Re: 2-stroke vs 4-stroke spark plugs;am I dreaming

[rvpapasso]

This whole current thing has been screwed up for centuries. I remember hearing in school (more memory flash backs?) that Benjamin Franklin assigned the terms positive and negative with regards to voltage and current flow and he got it backwards. Electrons, which is the actual current flow, go from negative to positive, the opposite to the convention we are all taught.

With tubes used in radios the object was to have a heating elements to “boil off electrons” as the old timers used to say. This cloud of electrons would then be manipulated by the anodes and cathodes to amplify, etc. That is the point of having the polarity assigned at a spark plug to boil off electrons.

The center electrode is hotter than the side electrode since the side electrode transfers heat directly to the head. The center electrode has a longer path to transfer the heat hence the length of the center electrode to the base of the spark plug defines the heat range.

The goal is to have the center electrode more negative than the side electrode so the electrons will flow from the center electrode to the side electrode. Given the center electrode is hotter than the side electrode the electrons are freer to “boil off” the center electrode increasing the ability to make a spark. In theory it makes sense.

However as pointed out many engines run with one cylinder’s center electrode negative and the other positive. My 1943 Harley works this way since the spark plugs are in series with the secondary of the ignition coil. One spark plug’s center electrode will have a positive potential and the other a negative potential.

The polarity may be more critical to prevent plug fouling in low tension ignition systems used on 2-stroke engines that use a heavy oil mixture. Certainly with modern high voltage ignition systems and lighter gas/oil mixtures on 2-strokes it doesn’t matter anymore.