The 101 Association, Inc.
For the preservation and enjoyment of 1928 to 1931 Indian Scout Motocycles
"You can't wear out an Indian Scout"

Splitdorf magneto 101 '29

  • 09 Nov 2018 2:54 PM
    Message # 6896997

    I've a question, On the back of my Splitdorf ignition i 've a isolated point (see picture). It is just 1millimeter from my oil line. Is it possible that this gave my some ignition problems?

    Last modified: 09 Nov 2018 3:22 PM | Anonymous
  • 10 Nov 2018 3:53 AM
    Reply # 6898025 on 6896997

    Hello Theo , it can as this is the magneto cut out connection and takes a wire to the cut out button . Try moving the oil line away a little . Bets of luck , Ken

  • 11 Nov 2018 5:07 AM
    Reply # 6899094 on 6896997
    Tim Raindle (Administrator)

    Hi Theo, Ken is correct, if that stud is wired in it is the cut out . This works by earthing the mag when connected to a button on the handlebars. It should not touch anything. It may be worth checking to see if it is isolated from the case too, the stud should pass thru a small bakolite washer that prevents it grounding thru the case. Most Indian splitdorfs have this earth ( ground) connection on the side of the mag adjacent to the cap. It may also be worth checking the timing, in case you have a mag with a 45 degree cam. 

    Let us know how you go.


  • 11 Nov 2018 7:00 AM
    Reply # 6899178 on 6896997

    Normally, with a healthy capacitor one millimeter gap shouldn't be a problem. (EDIT: Now, that statement might give a too important role for the capacitor when it comes to prevent a spark to jump a fixed distance gap, whats matter is the voltage.) The voltage in the primary coil is comparative low, I think some 100-300 volt and not much amperage so it has a hard time jumping one millimetre of gap.

     When the points break, the current from the primary tries to keep flowing because of the self induction. That ionizes the air gap between the points, resulting in a conductive arc. With the capacitor across the gap, the primary coil unloads in the time it takes to charge the capacitor, in about 60 millionths of a second, supressing the arc effectively, and the main goal is to stop the primary current flow as fast as possible. So the points doesn't open much before the primary is emptied.  I use a thin paper between the points to set time of breaking. And before the current has build up again in the coil because of resonance, the points have had time to open enough to prevent a spark to form again. 

    That doesn't mean you couldn't have problem with that small distance to the oil tube, vibrations might short the points out randomly. 

    A sidenote. Primary coil inductance, magnet strength, engine max speed, in short how much energy the primary can contain is calculated and determine the size of the capacitor in mF. The coil and capacitor resonate with each other at a particular rate dictated in part by the capacitance in the capacitor. Too small capacitor and the current will spill over and arc between the points, too big and the charging of the capacitor is incomplete, too slow, resulting in low voltage in the secondary coil and that also changes the time the plug fires.

    The points need to open much more than the paper thickness, partly because coil voltage (electrons) is bouncing back and forth between the capacitor and coil and an arc can build up later in the sequense, and there is also the risk of the points bouncing that can fire a plug randomly.

    A second sidenote, there is a safety gap inside the magneto that is located in parallel with the coil secondary circuit. When secondary resistance becomes very high, such as when one of the spark plug wires is disconnected, the safety gap whose gap is much wider than a spark-plug gap, conducts the current to ground. This prevents breakdown of the highly-insulated magneto components.

    Last modified: 12 Nov 2018 10:19 AM | Carl-Erik Renquist
  • 19 Nov 2018 11:04 AM
    Reply # 6914187 on 6896997


    Thanks for your replies.

    It wasn't the problem that the oilline was too short from the Splitdorf point. Even when I reduced the space to a half millimeter the spark didn't interrupted. The problem was too much fuel in the combustion chamber. It faulted my sparks. When I set the carburator the right way the problem was solved.


    Theo Knoop

    The Netherlands

    Last modified: 19 Nov 2018 11:05 AM | Anonymous
  • 20 Nov 2018 3:05 AM
    Reply # 6915403 on 6896997
    Tim Raindle (Administrator)

    Good job , Theo. Fits the old adage, 90% of igntion troubles are in the carburettor, and 90% of carburation troubles are in the ignition system. 

    Sounds like you are getting to know your way around the bike, can take months to hunt out all the wrinkles. 

    If you send us a short report and a couple of pics of you and the bike for the wow, we will send you a marker plate enamel badge.

    Thanks for letting us know the solution.



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