‘42 A magneto/timing bhelp

Farmall Super A, AV, 100, 130, & 140 1939 - 1973
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Tractors Owned: 1970 IH Cub with 5 implements
1966 140 with Manuer bucket fast hitch & 3 impliments

‘42 A magneto/timing bhelp

Postby M6Scout » Wed Sep 16, 2020 3:01 pm

Hi all,
My A starts up flawlessly!
My helper shut it down came back it won’t start no spark from the magneto wire.
Anyone have a service manual on these Or advice on possible issues.

He told me sometimes they jump time, so he moved the roto several times and L/R.

So how do I time this puppy


Jim Becker
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Re: ‘42 A magneto/timing bhelp

Postby Jim Becker » Thu Sep 17, 2020 12:23 pm

Lets see if I can help. First off, I'm making 2 assumptions. If either is wrong, you will need to time it from scratch.

1) There was nothing wrong with the timing before your helper got his hands on it. I keep hearing about an engine "jumping time". I have never seen it actually happen. The only time I can imagine it actually happening is if a worn timing chain (the A doesn't have one!) jumps a cog on a sprocket. If that happens, messing with the magneto won't fix it. The problem is deeper.
2) Nobody has removed/loosened/rotated the magneto housing where it attaches to the engine. If they haven't, the fine timing adjustment is still preserved.

If either of these assumptions is wrong, you will need to set the timing from scratch and these instructions won't do it. Otherwise:

- Under the cap and rotor is a small cover held by 2 screws. Under the cover is a pair of gears. They need to be meshed so the pinion tooth with the corner clipped off lines up with the "R" in the gear of the distributor spindle. Install the cover and the rotor.
- Turn the engine to approximately top dead center on cylinder 1. Remove the #1 spark plug and crank the engine by hand until a thumb feels compression on #1. Continue to turn until the impulse clicks. If the impulse doesn't click, It needs fixing, which is another whole task and may explain why your tractor wouldn't start.
- Since the driven gear in the magneto is twice the size of the pinion, there are actually 2 ways it could be installed with the marks aligned. The rotor should be pointing towards 1 o'clock (viewed from the tractor seat). If it is pointing towards 7 o'clock, remove the gear cover again, remesh the gears with the distributor spindle exactly 180 degrees from the current position.
- Finish assembling the magneto. Reinstall the #1 spark plug wire with the wire at 1 o'clock in the cap and going to cylinder 1. The other wires should go to cylinders 3, 4, and 2 as you go clockwise around the distributor cap.

You should now be back where you started and can start to figure out why you have no spark.

First I would disconnect the grounding wire from the side of the magneto. A shorted wire or ignition switch could be the problem. Next, I would go back into the magneto and check the ignition points for clean contacts and proper gap (.013" with the breaker rub block on the high point of the cam).

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