine because there could be a snap ring holding the bearing inside the housing.
5 steps in removing the rotor and the end bell (end cap) of an electric motor with a bearing retaining snap ring
Removing the internal snap ring using a snap ring plier
Electric motors can have an internal snap ring inside the housing of the DE bearing instead of a back cap.
Bearings are held in place so that end play is minimized. Most roller motors have this as well as gearbox motors where the shaft cannot move back and forth.
Separate the end bell from the stator prying or tapping the other end of the shaft. See “5 Ways to remove an end bell from electric motor housing “
Once an opening is created, grab the top of the end bell with one hand and the shaft with the other and slowly remove the rotor out of the stator. Avoid hitting the windings.
Place the rotor upside down on a vise or similar stand.
Using a suitable size of internal snap ring plier, remove the snap ring.
Set the rotor on a piece of wood to protect the shaft and tap the end bell all the way around using a mallet until it separates from the rotor.
11 steps to remove the rotor and end bell of a capacitor start single phase motor
When removing the rotor and the end bell of single-phase motors, there are connection wires of the centrifugal switch that needs to be taken care of.
Some enclosed motors also have an internal fan opposite the centrifugal switch that you should mind.
Also, most centrifugal switches are on the non-drive end of the motor. Here is how you do it.
Remove all the through bolts and the fan if there are.
On a motor with a closed non-drive end (NDE) end bell, tap the drive end (DE) shaft with a mallet just enough for the NDE end bell to separate from the stator.
Using two pry bars or bigger flat screwdrivers, remove the end bell.
Using a needle nose or a long nose plier reach for the wire connectors and remove them from the switch.
Remove the NDE end bell.
Tap the shaft going the opposite way which is DE.
As soon as the end bell separates from the stator, grab the end bell with one hand and the shaft with the other and slowly remove the rotor.
On motors with an outside fan, most of the time you can just tap the NDE shaft using a drift or center punch until the fan, the rotor, and the DE end bell all separate from the stator.
Remove the rotor with the DE end bell still on it
In the process of removing the rotor, be careful not to bump the rotary switch to anything to avoid damage.
Then pry off the NDE end bell and remove the wiring connectors.
13 steps to remove the rotor and end bell (end cap) of a three-phase motor
Remove the fan covers and the fan of the motor.
Put punch marks on the end bells and the stator
Remove all the bolts securing the end bells
Remove the NDE end bell. See “5 Ways to remove an end bell from electric motor housing “
If the rotor comes out with the end bell, that’s fine, slowly pull the end bell until the rotor is halfway off the stator
Grab the rotor with one hand and the end-bell with the other and slowly remove it from the stator.
Pry the other end bell off.
If the NDE end bell comes off by itself, the next is to pry off the DE end bell. Again if the rotor comes with it, that’s fine. Slowly remove them from the stator.
Put the rotor with the end bell upside down on top of a block of wood and tap the end bell with a mallet until it separates.
Another way is while the rotor with the end bell is upside down on a block of wood, lift it then let it drop on the wood. The end bell should drop down.
On a larger motor with a heavier rotor, the end bell should come off when you pry it.
If the rotor is too heavy to manhandle, and your intention is just to replace the bearing, don’t remove the rotor. Remove and replace the bearing with the rotor on the stator then assemble it back together
If you have to remove the rotor, follow the steps in removing a heavier rotor out of the stator.
9 steps in removing a heavier rotor out of the stator
The rotor of a bigger motor, say between 25 HP to 100 HP motor might not be safe to remove from the stator even with two persons without a crane.
Some shops use a rotor lifting device to remove big rotors out of the stator.
If you have a chain hoist or a chain block handy, you can safely remove the rotor yourself. If the rotor is too heavy, you need them to support the weight of the rotor while removing it.
A hydraulic engine hoist or lift also will work.
Holding the DE shaft extension, pull the rotor out of the stator about a third out
With a sling rated at 3600 lbs. minimum, put a chokehold on the rotor
Using a chain hoist, lift the rotor until the weight is off the stator
Pull the rotor again until the haft of the rotor is out of the stator.
