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Checking Bosch DVAR Carbon Brushes on a 101

  • 12 Jul 2023 11:24 AM
    Quote
    Message # 13226863
    Robert Lodge

    (1) I may be just complaining out loud here but maybe I'm also missing something.

    When my '28 101 would no longer start I did what I have never bothered to do before -  check the magneto brushes!  Indeed, one was completely worn away so I replaced both with new. Easy to do on a Splitdorf NS2.

    Now my '31 101 (from Europe - I'm in U.S.) with a Bosch DVAR is having ignition missing and getting hard to start so naturally I wanted to check the magneto brushes. If they are anything like the ones in a ZEV they would be rather short (5mm diam, 8.75mm long beyond spring) and must have short lifespans.

    I found the front DVAR pickup impossible to remove as the screw is directly behind the 101's front left tube and the rear one is close to impossible to reach even with my bendable screwdriver. So I will have to remove the magneto just to check the brushes - something I was not planning on doing until winter cold. Its good I am waiting for delivery from Europe any day now of a DVAR I just had rebuilt.

    (2) Its been many years since I replaced a magneto. Can someone suggest the best flywheel and cam position to impose the maximum rotational pressure on the timing gears to help hold them from falling out when removing the cover?

    Thanks,

    Bob
  • 14 Jul 2023 5:12 AM
    Quote
    Reply # 13227723 on 13226863
    Carl-Erik Renquist

    Brushes needs to have the right hardness in order not wear too fast or score the contact rings. In the DVA magneto there is 3 brushes, one behind the points block. You could have a fourth one in the bakelite lid cover if the mag was equipped with that, for the killswitch. Hardness comparement should always be done with new bought replacements or homemade ones as well. Manufactures have numbers of the hardness but a rough comparement could be checked by scribing a line with the brush on a hard white paper and compare the colour and width of the line with the replacement. In doubt, rather use softer than harder brushes. It is always easier to replace the brushes than replace the contact rings. Retaining springs is important as well, local overheating can make the thin wire gauge springs soft. It is hard to mention some numbers, I have most measurements but not brush sizes or spring ratings. Pictures from the article:

    Restoring a Rotating Armature Magneto [Re: Magnetoman]

    John Healy Online content

    BritBike Forum member

    Years ago BMZ Bayerische Magnetzünder GbR had all replacements for the DVR but I don't know now.

    And a picture of the regulator function from another article.

    5 files
    Last modified: 14 Jul 2023 5:49 AM | Carl-Erik Renquist
  • 15 Jul 2023 4:19 AM
    Quote
    Reply # 13228200 on 13226863
    Ken Lee

    Hope this may help and hope you can open it . Ken


    1 file
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