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Mk3 Electric Starter.

Discussion in 'Norton Commando Motorcycles (Classic)' started by johnny Lagdon, Mar 16, 2019.

  1. johnny Lagdon

    johnny Lagdon

    Nov 18, 2016
    I am building a MK3 out of essentially spares and leftover bit and stuff I have accumulated over the years. I had a 4 pole prestolite motor from a harley modified to suit Norton. gathered all the info and gave to rebuilders .
    When I picked it up they confirmed it had been bench tested and rotated correct way for norton etc.
    I had completed the primary and hooked up a solenoid and battery etc and pressed the button and it just spun, in the wrong direction.so the sprag would not engage with the sprocket as reversed into free wheel mode.
    I took motor off and tried to spin the gear train and could get no movement either way by hand.I had negative to solenoid and then to starter motor. positive to earthon engine crankcase...any clues before I start again. can I bench test starter to check polarity? do I need a solennoid to do it?
  2. kommando


    May 7, 2005
    No need for a solenoid to test but have the starter gripped well as it will jump with power applied. Don't have any flammable liquids around as sparks fly as you touch the final lead. Did you check the starter had not already been converted, if it had then it may now be back to where it started before the previous conversion.
  3. jimbo

    jimbo VIP MEMBER

    Sep 25, 2004
    I am pretty sure you can take the brushes out of their holders move them all ccw one holder over, and reinstall them. that will reverse the motor. Its fiddly for sure.
  4. Madnorton

    Madnorton VIP MEMBER

    Jun 9, 2008
    The really, really important bit in the OP is that the gear chain will not turn in any direction - strip the primary now, do not fit the motor until you have done so.
    It is the the choice of a primary rebuild, or an expensive primary rebuild, and / or even trying to find a crank DS end.
  5. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Nov 20, 2004
    If the starter motor polarity is reversed it will rotate in the same direction. To reverse the rotation the brushes must be moved as jimbo says.
  6. Ron L


    Feb 27, 2004
    I agree. It could be the anti-kickback device is slipping and needs to be tightened or replaced or the sprag clutch has broken the retaining ring. Make certain the sprag clutch is installed the correct way around.
  7. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Nov 20, 2004

    The OP stated that when the motor was used the drive turned "in the wrong direction"........

    ....therefore unlikely the anti-backfire device would slip in that situation. If it did then the loud rattling noise the AB device makes as it does so would be unmistakable.
  8. KiwiNeill


    Jul 25, 2011
    Jonny Lagdon
    with the starter motor removed, you should be able to turn the large gear wheel (which fits inside the sprag) freely in a clockwise direction by hand.
    It should lock as soon as you turn it anti clockwise, or the direction of normal engine rotation.
    Both ops are easily checked by hand and correct rotation readily established.
    If the gear wheel turns or locks in the opposite direction, you probably have the sprag fitted the wrong way around.

    If it spins freely in both directions the sprag has flipped back the wrong way and needs replacing. I had this problem on a near new sprag in 2015 and took it back to AN who checked and replaced it straight away, the replacement lasting four years and over 10,000 miles with 100% e start on a healthy 850.

    This should all be checked and tested by hand before finally fitting the starter motor. If the starter then spins in the wrong direction, that is a different problem and the brushes will needed to be rotated 90°

    I have just fitted a new sprag, sprocket and chainwheel assembly along with a duplex primary using these exact proceedures. Worked freely by hand in the right direction and fired up perfectly with starter motor fitted.
    I set the timing at 28° using the crankcase slot on the lower right side under the ignition cover for accuracy rather than the primary case indicator. Trispark ignition and Boyer Micro Digital Power backfire free with this method.

    Old Britts have an excellent article on e start assembly, saved me much time over the years bless them, and there is also a link on adjusting the backfire device:
    Last edited: Mar 17, 2019 at 12:14 AM
  9. johnny Lagdon

    johnny Lagdon

    Nov 18, 2016
    Thanks for all replies.
    I am going to strip the starter gear train again as with starter and idler removed, i should be able to move the gears by hand as spragg should not be engaging.
    Sprag is brand new 18tooth, and worked perfectly when i tried before fitting sprocket and large inner gear. spun one way but not other as it should.
    if no success will get stater brush position double checked.
  10. johnny Lagdon

    johnny Lagdon

    Nov 18, 2016
    I removed the stator, rotor and no change. Loosened the outrigger plate the stator mounts on man suddenly everything was as it should be, reverse the large gear on the spragg and sprocket. nipped it up but not to full tight and started to get harder to move.
    further examination required.
  11. johnny Lagdon

    johnny Lagdon

    Nov 18, 2016
    after much trial and error it is the stator mounting plate causing the jamming problem. after repeated tightening and finessing of all bits, the plate is a little warped, and this was putting a side load on the backfire overload shaft that mounts in it as well. Now for the starter motor.
  12. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Nov 20, 2004
    Another member had what seems to be a similar problem recently.
  13. jan nelder

    jan nelder

    Feb 18, 2018
    for the new uprated starter motor from Norvil : it spins SAME way for either polarity of connection. Useful as I changed to negative earth!

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