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For the preservation and enjoyment of 1928 to 1931 Indian Scout Motocycles
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Magneto Gear Removal

  • 25 May 2017 5:54 AM
    Message # 4851814

    Hi anyone got a good tip for removal of the drive gear from my Bosch mag?

    The mag is still on the engine, but there doesn't seem to be much space around the gear for a gear puller, and I'm not keen to thrash the end of the magneto for fear of breaking the crankcase.

    The engine probably hasn't been apart for 50 years so just trying to be careful.

    Any tips gratefully received! Thanks

  • 26 May 2017 1:31 AM
    Reply # 4853640 on 4851814

    First check the shaft and gear if it wobble ever so slightly, and if it show difference in gear lash with an indicator clock and feeler wire. The magneto shaft end does bend easily, and the gear can have a fault in it so it is out of center. That has impact later when you try to adjust the gear play when mounting the magneto. The gear lash HAS to be quite large, a tick-tock has to be heard in all positions around the revolution when you rock the gears. Because of the tiny bearings, the magneto do not fancy unequal gear lash and can not take sustained side load from the gears. 

    Don't be tempted to pry or pack something behind the gear in trying to tap the gear loose from the shaft. The threads on the shaft (if they haven't been damaged and cut off already) are soft and fragile. And to that, the aluminium cam cover is fragile and/or bend easily.

    Best is to make a designated puller for it, larger of course and maybe in 2 halves, but similar to that one you need for the pinion gear. The puller doesn't need to be overly strong if it grabs a large portion of the circumference. A modified common 2-3 leg puller with narrow hooks at the ends can be risky and break off a cog, best is to make a puller that has as wide contact area as practical.

    Using heat is a bit dangerous depending on what heat source you use, because the gear is heat treated, and that also involve some tapping on the shaft. The bearings in the magneto are very small and do not sit directly in the housing, they are shimsed with some electric current isolating wax coated paper! So they can't take hard knocks or much heat. 

    Of course when you have put tension on the puller, a light tapping on it may be needed to release the gear, but to ease on the impact on the bearings, I pull with my hand on the puller at the same time I tap on the screw. I don't know if it make any difference at all at the bearing end, because in a healthy Bosch, the shaft end play should be set to zero, but I feel like I care.. :-)

    Last modified: 26 May 2017 2:16 AM | Carl-Erik Renquist
  • 26 May 2017 4:44 AM
    Reply # 4853778 on 4851814

    Hi Carl.

    I tried a friends puller, but the legs were too thick to get between the casing and the gear. I'll buy a thin leg puller from good old ebay and grind the thing down until it fits.

    I would have thought that since 1928 someone would have designed and marketed some special tools for just this job ... Maybe a bit late now though.

    Cheers Mick

  • 26 May 2017 11:27 PM
    Reply # 4855030 on 4851814

    One way is to make a simple tool additive that can be used with a common 2 legged puller. Make it on a lathe is ideal, but also without a lathe it is possible to make one. What I describe is just a suggestion and one way of doing it...

    Take a short piece of pipe (40-50mm long) slightly larger than the gear. Then weld a washer at one end. Enlarge the hole in the washer so the remaining lip or rim is narrow enough to not damage the oil slinger on the backside of the magneto gear. Maybe 5-6mm wide. Inside needs to be level and smooth to avoid damage of any cog. At the other end of the pipe, drill and file suitable holes for a 2-legged puller at the exact same height. Then part the tube longitudinal. 

    Slip the parts in on the gear, and clamp them together with a rubber band. Hook the 2 legs of the puller in the pipe holes and pull. Ideally you have also made a solid extender, threaded on the magneto shaft about the same length as the pipe. 

    Last modified: 26 May 2017 11:35 PM | Carl-Erik Renquist
  • 01 Jun 2017 6:40 PM
    Reply # 4875542 on 4851814

    OK Success! Ebay purchase of a "Thin 2 Jaw Bearing Puller" No 5123 made by US Pro tools did the job with a bit of modification. The legs are quite thin, although not thin enough to get between the gear and the case - a bit of judicious grinding sorted that out. The material of the puller is surprisingly hard considering the low price. Anyway gear now off ... time to get the magneto rebuilt!

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