[johnsjmc]

The gap will eventually grow from normal erosion of the electrodes.This used to be about .001 per 1000 miles with leaded gas. The gap growth is much less with unleaded The high output ignition systems will compensate for the wider gap by producing a higher voltage to continue to fire the plugs. If the gap gets too large the high voltage can leak out of the spark plug wires to ground especially in damp weather.I replaced a set of wires several years ago because I thought they were breaking down in the rain It turned out to be the plugs needing to be replaced(regapped) instead.