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John Deere B 1942 No Spark Bad Magneto/Distributor

E

Evan KG

New User
Hello,

I have a 1942 B John Deere and for some reason it cannot seem to keep any spark. Originally it came with a magneto and we had two magnetos rebuilt and both of them lost their spark when we installed them on the tractor. In an attempt to fix the problem, I switched to a distributor with the electronic ignition. 3 months later, I am back to having no spark. We did convert the tractor to negative ground and added a Fleet Store (Chevy) one wire alternator and it has bored out oversized pistons the same size as a John Deere 520. Other than that, the tractor is original.

I am all out of ideas and any help is greatly appreciated.

Thank you.
 
Welcome to YT. I don't understand that 2 rebuilt magnetos lost their spark when you installed them on your tractor. Are they the correct type? There are long and short lug versions of them. Are they the correct rotation, and do you hear a distinct snap when it trips? And are you sure you didn't have the kill wire going to ground? That will keep it from firing. You may already know these things, but I do not know your level of experience on these. I cannot be of any help on the distributor, I prefer a magneto
 
My experience with 2 cylinder John Deeres is pretty minimal. I've only been working on them for a few years.

The tractor had short lugs on the magneto and that is what we used for both magnetos and the distributor. The first magneto was a Wico 1042 and I forgot what the other magneto was. Ended up giving both magnetos away and all I have now is the distributor with the electronic ignition. The weird thing is the tractor would run great for a few months with the new magneto or distributor and then there would be no spark.
 
Need to do some basic troubleshooting.

Is there 12v to the primary side of the coil AND to the ignition module in the distributor?

Put a test light between the - primary terminal and ground. Crank the engine through, the light should flash off and on as the engine turns. If this is happening, and no spark from the coil, the coil is bad.

If no flash, check the wiring from the module to the coil. Light steady on is an open circuit, steady off there is a short to ground. Also check the mechanical function of the distributor, that it is turning, and all components of the conversion kit are in place. Be sure the distributor is grounded.

The main reason conversion kits fail is the wrong coil. It is critical to have the correct coil or coil/resistor combination. Out of circuit, across the primary terminals needs to be about 3 ohms, either directly across the terminals or with the resistor in series.
 
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