Let go of the chain hoist making sure the rotor is not touching the windings of the motor
Adjust the sling further to about a third the length of the rotor.
Lift the rotor again using the chain hoist until the weight is off the stator
While putting downward pressure on the shaft extension, slowly pull the rotor out of the stator. Keep the rotor from touching the windings.
If you need more leverage, insert a longer steel pipe on the shaft extension then put downward pressure on the pipe
Wear your safety shoes!
Conclusion:
Do you have a motor that you want to disassemble but are intimidated by the size or worry that you won’t be able to do it? You don’t have anything to lose so I would say go for it.
If you’re not successful you can always bring all the parts you disassembled to a shop and fix it for you.
It’s worth the try. Take lots of pictures. Work safe.
In a perfect world so to speak, an electric motor bearing can function for a very long time outlasting the motor itself.
The perfect condition for the bearing would be: that it is free of contamination, close if not perfectly aligned shaft, within tolerance shaft journal and housing fits, well-balanced and almost vibration-free rotor, ideal amount and good quality of lubrication, axial and/or radial load within the limit, and motor not experiencing overheating or overload.
But most of the time something always comes up and because the bearing is an integral part of the motor, once it fails other parts are most likely to be affected too.
When the bearing fails these are the things that can happen:
Shaft Journal wears out or damaged and needs to be plated and machined
Bearing housing wears out and has to be re-sleeved and machined
Rotor rubbing the stator laminations caused damage to the windings.
Collapsed bearing that makes the motor unrepairable.
If the motor is noisy and you are suspecting that the bearing is bad, It’s easy to say just replace it with a new one. Take apart the motor, remove the old bearing, slap in a new one, reassemble, and ‘done deal’. But not so fast.
The proper approach in replacing an electric motor bearing is to:
Disassemble the motor
Remove the old bearings
Inspect the windings, and the core for any damage
Check if the housing fits are good
Check if the bearing journal is good
Inspect the old bearings for any telltale sign of why the bearing failed and learn from it
Replace the bearing with a new one
Apply lubrication
Reassemble the motor.
If we have a better understanding of the motor bearing and what it can do if we neglect it, we can avoid costly mistakes.
1. Electric motor bearing failure can wear out or damage shaft journals.
Bearing Journal Right Beside the Centrifugal Switch
Bearing Journal is the part of the shaft where the bearing is in contact or located.
It has an interference fit which means the shaft journal diameter is bigger than the bearing bore or ID of the bearing inner race.
The shaft diameter is 0.0001 to 0.0004 inches (0.00254 to 0.01016 mm.) bigger than the inside diameter of the bearing. That is the reason why you need a puller to remove the bearing out of it.
The bearing inner race that sits in the shaft is stationary and is not meant to spin. They have standard tolerances, except for some special applications, to keep from spinning.
So why in the world will the journal wear out if the bearing is tightly held in place? It shouldn’t not unless the bearing inner race moves. But it will move and spin only if the inner race diameter of the bearing expands bigger than the shaft journal.
The metal expands with heat therefore if the bearing is hot due to for example lack of lubrication, the inner race will spin.
This metal-to-metal friction combined with the heat will wear the shaft journal not to mention the noise it will create.
Since the bearing is made of high carbon steel which is very hard, the shaft is more likely to wear out.
If the shaft journal is 0.0001 inches smaller than the minimum allowed diameter, it is considered worn out and needs to be repaired. That is unnoticeably small so how do we know if the shaft is undersized?
Besides obvious marks like discoloration on where the bearing sits on the shaft or bearing falling off the shaft without using a bearing puller, the best way to know if the journal is bad is by measuring.
Use a micrometer to see if the shaft is any good. If you don’t have a micrometer, bring it to a machine shop and have it measured for you.
The following table shows the minimum and the maximum allowed diameter of the shaft journal for every specific size of bearing.
For example, the size of the bearing you removed from the shaft is 6205. The table shows that the shaft diameter should be between 0.9844 to 0.9848 inches.
