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Allis Chalmers Discussion Forum

C Allis Magneto-Spark on only 2 cylinders

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Author  [Modern View]

07-27-2008 14:19:00

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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.

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Steve in NJ

07-30-2008 03:36:21

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 Re: C Allis Magneto-Spark on only 2 cylinders in reply to JordanNC, 07-27-2008 14:19:00  
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

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07-28-2008 20:48:28

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 Re: C Allis Magneto-Spark on only 2 cylinders in reply to JordanNC, 07-27-2008 14:19:00  
Are you sure that it's not a John Deere mag?! LOL

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Kentb of SWMO

07-27-2008 15:06:45

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 Re: C Allis Magneto-Spark on only 2 cylinders in reply to JordanNC, 07-27-2008 14:19:00  
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.


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El Toro

07-27-2008 14:31:16

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 Re: C Allis Magneto-Spark on only 2 cylinders in reply to JordanNC, 07-27-2008 14:19:00  
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

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Today's Featured Article - The Mud Daubers and the Old John Deere - by Jon Zehnder. I have a 1941, John Deere Model A tractor I have owned for about a year and a half. This is my first (in case my wife reads this, "FIRST") tractor and it has been a learning experience. After considerable advise and assistance from local tractor nuts and the forums of Yesterday’s Tractors, I had finally got it running pretty well. I have tuned it up, overhauled the carburetor, installed a borrowed, rebuilt magneto, installed a new Power-Trol, patched the radiator, installed new front wheels a ... [Read Article]

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