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C Allis Magneto-Spark on only 2 cylinders

A

Anonymous-0

Well-known Member
I have a '47 C with a Fairbanks-Morse magneto that only has spark on two cylinders. I thought this would be a cap or rotor problem so I replaced both the cap and the rotor (not with a new one, but from another running tractor). I still have the same problem. No spark on the same two cylinders. I have checked the plugs and wires on the two problematic cylinders to see if they work, and they do. Does anyone have any recommendations as to what I should check next? Thank you.
 
Have you checked the lobes on the mag for being worn flat? See if there's any slop in that mag's shaft with the lobes. Hal
 
Has someone installed one of the solid-state chip that replace the points and condenser? If so this will cause it to fire on anly two cylinders. It will fire, skip, fire and skip.

Kent
 
The problem could be a very weak magnetic field at the magnetic rotor. If that is the problem, re-magnetizing the rotor assembly is the fix. I've had mags come in for repair that had the problem, when I first ran them on the bench, and after a good rebuild and re-magnetizing the rotor assembly, the fire is back at all four holes with a vengence. Another problem F/M had with its early version Mags is the tar-taped coil that was used. These coils would "leak" to where stray spikes would ground to the inside of the Mag housing and either kill the engine or kill a cylinder or two. HTH
Steve@B&B
 
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