If you measure the shaft and it is 0.9842 inches or smaller, it has to be repaired. But if it is 0.9850 or bigger, that diameter is over the limit so the journal has to be polished down to 0.9848. If not, it will be too tight and it will just create damaging heat.
Table: Bearing Journal Tolerances
200 Series
300 Series
Maximum
Minimum
6200
6300
0.3939
0.3936
6201
6301
0.4726
0.4273
6202
6302
0.5908
0.5905
6203
6303
0.6695
0.6692
6204
6304
0.7879
0.7875
6205
6305
0.9848
0.9844
6206
6306
1.1816
1.1812
6207
6307
1.3785
1.3781
6208
6308
1.5753
1.5749
6209
6309
1.7722
1.7718
6210
6310
1.9690
1.9686
6211
6311
2.1660
2.1655
6212
6312
2.3628
2.3623
6213
6313
2.5597
2.5592
6214
6314
2.7565
2.7560
6215
6315
2.9534
2.9529
6216
6316
3.1502
3.1597
6217
6317
3.3472
3.3466
6218
6318
3.5440
3.5434
Shaft Journal Fit Tolerances – NEMA Standard
How to repair a shaft journal.
A worn-out or damaged electric motor shaft journal is repaired by Nickel or Chrome plating through an electrolysis process.
The rotor is mounted on a rotating machine but before going into the process, the shaft journal undergoes degreasing and then sandblasting using glass bead or silica sand while rotating to ensure proper adherence of the plating metal to the shaft.
Bearing Journal Repair by Plating
The machine where the rotor is mounted will serve as the negatively charged electrode and the wand with continuously flowing metal plating solution is the positively charged electrode.
This special wand allows the even distribution and build-up of metal to the specific part of the shaft while the rotor is slowly rotating.
All other parts of the rotor are taped or masked to avoid coating deposits on all other surfaces.
The diameter of the bearing fit is repeatedly checked until the build-up of metal is within the tolerance then it is lightly polished.
The length of time for the process is about 30 minutes to even hours depending on how thick the required build-up will be.
Other ways of fixing a worn-out shaft journal are:
Electroless nickel plating uses a chemical autocatalytic reaction to deposit the coating instead of electrolysis
Machining the shaft journal and building it up again by welding. Then it is machined back to the proper size. This allows a solid metal to metal bonding
The use of spray welding instead of the regular welding to build up the shaft journal before machining it back to the right size
Machining the shaft down and inserting a pre-machined sleeve. EZE Sleeve or EM Quik Sleeve are examples of the ready-made sleeve.
Of course, all of these repairs don’t come cheap. Buying a new one might be an option not unless the motor is special and pricy like a double shaft motor or threaded shaft.
A patch-up job offers a temporary fix to a worn-out shaft journal. It is not recommended but it can be used during emergencies until the replacement motor becomes available;
One way is to apply a dab of Loctite retaining compound before bearing installation. Just a small dab will do the work. Putting too much can contaminate the rolling elements of the bearing.
The downside of Loctite is that when the bearing overheats again, combined with vibration, this adhesive breaks down and the motor is back to the same situation.
Another way is by putting chisel marks or punch marks around the journal. Then the bearing is installed using a bearing driver.
Of course, again, these are just temporary fixes.
2. Electric motor bearing failure can cause housing to wear out or damaged
Bearing housing is a part of the electric motor end shield that houses the bearing. It has a sliding fit or also called clearance fit which means the housing diameter is slightly bigger than the bearing outer race or OD of the bearing.
Damaged Bearing Housing Visible Discoloration
For example, the housing diameter of a 6208 bearing is 0.0001 to 0.0008 inches (0.00254 to 0.02032 mm.) bigger than the outside diameter of the bearing to allow for bearing expansion.
That is the reason why you can remove the end shield from the motor by just prying it out or installing it by just sliding it in. Not unless there is a snap retaining ring holding the bearing in place inside the housing or the bearing is full of rust.
The bearing outer race that sits in the housing is stationary and is not meant to spin. They have standard tolerances to keep them from spinning as soon as they expand during operation.
Retaining compounds such as Loctite is not necessary for as long as the housing is within tolerance.
