Starter motor - arcing marks on end cover and brush holder

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  1. #1
    CelicaSupra.com Member Suprabee's Avatar
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    Starter motor - arcing marks on end cover and brush holder

    So, was taking apart my MKIII spare starter to rebuild it, clean it ect...

    I noticed these arcing marks between the end cover and brush holder.

    Everything on the field frame, brushes, meters out correctly with continuity and no continuity where applicable.

    I can't seem to understand why these arcing marks are present. The negative side brushes have continuity to this back plate which is then bolted to the end cover which is grounded to chassis.


    any thoughts on what caused this, and more importantly is this a reason not to rebuild it?

    thanks
    rick



    86 P-type, 5-spd, SDR, Gray Leather, 161k
    92 MKIII Black, Auto, Shadow Gray Leather, 232K- daily driver

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  3. #2
    CelicaSupra.com Member Suprabee's Avatar
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    ok.. after some closer inspection and thought, I'll take a stab at answering my own question.


    In a "clean and new" situation, the negative brushes have a path to ground through the back plate, then through the screws that hold the end cover on to the back plate. Over time, buildup of dust/moisture, etc.. caused resistance to originate between the two screws and the back cover, as well as, the physical contact point of the back plate and end cover (where the arc marks are). Eventually this resistance build up enough that arcing occurred directly from the back plate to the end cover.

    Although my camera will not take a close up of the two screws, I can see (with my magnifying hood) that some of the threads on the screws show signs of arcing as well.

    That's my best theory, and as long as I clean up these contact areas of the plate and cover and perhaps use 2 new screws then a proper path to ground will be established, and no arcing will occur. (at least until buildup of dust/corrosion occurs again)


    rick
    Last edited by Suprabee; 09-14-2019 at 06:25 PM.

  4. #3
    CelicaSupra.com Member RedP85's Avatar
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    Rick, a bit like spot welding: high current in a small surface. The crank Amps is nowhere near spot welding, but still high. Enough to, in the long run, do local pitting on the surfaces.
    -Jocelyn,
    P85-6MGE SDR(HKS kit c/w IC and F-Con in a box) 225KKm, NAL seats, 2.5 Brullen, ACT clutch, LJM, SS lines, Trip Computer. EuroH4
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  6. #4
    CelicaSupra.com Member Suprabee's Avatar
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    yeah, makes sense.

    I ground off the pitted areas with my dremel on both the plate and the cover, however there was so much material that was pitting and then removed when I put the dremel to it, that there was a gap between the cover and back plate at those areas. I took two .5 mm thick small washers and used them between the plate and cover to fill up the gap. Cleaned up the screws and threads in the cover and plate, and it now fits together snug.

    I'm now just waiting for a new plunder and plunger contacts for the solenoid and then give it a test crank (off the car of course).
    86 P-type, 5-spd, SDR, Gray Leather, 161k
    92 MKIII Black, Auto, Shadow Gray Leather, 232K- daily driver

  7. #5
    CelicaSupra.com Member drjim's Avatar
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    I'd use a dab of either aluminum or copper antiseize compound between those new parts. The metal in the compound improves conductivity, and grease seals out moisture.
    1985 5-speed "Ms. Swan"

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  8. #6
    CelicaSupra.com Member Suprabee's Avatar
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    Quote Originally Posted by drjim View Post
    I'd use a dab of either aluminum or copper antiseize compound between those new parts. The metal in the compound improves conductivity, and grease seals out moisture.
    Ah yes, good idea, I have some copper anti-seize that I used on an old Subaru's OX sensor.

    will do,
    thanks
    rick

  9. #7
    CelicaSupra.com Member drjim's Avatar
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    I like "Jet Lube SS30", it's copper-based, and thick enough that it stays put. I use it on antennas, but it works great as a general purpose antiseize, too.
    1985 5-speed "Ms. Swan"

    OH, What A Feeling!

  10. #8
    CelicaSupra.com Member AJ's Avatar
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    IF Doc uses it I'm ALL IN!!

    Quote Originally Posted by drjim View Post
    I like "Jet Lube SS30", it's copper-based, and thick enough that it stays put. I use it on antennas, but it works great as a general purpose antiseize, too.
    Regards,
    Arch
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