Spark Plug Fixture (39D18 Plug); Wiring - Test Setup - Piper Navajo PA-31 Service Manual

.125
IN. S.A.E. 1010-1020
STEEL
ROD
.125 IN.
DIA.
PIPER NAVAJO SERVICE MANUAL
INTERNAL
TEST
CIRCUIT
EXTERNAL
TEST
CIRCUIT
I
MOMENTARY
SWITCH
BATTERY
AMMETER
VOLTMETER
I
VIBRATOR
THREAD
18 M.M. - 1.5 M.M.
PITCH
S.A.E. SPARK
PLUG STANDARD.
ILTER
RESISTER
NOTE: DIMENSION
A VARIES
WITH LENGTH
OF SPARK
PLUG.
GAP
OF ALL SPARK
PLUGS
+0
IS TO BE 3/16 - 1/32
Figure 13-21. Spark Plug Fixture (39D18 Plugs)
TOTAL
RESISTANCE
A TO B MUST NOT
EXCEED
0.3 OHMS.
Figure 13-22. Wiring - Test Setup
b.
Installation:
1.
Place the ignition assembly in position on the heater jacket, with the high-voltage
cable
facing the spark plug end of the heater.
2.
Install the four screws and tighten the screws securely.
3.
Carefully connect the high-voltage lead to the spark plug.
4.
Connect the primary lead to the primary terminal on the ignition assembly and tighten the
nut securely.
5.
Check for proper heater operation.
13-30. TESTING IGNITION UNIT. The ignition unit does not require complete overhaul. The following
test will indicate whether or not the unit is operational and whether the vibrator should be replaced
before
reinstallation in the aircraft. The following equipment is required to test the components:
a.
A battery that will supply power at approximately 24-volts DC.
b.
A voltmeter with a range of 0-30-volts.
c.
A lead from the battery to the ground electrode on plug (IOD22) or test fixture install on plug
(39D18) in which is included an ammeter with a range of 0-3 amperes and a
normally open,
momentary-closed switch. The total resistance of the lead including the ammeter and switch
must not
exceed 0.3 ohms
d.
A spark gap of 0.050 to 0.060 inch is required on IOD22 spark plugs which include the ground
electrode loop. The proper gap for the 39D18 plug is 0.156 to 0.188. A convenient means
of arranging the
correct spark gap for 39D18 plugs is to install the spark plug in a test fixture arranged to
provide a ground
electrode and a spark plug gap as noted above. (Refer to Figure 13-21 for information on
fabrication of this
fixture.)
Reissued: 10/12/79
HEATING AND VENTILATING SYSTEM
5C2