Excessive axial and radial load combined with the rise in temperature due to lack of lubrication wears out the bearing housing.
When the bearing housing wears out, the diameter increases allowing the bearing outer race to spin in the housing
This metal-to-metal friction combined with the heat will not only wear out and damage the housing but will also create a squealing noise.
Since the bearing is made of high carbon steel, the housing is more likely to wear out.
If the bearing housing is 0.0001 inches bigger than the maximum allowed diameter, it is considered worn out and needs to be repaired. That is so small, how then can we know if the bearing housing is bad?
Obvious marks of discoloration on where the bearing sits on the housing would tell that the housing is bad. If there is no mark of wear, the housing should still be checked.
One way is by using a test bearing. It can be a brand new or a slightly used bearing, the same size as the one you removed.
This is how to check the bearing housing using a test bearing.
1. Clean the bearing housing. Remove any grease and dust particles.
2. Remove rust if there’s any by using a scotch pad or fine-grit sandpaper. After cleaning, lightly smear it with any kind of machine oil
3. Clean the test bearing. It should be the same if not the actual bearing removed from the shaft. Don’t worry about the bearing being worn out because they are made of high-carbon steel. Dab it with a thin layer of oil.
4. Install the bearing to the housing. If you do it straight and not on an angle, you should be able to do it by hand. Use a rubber mallet and tap it all the way around if you need to
5. Using your index finger and thumb, try to wobble the bearing side to side. A good bearing does not show any visible movement between the housing and the bearing outer race. Do that in different locations around the bearing.
6. Again using your index finger and thumb, try to rotate the bearing. You shouldn’t be able to spin or even move the bearing inner race on a good housing. If it does, the bearing housing is worn out.
The more accurate way of knowing if the housing is good or bad is by measuring.
Use an inside micrometer to see if the housing fit. Again, if you don’t have a micrometer, I suggest you bring it to a machine shop and have it measured for you.
The following table shows the minimum and the maximum diameter of the bearing housing for every specific size of bearing.
For example, the size of the bearing you removed from the shaft is 6208. The table shows that the housing diameter should be between 3.1503 to 3.1496 inches.
If you measure the housing and it is 3.1497 inches or bigger, it has to be repaired according to the tolerances given on the table. But if the housing diameter is 3.1502 or smaller, that diameter is undersized so the housing has to be polished up to 3.1503.
Housing that is too tight for the bearing will only create damaging heat due to a lack of room for bearing outer race expansion.
Table: Bearing Journal Tolerances
200 Series
300 Series
Maximum
Minimum
6200
1.1816
1.1811
6201
1.2604
1.2598
6202
6300
1.3756
1.3750
6301
1.4573
1.4567
6203
1.5754
1.5748
6302
1.6541
1.6535
6204
6303
1.8510
1.8504
6205
6304
2.0479
2.0472
6206
6305
2.4416
2.4409
6207
6306
2.8353
2.8345
6208
6307
3.1503
3.1496
6209
3.3474
3.3465
6210
6308
3.5443
3.5433
6211
6309
3.9379
3.9370
6212
6310
4.3316
4.3307
6213
6311
4.7253
4.7244
6214
4.9223
4.9213
6215
6312
5.1191
5.1181
6216
6313
5.5128
5.5118
6217
6314
5.9065
5.9055
6218
6315
6.3002
6.2992
6219
6316
6.6939
6.6929
6220
6317
7.0876
7.0866
Bearing Housing Fit Tolerances – NEMA Standard
How bearing housings are repaired
Bearing housings are repaired by machining. This is done by installing a sleeve and then machining it down to the proper size. For example, you have an end shield that has a bearing size of 6209.
This bearing has an actual outside diameter of 3.3465 inches (85 mm.) and a depth of 0.748 inches (19 mm,)
Procedure:
1. From a steel pipe material, machine a sleeve with an outside diameter of 3.597 inches, an inside diameter of 3.297 inches, and a depth of 0.945 inches.
Chamfer cut one of the outside diameter edges.
