Armature problem

tictac

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I have several Black & Decker corded mowers, all 120V, 12A, 18". I had to replace brushes on one, so I decided to remove the magnet shell in order to give the motor a good cleaning. After re-assembly the armature would not spin freely. I double checked ALL places where it could bind or rub on something and found absolutely nothing. It appeared to be some magnetism between the PM and armature. I decided to take another B & D (that worked well) and remove its magnet, just to compare things. The same thing happened on this one. I re-assembled it VERY, VERY CAREFULLY. Nothing was rubbing, only a magnetic force that prevented it from spinning really freely. When these two mowers were re-assembled, the brushes just sparked because they could not overcome the drag on the armature. Does anyone have any thoughts on this? Thanks in advance.
 

Rivets

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A few things come to mind. First, are you positive that you have not forgotten shim washers on both ends of the armatures? Second, did you make sure that the case was put back the same way it was removed? Third, will it spin freely without the brushes installed? Reason I ask these questions is, shim washers help with the alignment of the armature. In some instances a case is turned 90 degrees when reassembled and not allow a perfectly straight line between the bushings. If you cannot turn the armature freely with no brushes you have an alignment problem or you are over tightening the screws. To anyone else who may want to disassemble an electric motor or starter motor, never start disaasembly without first marking all case parts first for accurate reassembly later.
 

tictac

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Thank you for the advice. I did not have the armatures out of the bottom end caps, but when the magnet assembly was pulled off the top of the armature it had quite a magnetic force and possibly dislodged a shim at the bottom end cap. Thanks for bringing that to my attention. Even with no top end cap, and therefore no brushes, the armature was still too stiff to turn freely. I will pull the armatures off the bottom end cap in the next day or so and report back.
 

Rivets

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The armature will not turn freely without both end caps in place. They are your alignment points, as they will keep it in a straight line. Many times you will have to screw everything together to properly space the armature between the magnets.
 

tictac

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The armature will not turn freely without both end caps in place. They are your alignment points, as they will keep it in a straight line. Many times you will have to screw everything together to properly space the armature between the magnets.

I played around with both motors some more and found the following:
- The armature is mounted vertically and pressed into the lower end cap which has a bearing. This gives the armature just about zero end play and very little side-to-side wiggling. So with only these two parts assembled (no upper end cap; no brushes; no permanent magnet) the armature spins easily with a twirl of two fingers and keeps on spinning.
- When adding the permanent magnet housing (still no top end cap) the armature still spins freely but with a slight rubbing on the magnets. This is what I have on one motor now. On the other motor, the adding of the magnet housing appears to give the armature much more drag. So I continued assembling the better motor.
- Adding the top end cap has no effect on end play; it just provides a bushing to keep the armature away from the magnets. It still spins fairly well now.
- Adding the brushes created a bit more drag, but I think it may start now. I need to repair the switch on the handle before I can try it. I will report after doing that.
 

tictac

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The one motor is working properly now, although I didn't determine what made it spin more freely the last time I put the magnets on it. The only thing left is to take the bad motor armature and re-assemble it to try and get it to spin more freely. Then I may have two working mowers. Thanks for your suggestions so far.
 
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