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For the preservation and enjoyment of 1928 to 1931 Indian Scout Motocycles
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Bosch ZEV Magneto Cutout

  • 13 Jun 2017 3:33 PM
    Message # 4898685

    Hi,

    The Bosch ZEV magneto fitted to my 1928 101 needs overhauling, and i'm looking at what parts I can get.

    I need a new cam ring as mine has been modified - I see these are available on ebay.

    Also from the same seller is a cutout connection for grounding the magneto - would a cutout have ever been fitted to a 101?

    Or has anyone else added one? Seems like a good idea to me.

    Any comments welcome before I part with my hard earned cash!!

    Cheers Mick


  • 17 Jun 2017 10:25 PM
    Reply # 4905716 on 4898685

    Cutouts or killer switch are needed on Fours that doesn't have a valve lifter as the other engines, and some, if not all sport handlebars has 2 signal horn buttons, one for a killer. Killers are neat if you want to speedshift, just cut the mag for a moment and push the shifter to next gear quickly. Common practice on dirttrack bikes. But for heaven's sake, don't do that on downshift...A killer switch can be convenient, but I haven't found it necessary.

    I am no expert on ZEV's but if your breaker cam is modified, it might be a sign that the rotor is not really suited for the 42 deg. cylinder split on an Indian. What I understand is that the rotors in ZEV's are adapted with cut-out portions for different V-twin angular split, all from 15, 30, 42, 50, 80 and 90 degree angular splits and more. If there is a big different in spark strength if you should use a 30, 45 or 50 degree rotor, that I don't know, there is others that can answer that better than me. The D-type mag/gen rotor is not adapted in the same way as the ZEV rotor.

    Last modified: 17 Jun 2017 10:52 PM | Carl-Erik Renquist
  • 19 Jun 2017 2:28 PM
    Reply # 4907782 on 4898685

    When i got my 28, it had sport bars with the ground switch attached.  When i replaced the bars, i also deleted the switch since like Carl says, it's redundant with the compression release on the case.

  • 20 Jun 2017 6:36 PM
    Reply # 4909986 on 4898685

    Hi Carl-Erik.

    Thanks I appreciate your advice. I take your point about the decompressor which I must say had slipped my mind.

    I guess when the magneto is reconditioned - They will find out if the armature/rotor is correct.

    So at least the new cam ring I have ordered will be correct!

    Regards Mick

  • 21 Jun 2017 1:11 AM
    Reply # 4910310 on 4898685

    Yes, but you can ask the right questions. Is the rotor really a 42 deg? is the coil rewound and what method and what sealer used for sealing it? Is after sealing, then the rotor balance checked and adjusted? 

    You can ask the particular numbers of the 2 coils resistance and isolation value, ask about the safetygap gap and what manufacturer and type of condenser used. 

    And what magnetizer gear used, it has to be strong enough. Most good ones are large and heavy. Two things go into design of an electromagnet. The number of amp-turns (AT) and the magnetic permeability of the pole pieces. I don't go into the permeability here. 6000 Ampere turns or better is about what is required to saturate an ordinary magneto magnet. 

    What test method used to check the finished result? Is it durance tested in a hot state? What spread in ignition timing does it have when running, it should be within a couple of degrees at the max. And you can ask what particular things you should check in the future, to know wear limits and things good to know when a service or refurbish is needed. 

    If they can answer all that with numbers and confidence, then I would trust them, at least a bit further than I can throw a stone...But I still would check it over, all screws and nuts. And the shaft in-and-out play. It should be zero or very close to zero. 

    Last modified: 21 Jun 2017 1:50 AM | Carl-Erik Renquist
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