The following was extracted from the September 15^th, 1961 issue of the Australian Fortnightly Motor Manual and provided by Owen Gregory.

“Filing System” for Sparking Plugs

From K. I. G. technicians comes a tip worth remembering when servicing sparking plugs.

To get that “new plug” feeling, they advise, it is well worth while lightly filing the end of the overhead earthwire and the top of the central firing point to restore the sharp edges which existed when the plug was new, but which would have become rounded due to the hot gases and the burning effect of the spark.

Amongst other factors, this sharpness of the electrodes has a considerable effect on the voltage necessary to spark the gap, and it is a fact that the lower this sparking voltage the easier becomes engine starting and the greater the measure of freedom from misfiring under running conditions. In this context, the increasing voltage consequent upon the rounding off of the sharp edges with use, joins forces with the short circuiting effect of deposit on the insulator to cause misfiring of a dirty plug, the increased width of spark gap, also due to burning, further aggravating the effect.

Servicing a plug simply by cleaning and re-setting the gap, therefore, is only two-thirds of the way back to the nearest approximation of a new plug. Filing up the points provides this third step, and except where plugs are on their last legs imparts to a serviced plug just that little bit extra which makes its performance surprisingly near to new.

Pub chairman’s note: A procedure not much performed today, I expect.