Timing trouble with farmall M magneto H4

Posted by oldtractor123 on August 31, 2013 at 08:28:02 from (108.59.112.204):

Having trouble re-timing my Farmall M magneto after catastrophic failure.

Cruising along in 4th gear my M let out a big backfire and just stopped running. Won't start. Got gas ? YES ! Doesn't even pop.

Towed it home :cry: and pulled off the magneto rotor cap. Cranked a couple times. The rotor isn't turning !?!?!?

Pulled off the magneto.

The magneto drive on the tractor is turning.

But the magneto is locked up tight.

Looking into the magneto drive end I see what looks like part of a 1/4" screw jammed between the impulse unit and the housing.

I was able to knock out the screw piece and then removed the impulse unit nut. Pulled off the impulse unit and removed the screw pieces. I see there are 2 missing screws. These are the 1/4 20 counter sink screws that hold on the mounting flange housing assy on.

So replaced the screws and reinstalled the impulse unit.

Now of course I can't seem to get the magneto timed properly.

It's running but now wants to backfire through the carb and overheats very quickly. Doesn't seem to be enough slot space to get it timed right.

So what just happened ??? Did the drive gear slip a tooth or two ?

Or am I just not getting the timing set right ? Got the number one piston at TDC on compression stroke. Rotor cap strip is close to sparkplug wire #1.

No matter what I do I can't get the impulse to fire at TDC.

So where do I go from here ? Pull the tractor mag drive unit and bump a tooth or so ??

Getting into uncharted waters here.

Thanks for any help.

Dennis

PS first post.

Replies:

• Re: Timing trouble with farmall M magneto H4 oldtractor123 11:22:08 08/31/13 (3)
  • Re: Timing trouble with farmall M magneto H4 Janicholson 15:32:36 08/31/13 (2)
    • Re: Timing trouble with farmall M magneto H4 El Toro 16:27:27 08/31/13 (1)
      • Re: Timing trouble with farmall M magneto H4 oldtractor123 14:09:40 09/10/13 (0)
• Re: Timing trouble with farmall M magneto H4 Bob 10:20:01 08/31/13 (1)
  • Re: Timing trouble with farmall M magneto H4 oldtractor123 10:28:09 08/31/13 (0)
• Re: Timing trouble with farmall M magneto H4 El Toro 09:18:07 08/31/13 (5)
  • Re: Timing trouble with farmall M magneto H4 oldtractor123 09:58:02 08/31/13 (4)
    • Re: Timing trouble with farmall M magneto H4 Janicholson 12:15:28 08/31/13 (3)
      • Re: Timing trouble with farmall M magneto H4 oldtractor123 13:22:18 08/31/13 (2)
        • Re: Timing trouble with farmall M magneto H4 Janicholson 14:25:49 08/31/13 (1)
          • Re: Timing trouble with farmall M magneto H4 oldtractor123 14:40:35 08/31/13 (0)

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