What I learned shootin' the breeze

: I recently had my magneto in for a tune up and struck up a conversation with the fellow who did the work. He mentioned that mags the age of mine (1944 for a MM Z) had a certain life expectancy based on the length of service, and after they had been worked hard or long hours, the coils, points, condenser, etc. would wear out. That was old news, I thought, until he mentioned the behavior that a worn-out mag coil could produce. He said that as the coil inside the mag wore out, the insulation material would heat up during use and as the mag got hot, it would short out and kill the engine. The mag wouldn't run the engine until it cooled off, which it would then do for a somewhat shorter time than before. This would progressively get worse, until the insulation melted altogether and just quit. He said a lot of people would go nuts looking into the carburetor, governor, etc., while all the time it was actually the magneto coil. It seems logical that the coil on a distributor system could do the same thing.

: : I recently had my magneto in for a tune up and struck up a conversation with the fellow who did the work. He mentioned that mags the age of mine (1944 for a MM Z) had a certain life expectancy based on the length of service, and after they had been worked hard or long hours, the coils, points, condenser, etc. would wear out. That was old news, I thought, until he mentioned the behavior that a worn-out mag coil could produce. He said that as the coil inside the mag wore out, the insulation material would heat up during use and as the mag got hot, it would short out and kill the engine. The mag wouldn't run the engine until it cooled off, which it would then do for a somewhat shorter time than before. This would progressively get worse, until the insulation melted altogether and just quit. He said a lot of people would go nuts looking into the carburetor, governor, etc., while all the time it was actually the magneto coil. It seems logical that the coil on a distributor system could do the same thing.
I your spark is too weak to fire the engine, what is the problem with a magneto?

If what you're asking is "What is wrong with a magneto that is too weak to fire the engine", then the answer very likely rests with the coil. I no way do have any knowledge about these critters, but that is what I've come to find out. The coil generates the spark at a sufficient voltage to send an arc of electricity across the gap of the spark plug. If the coil isn't working properly, the spark won't do the job. Bear in mind there are other possible reasons for no spark. Neal Yerigan wrote an excellent book on the subject, and is without a doubt a leading expert on magneto problems. I don't have his e-mail address at hand, but he frequently reads the tractor talk board Ageless Iron. The link to this site is here -->

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