Adjusting the Plug Gaps

After the plugs have been cleaned and the points trued-up as just described, the gap should be adjusted by bending the side electrode only. One of the inexpensive combination gauges and setting tools sold by plug manufacturers is a worthwhile investment. If an improvised method is used (Fig. 35) make sure that no leverage is exerted against the central electrode; otherwise the internal insulator will probably be cracked, rendering the plug useless.
The recommended gap of 0-025 in. (25 thousandths of an inch) will give best results under all normal conditions. If the plugs are prone to oil-up, a smaller gap may be tried—say, 0-020 or 0-022 in.—but this must be regarded as a palliative rather than a cure. If the prospect of an engine overhaul is rather remote, the use of a spark intensifier, as described on page 91, will usually enable the normal gap to be restored without the risk of misfiring or difficult starting.