MTFCA Forum

I'm getting ready to clean up the Edison 14 spark plugs that were in my 15 runabout before I removed them before the restoration. Two of them measured about .030 gap, with the other new more because the electrodes were corroded a bit. Is .030 gap correct for the Edison 14 plugs, and if not, any suggestions for what I should use after I get them cleaned up?

Thanks,

Neal

I run 0.030 on mine with no problems. My car is missing its magneto and running a Truefire ignition.

My Edison 14's use a 0.025" gap and run clean, with no power problems. There's a set of Edison 14s in Thomas Alva Edison's 1922 touring car at the Glenmont garage in West Orange that we installed and that engine runs and purrs like a kitten

With a few rare exceptions (like sheltered ring gaps), spark plug gap is a factor for the ignition system, the power (voltage versus rpm and other factors) and coil capabilities etc. Spark plug gap shouldn't vary more than about one thousandth from one brand and/or version to another (and that one thousandth variance would be due to the "hotness" of different plugs). Wider gaps do give a hotter spark than smaller gaps. But wider gaps also greatly increase the likelihood of coil and/or point failure.
A model T stock (or mostly stock) ignition, the commonly given spark plug gap is between .030 and .032. Personally I prefer .028 because it is slightly easier on my hundred year old coils, and doesn't seem to affect performance noticeably.

For comparison's sake. A model T using a Bosch DU4 magneto without an impulse for starting, the recommended spark plug gap is .018 to.020. The reason for a much smaller gap is that the DU4 puts out too low a voltage at hand cranking speeds to start the motor (I know this, because years ago I had one and tried .030, no way was it going to start, besides the era DU4 manual I later read said so!). At higher speeds, the magneto puts out much higher voltage, and the spark is hotter than stock ignition in spite of the smaller gap. Even if one has an impulse, or a starter that will spin the engine fast enough to start the car with an .030 gap? The gap should still never be more than .022 because at higher speeds, the higher voltage across the resistance of the wider gap has a nasty habit of burning out the magneto (sometimes the capacitor, sometimes the armature itself, I have seen it).