Spark Plug Gap Adjustment (39D59 Heater) - Piper Navajo PA-31 Service Manual

PIPER NAVAJO SERVICE MANUAL
385
0.050 to 0.060 inch
BEND TO ADJUST
CENTER ELECTRODE
GROUND ELECTRODE
Figure 13-19. Spark Plug Gap Adjustment (39D59 Heater)
NOTE
If the spark plug fails to clean up properly and/or if electrodes are
badly eroded, it should be replaced.
c. Spark Gap Check and Adjustment: (See Figures 13-19 or 13-20.) A spark gap of 0.050 to 0.060
inches must be maintained on the 10D22 spark plugs. The 10D22 plugs are identified by the ground
electrode loop per Figure 13-19. The 39D18 spark plugs require a gap of 0.156 to 0.188 inches. The 39D18
plugs are identified by the center electrode without the attaching ground electrode per Figure 13-20. The
gap should be checked any time a plug is replaced or at the time of heater overhaul. A spark greater than
that specified can shorten the life of the ignition assembly. Method I noted below is the gap setting
procedure for the 10D22 spark plugs. Methods II and III are for the 39D18 spark plugs. Method II is
recommended when the heater is being overhauled and before the installation of the fuel nozzle. Method III
is suitable for checking the gap through the spark plug well when the heater is not disassembled.
Method I: (10D22 spark plugs only)
1. On the 10D22 spark plugs the gap is set by carefully bending the ground electrode
until a 0.055 inch feeler gauge can be inserted between the end of the center electrode
and the ground electrode.
2. Do not bend the center electrode.
Method II: (39D18 spark plugs only)
1. Using a 5/32 inch drill (0.156) or a piece of 5/32 inch rod, reach through the opening
in the combustion head (fuel nozzle location) and find the ground electrode. (It is
welded inside the head.)
2. Move the drill along the side of the electrode on the spark plug side. (Movement should
be from the outer edge towards the center.) The drill or rod should just pass through
the spark plug gap opening. Should the drill fail to pass through this opening, the gap is
too narrow. If it passes through too freely, the gap is too wide. In either case, it will be
necessary to bend the ground electrode in the direction required. This may be done by
removing the spark plug and reaching through the opening.
3. Recheck the gap after repositioning of the ground electrode.
Reissued: 10/12/79
HEATING AND VENTILATING SYSTEM
5B23