Practical points on plug setting

When setting the gap (left), pressure should not be applied to the central electrode. The feeler gauge (right) must be kept square with the plug points to ensure a correct reading
A useful tip known to plug specialists is to true-up the sides of the electrodes lightly with a small, fine-cut file, to restore the sharp corners that existed when the plug was new. This will considerably reduce the voltage needed to produce a spark across the gap.
The threaded portion of each plug should be cleaned with a stiff wire brush and a smear of graphite grease placed on the threads. This will ensure that the plug will tighten down easily and facilitate removal when the next cleaning and adjustment is due.