2. Put the end shield also called the end bell on the four jaw lathe machine chuck and dial the machined outer edge.
3. Make sure that the face and the rim surface of the machined end bell edge are dialed to or close to zero.
4. Or, instead of the face of the end bell edge, you can dial the machined portion of the bearing housing which is parallel to the lathe machine chuck.
5. Machine the worn-out bearing housing down to 3.592 inches. Do not put any chamfer on this part.
6. With the chamfered side going in first, install the pre-machined sleeve into the bearing housing.
Tap it in using a steel or aluminum hammer. Do not worry about denting the edges of the sleeve. It will be machined afterward.
7. Dial the rim and the face of the end bell again to zero making sure it didn’t move during sleeve installation.
8. When the sleeve is fully inside the bearing housing, there will be an extra length of sleeve material sticking out. Use this portion to make a trial cut before proceeding with machining the sleeve.
9. Machine the bearing housing according to the tolerances given on the table for a 6209 bearing.
10. Machine off the extended portion of the sleeve and put a small chamfer to facilitate bearing installation. Done!
The machined housing’s diameter is 3.592 (91.2368 mm) while the sleeve is 3.597 (91.3638 mm). The sleeve is 5 thou (0.127 mm) bigger than the machined housing.
That clearance is important because if the fit is too big, the sleeve can warp but if it is too small, it can spin in the housing.
There are also other ways of installing the sleeve to the machined housing like freezing it using nitrogen and also by pressing it using either an arbor or hydraulic press, or the tailstock of the lathe.
Instead of machining a sleeve, ready-made ones are commercially available for example EZE- Sleeve or EM-Quik-Sleeve which are available in the market.
Although that in my opinion is the best way to fix worn-out bearing housing, there are other ways also. Some of them are:
a) Electroplating uses a nickel plating solution to deposit the metal coating through electrolysis.
b) Machining the bearing housing and building it up again by spray welding.
After the proper amount of metal build-up, it is machined back to the required size as indicated in the table.
c) Machining the bearing housing down and inserting a wavy tolerance ring.
d) Buying a replacement end bell for the particular brand and model of your motor.
Again, repairing a cheap motor may not be worth the time and money since electric motors nowadays are cheap, not unless the motor is special, pricy, or hard to find.
Temporary fix of the worn-out bearing housing.
I call it a patch-up job. It is not recommended but it can be used during emergencies until the replacement motor becomes available
1. One way is to apply a dab of Loctite retaining compound before bearing installation.
I recommend this only if the bearing housing is over by about 0.0001 to 0.0002 inches from the maximum tolerance given in the table.
Just a small dab will do the work. Again, putting too much can contaminate the rolling elements of the bearing.
Once again, the downside of using Loctite is that when the bearing overheats, combined with vibration, this adhesive breaks down and the motor is back to the same situation.
2. If the bearing housing is damaged already, you can patch it up by putting punch marks using a center punch around the housing.
The punch marks will create raised dents all around the bearing housing that will fit with the bearing a bit tighter.
A Loctite retaining compound can also be added to fill up the gaps.
3. Another way is by putting a knurl on the bearing housing. This is done by using a handheld knurling tool.
This will create crossed patterns with raised areas around the bearing housing that will make the bearing fit snug. Sometimes used in combination with Loctite retaining compounds.
Of course, again, these are just temporary fixes.
3. Bearing failure can cause the rotor to rub the stator causing damages
The bearings allow the rotor to spin inside the stator. Without the bearing that is not possible.
The magnetic flux on the stator will try to grab the rotor but because the bearing supports the rotor on both ends it will instead create a rotational magnetic flux to keep it spinning.
The gap is about 0.016 inches (1.5 mm). Maintaining that small air gap between the spinning rotor and the stator is important not only for the efficiency of the motor but also to keep them from rubbing with each other.
If the bearing and the housing get damaged, the gap closes in and the rotor will touch and rub the stator.
Damages caused by the rotor rubbing the stator:
a) Stator lamination fuses together creating damaging heat
b) The laminated steel of the stator dragged sideways can result in shorted motor windings.
c) Rotor causes damage to the top wedges exposing and shorting the wires causing blow-up.
d) Bad rotor damage might require laminations to be restacked
Stator lamination fuses together creating damaging heat
The stator of an electric motor is made up of layers of 0.020 inches (0.5 mm) thick silicon steel laminations, individually coated, then stacked together to form the core of the stator.
