Coil polarity

If both spark plug electrodes are pointy then the polarity doesn't matter. The electrons will jump easier from a pointed electrode. The miniature spark plugs used on model airplane engine in the 1930's and 1940's have both electrodes pointed and the instructions written for how to hook up the coil say that the polarity doesn't matter. The polarity also determines which point has the metal eroded and which point has the metal deposited. This happens over time and happens more with a condensor that is not the correct microfarads. If the condensor is the right size there should not be any metal transfer between the points.
 
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nkaminar said:
If both spark plug electrodes are pointy then the polarity doesn't matter. The electrons will jump easier from a pointed electrode. The miniature spark plugs used on model airplane engine in the 1930's and 1940's have both electrodes pointed and the instructions written for how to hook up the coil say that the polarity doesn't matter. The polarity also determines which point has the metal eroded and which point has the metal deposited. This happens over time and happens more with a condensor that is not the correct microfarads. If the condensor is the right size there should not be any metal transfer between the points.
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This isn't really true in an old breaker type battery ignition system. The way coils are made governs the most efficient way to connect an ignition coil. The secondary coil is connected to only one of the two terminals of the primary coil circuit with the other end of that coil being the high tension output terminal to the distributor. Resistance is what makes the difference. If the polarity is off then the current pathway is a lot longer than if it is in correct polarity. Correct polarity will induce a more efficient spark than incorrect polarity. It will spark either way but the most efficient way is the best for a nice hot spark. The spark should travel from the center electrode to the ground electrode of the spark plug.

The condenser or capacitor's capacitance value it chosen to match the most efficient frequency of the coil's output capability during the induction cycle. It can vary a little and still function OK but it can't vary a lot or efficiency is degraded. A good condenser will almost eliminate any arcing across the points as they open. The smaller the amount of arcing, the longer the points will last.

The little NuRex tool is a very handy tool for quick ignition system checks. It works for both polarity checks and just plain spark checks.
 
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