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re: rebuilding electric motors?

To: Mike Lee - Team Banana Racing
Subject: re: rebuilding electric motors?
From: Scott Beckman <>
Date: Wed, 4 Dec 1996 07:29:56 -0800
>  From: Mike Lee - Team Banana Racing <>, on 12/3/96 
>  9:35 PM:
>  Is anyone here familiar with rebuilding electric motors?  I didn't
>  feel like shelling out $150 to replace the starter in my car with
>  a rebuilt one (it's a Mitsubishi MIT74281ZC, btw), so I took it
>  apart to see what was wrong.
>  Well, it looked like the brushes were worn out, and surprisingly,
>  the Jeep dealer could order a new set for $35.  2 of the 4 brushes
>  were soldered onto the brush holder assembly, so I had to get them
>  that way; I supposed I could have gotten them more cheaply somewhere
>  else, but I don't think my Weller would be up to soldering those wires!

You might have been able to get them from another supplier, but $35 is a good
price from a dealer.  Plus you know they are SUPPOSED to fit.  

>  My question is about the armature; I cleaned out the grooves between
>  the copper contact strips with a pick (I figure the buildup in there
>  might have been causing some shorting).  The copper strips also seem
>  kinda pitted.  Is there something I should do to it?  Perhaps a little
>  light sanding with #400 to clean it up?  Also is there any sort of
>  lube that should go on the brushes; the original ones seem to have some
>  sort of greasy residue on them.

I don't see a problem with lightly sanding the contacts.  Just don't go too
deep, there may be some kind of coating on there.  But it may just be some kind
of copper mix. Either way, be careful. 

You can clean the armature with just about anything, even soap and water will
work.  Just be sure to dry it COMPLETELY before you assemble it.  BTW, in the
NAVY, we used to use LOW pressure air to clean windings.  I don't think it is
the best way to clean motors, but it works.  You may want to check the
insulation resistance between the contacts and the insulation.  The higher the
resistance the better, should be higher than an 1 meg ohm.  Also check the
resistance between the contacts, it should be less than an ohm.   

I believe the brushes are made out of carbon.  If that is the case, there is
no need for any lube!

BTW, you may want to clean the stator while you are at it.  If you don't know
what that is, it is the windings around the armature.  Clean it and check it
the same way as the armature.  

>  TIA,
>  Mike

Good luck!
Scott Beckman

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