Two broken magneto shafts in two days

jasonag69

New User
We have been trying to get a 39 JD B started after several years of sitting and we were working on getting spark from the magneto, we finally got it...
we got first spark and tractor started
-Ran tractor for 20 minutes in driveway no issues.
-Put in garage noticed water in oil
-Changed oil and filter with new detergent oil.
-Tried to start and started for 2 seconds and died never to spark again. Plulled magneto and found broken shaft.
-Replaced broken mag shaft with used working shaft assembly and tractor started and ran for 5 minutes and mag shaft broke again while I was gently pulling forward

Why does the shaft break in the two magneto's after only a few minutes of operation, both had free spin movement and not much play side to side? The shaft broke in the middle and sorta look like it was twisted apart. Any ideas?
 
Are u using long lug mag on short lug govenor coupler? Additionally even if using the correct lug mag, you need to be sure your using
gasket(s) of sufficient thickness to prevent overly preloading the couplers and causing them to bind.
 
Are the bearing in the magneto good? They need to turn
free and smooth. If the rear bearing is rough. It can lock
up and stop turning.

I had a Wico XH do that on a Farmall M once.
 
I was suspecting the governor also the governor shaft is rotating slightly off center, not sure if it is bent or a bearing. Being new to this I just thought it was ok for an old tractor.

Bearings seem find in both mags before I put them in. I am using the short lug mags but did not have any gaskets on either one of them. I also torqued them down pretty good.

With the slight off center in the governor shaft and the no gasket could that be it?
 
I really don't see how a gasket could help. I don't have
flange gaskets in any of my tractors.

I wouldn't torque mag mounting bolts.

The governor drive should not be off centered.
 
Thanks, I would tend to agree with what you have said. Unfortunately, we are very suspect now of the Governor shaft or bearings. Looking into a possible rebuild.
 

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