[Farmall] M magneto

[Robert L. Holtzer]

On 7/10/2010 5:11 PM, William Ransom wrote:
> I last had the Farmall M running in 2006. When I tried to start it in 2007 and 2008, it seemed to be trying to start, but it wouldn't actually run. Last year, I tried again to start it, and that time the engine didn't seem to fire at all. Today I decided to check the magneto. When I checked it before (by turning the fan by hand with the end of the coil wire close to one of the clips that hold the distributor cap on), I would usually get a spark, which often looked orange or white. Today, I didn't get any spark, so I decided to take the magneto apart. First I measured the resistance of the coil and found it was about 12k ohms (between the terminal on top of the coil and the outside of the magneto). Then, I measured the resistance across the points and found that it was about 1 ohm, whether the points were open or closed. At first I thought maybe the condenser was the problem, so I tried removing the condenser, but that didn't make any difference. Then, I disconnected the coil!
>    from the points, and with the coil disconnected, the resistance across the points still seemed to be about 1 ohm with the points closed, but nothing conducted any electricity across the points when they were open. After I disconnected it, the resistance between the red wire on the side of the coil (the one that's supposed to go to the condenser and points) and the outside of the magneto seemed to be about 1 ohm, so I think there must be a short inside the coil that shorts across the points and condenser. Do you think the coil needs to be replaced? How do you remove the coil?
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Resistance across the closed points should be zero.  My first guess 
would be that the points are non-conducting and you are measuring coil 
resistance.  Resurface the points with a point file or non-carborundum 
sandpaper and see what happens.  If that doesn't help then on to more 
major considerations.

Bob Holtzer