electric motor rotor frozen to stator (rust?), how to loosen?

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  #1  
Old 03-05-18, 02:18 AM
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electric motor rotor frozen to stator (rust?), how to loosen?

I have a 12v electric pump that's sat in storage for 25 years. When I pulled it out yesterday and tried to test it, the shaft wouldn't turn. Disassembling it showed a fine layer of rust on the rotor and stator and that they are stuck together.

I don't want to break anything, and don't want to randomly pour some rust busting liquid over rusty area hoping it will soak in and loosen things up. Can someone advise me on the correct way to take care of this problem?

John
 
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Old 03-05-18, 04:43 AM
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No special secret. Somehow you have to get the parts separated. Wiggling and light tapping would be my first step. Them possibly putting the motor in a press to apply more force. Do NOT use heat as you could cause a magnet to come unglued or damage with windings. How are the bearings?
 
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Old 03-05-18, 06:08 AM
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I'd start with some wiggling and light tapping too, but if I don't see anything happening with that my next step is usually to put some steady pressure on it for a day or two and see if that helps. It's gotten to where it is over a number of years, so reversing it often isn't a 5 minute fix. Sometimes a puller along with a little creativity works, sometimes there is a solid enough boss to back the head of a bolt against, or maybe even a wedge of some sort.
 
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Old 03-05-18, 07:41 PM
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I took the metal cover all the way off(a strong and mysterious force was holding it in place before, turns out to be magnetism) and after that the two magnet pieces that were stuck to the rotor were easy to remove. I've included a photo link below so you can see what I have. I've only taken apart generators before this so I'm not sure what to make of this setup. There is no stator coil on the inside of the outer cover, just these two curved magnets that seem to be free floating and conform to the rotor's curvature.

So how best to clean up the rust? Should I use a metal brush, sandpaper, a plastic scrubber, a scrapper of some kind. And can I test the rotor coils with a DVOM, and how would I do that?

Also, for reassembly...these two curved magnets don't seem to have a fixed place where they attach, should I just put them anywhere they fit around the rotor? I'm at a loss because I've never dealt with this kind of motor before.

Here's the photo, I have more closeups if necessary

 

Last edited by jbclem; 03-05-18 at 07:47 PM. Reason: https://www.dropbox.com/s/qmiwujuvw7a2m20/P1220354.JPG?dl=0
  #5  
Old 03-05-18, 07:46 PM
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The photo link didn't stick to the previous message...here it is again.

https://www.dropbox.com/s/qmiwujuvw7...20354.JPG?dl=0

Name:  motor_L.jpg
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Last edited by PJmax; 03-05-18 at 08:32 PM. Reason: modified/added pic from link
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Old 03-05-18, 08:35 PM
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Had a hard time getting the modified dropbox picture to post. They put something in it to keep ownership with poster. The dropbox link is still active.

Anyway.... those two half round pieces of ferrite are the magnets that should be glued to the motor cover. They do have a specific location to be in. Look for the old glue marks.

I usually clean rust with Kroil. It's a rust remover. You need to check the brushes and bearings for condition too.
 
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Old 03-06-18, 05:05 AM
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That's a basic DC, brushed motor. They don't get much simpler. As PJ mentioned you need to glue the magnets back into the correct locations so you don't mess up the timing, but it should be pretty forgiving.

The bearings may be pitted from rust but a good cleaning and oiling/greasing should get them working at least for a while. If this motor is only going to be used occasionally I'd just go with cleaning up the old bearings but if this is something that will get a lot of use I would measure the bearings and get new ones on order since the motor is already apart.
 
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Old 03-07-18, 12:42 AM
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Inside the outer cover I can see some outlines that will help in locating the magnets...but when I clean up the inside, which is rusty also, the outlines may vanish so I'll have to try to mark them first. Do you suppose scribing some lines in the metal would create a problem?

For cleaning off the rust, I have PB Blaster penetrant and rust remover, but it leaves a film. So would something like 3 in 1 oil. Since we're dealing with magnetism, maybe a film wouldn't matter although it could spin off and cause a problem. And to glue the magnets back in place I'll need to keep the glue area clean and dry. I'll probably start with a metal bristle brush or even a toothbrush and see what happens.

Any suggestion for a metal to metal glue?
 
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Old 03-07-18, 05:16 AM
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Scribing would work or you can make marks on the outside of the case.

I would lightly sand to remove the rust. That way you don't have any concern about a residue left behind that would prevent glue from sticking. Here is a .pdf that will tell you more about gluing magnets into motors than you ever wanted to know. You haven't told us what the motor is used for so it's hard to recommend if a "regular" type glue will be adequate.
 
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Old 03-12-18, 02:44 AM
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Pilot Dane, I don't see the link for the pdf you referred to...I'd like to read more about gluing the magnets back in place. This motor is from a 12v Jabsco electric Marine Toilet, it's called a macerator pump.
 

Last edited by jbclem; 03-12-18 at 03:48 AM.
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