The coating between layers of the silicon steel creates an inter-laminate resistance that helps in minimizing hysteresis loss and eddy current or circulating current in the core.
These losses have to be kept to a minimum so that the core will not heat up.
Fused Stator Laminations When the Rotor Rubs the Core
When the rotor rubs the stator, these laminations are fused together creating what we call “hotspots “.
When the motor is running, heat is produced in that portion of the stator and it is enough to burn the insulation causing the wires to be shorted to the core-
The laminated steel of the stator dragged sideways can result In shorted Motor windings
The stator core of an electric motor is not one solid piece of metal. They are thin layers of laminated steel tens to hundreds of them stacked together to form the core.
The portion of the lamination closest to the rotor is called a stator tooth and the space between teeth is called a stator slot.
Coils or magnet wires are in these stator slots and they are prevented from touching the steel core using insulation paper.
When the rotor rubs the stator, the tooth gets dragged sideways pressing onto the insulation and the coil creating electrical shorts.
I see this happen on smaller motors where the tooth width is narrow. The thin edges of the laminations tend to damage the insulating papers protecting the coils.
Rotor causes damage to the top wedges exposing and shorting the wires causing blow-up.
Top wedges also called top sticks are inorganic high-temperature insulating materials like NOMEX by DuPont or CeQUIN by 3M.
They are insulating papers formed into wedges and inserted right on top of the coil to protect and keep it from coming out of the slot.
Most of the time they are situated close to the surface of the stator and when the rotor rubs into it, they get damaged and stripped. The exposed wires are then rubbed to the spinning rotor blowing up the shorted wires.
Bad rotor damage might require laminations to be restacked
A stator core is made up of tens to hundreds of thin laminated silicone steels stacked together to form the stator core.
These laminated steel called laminations are magnetically insulated from each other.
It is designed this way to minimize eddy current or circulating current in the stator core because of the lower core power factor, and watts per pound of the stator.
When the rotor rubs the stator badly, there will be a need to re-stack the core especially if the motor is irreplaceable, the motor is special, or the new motor delivery will take a while.
If besides the stator the rotor is also damaged, the motor will be scrapped. The motor is beyond economical repair
4. Motor with collapsed bearing makes it unrepairable
Neglect and inexistent motor maintenance result in bearing collapse. This happens when a portion or all of the bearing balls comes off from inside the bearing.
The extent of damage makes the motor unrepairable or at least economically. It could be a combination of damaged end shield bore, two bearing housings, one or two journals, damaged rotor bars, stator core needing re-stacking, and/or rewind. It can be very expensive.
Tips on how to avoid bearing failure:
1. Regularly check the motor performance.
A maintenance checklist indicating the motor identification, temperature, noise level, vibration, date, and remark will be best for this, especially in an industrial setting.
Any abrupt change is a telltale sign that the motor needs attention.
.
2. Regularly have the bearings replaced. Bearings are cheap compared to the cost of replacing or repairing a motor.
Once a year or every two years, have it overhauled and the bearings replaced especially if the motor is loaded to its max.
3. Avoid subjecting the motor to water or corrosive chemicals to avoid rusting. There is at least 0.001 inches gap between the shaft and the end shield bore so water and moisture can go in.
When the motor is warm from the operation and then it will be idle for some time, rust develops in the bearings.
4. Replace or lubricate the bearing at the sign of an increased level of noise.
A small magnetic humming and noise coming from the fan windage are normally expected on a motor. But more than that, the bearing has to be lubricated
Lubricating a motor that doesn’t have a grease nipple might be a challenge. So, having the bearings replaced is a good option.
Conclusion:
Most electric motor damages can be prevented just by keeping their bearings in good shape
As I said, brand new bearings are cheap compared to the motor, and don’t even consider repacking it. Not worth it.
When the bearing makes noise, the damage to its outer race is done.
