Allis B Magneto - Fairbanks Morris J

ErnDog50 · Jul 6, 2015

I have a 1940 Allis Chalmers B which has always run great, that is until this spring. I am not getting any spark so I decided it must be the magneto. Before pulling the magneto I looked at how it was wired. Strangely enough, the number 3 cylinder is plugged into the number 1 hole on the magneto, the number 1 cylinder is plugged into the number 2 hole, the number 2 cylinder is plugged into the number 3 hole and the number 4 cylinder is plugged into the number 4 hole. This keeps the firing correct; 1, 2, 4, 3. Does this mean that someone timed the magneto by having cylinder 3 at TDC, set the magneto accordingly and plugged the wires in from there? Confused? I know just enough about this to be dangerous.

steve(ill) · Jul 6, 2015

Yes, you are right. The mag rotates in one directions, as long as you keep the wires in the right order, you can start at any point with #1. When the #1 cylinder comes up on compression "they" looked to see which mag wire was about to fire and called that #1.. This happens a lot on the old tractors. Does not effect the running by changing location, as long as the order is correct.

old · Jul 6, 2015

There are 2 common mags that can be on that tractor. I have the manual for both in this computer so if you send me an e-mail an tell me which one it is I'll send you the manual so you can fix the mag

ed in cny · Jul 6, 2015

One of the B's I have had that simular issue and was indeed firing incorrect. After diagnosing the issue I found that
someone had taken the from end of the engine off and the timing marks were 180° off from where they were to be. The
tractor would run fine but wouldn't start that easy. After a good raspberry on my leg I had, had enough so I correct
that issue. I doubt that's your problem though but just said that to say they will run in other configs without much
issue. Run great but now has other issues that I am working on. Seems a never ending job to keep these B's running and
running right.

ErnDog50 · Jul 7, 2015

The mag is a Fairbanks Morris J

ErnDog50 · Jul 7, 2015

Thank you so much, I am glad to have this confirmed. I have never seen an old tractor where the number 1 cylinder spark plug was wired into anything but the number 1 on the mag and I was at a loss for awhile. However, logic prevails and it made sense to me that other arrangements would work following the process you described as long as the firing order is correct.

ErnDog50 · Jul 7, 2015

It seems to me that keeping any of these old machine running smoothly is a challenge. I have a lot of different brands and that makes it more difficult. However, I grew up on a 1937 Allis WC and that is something that never leaves you. I still have that old tractor. It has a full set of cultivators mounted on it.

old · Jul 7, 2015

Ah but Fairbanks Morris makes many mags but I am guessing from what you say it is a J-4 I have that manual and all it takes to get it is sending me an e-mail. My e-mail is always open on here

Allis B Magneto - Fairbanks Morris J

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