21-40-00 Page 21-30 Revised: February 28, 2002
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A. Disconnect the primary wire from the primary terminal of the ignition assembly.
B. Carefully unscrew and disconnect the high voltage ignition cable at the spark plug. Exercise care to avoid fouling or damaging the connector.
C. Remove the four attaching screws and lift the ignition assembly off the heater jacket.
2. Installation: (Refer to Figure 21-18.)
A. Place the ignition assembly in position on the heater jacket with the high voltage cable facing the spark plug end of the heater.
B. Install the four screws. Tighten the screws securely.
C. Carefully connect the high voltage lead to the spark plug.
D. Connect the primary lead to the primary terminal on the ignition unit and tighten the nut securely.
E. Check for proper heater operation.
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:
1.
A battery that will supply power at approximately 14 volts DC.
2.
A voltmeter with a range of 0-15 volts.
3.
A lead from the battery to the test fixture 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.
— CAUTION —
WHEN TESTING AN IGNITION UNIT, DO NOT USE A SCREWDRIVER
AS A SUBSTITUTE FOR A SPARK PLUG AND SPARK PLUG FIXTURE.
4. A spark gap of 0.187 inch (plus 0, minus .030). A convenient means of arranging the correct spark gap is to install a spark plug, P/N 39D18, in a test fixture arranged to provide a ground electrode and a .187 inch spark gap. (Refer to Figure 21-10 for information on fabricating this fixture)
— Note —
Any one of several spark plugs may be used with the spark plug fixture detailed in Figure 21-10. However, the “A” dimension in that sketch must be varied with the length of spark plug electrode to provide a gap of .187 inch for all spark plugs.
5.
The high tension shielded ignition lead between the ignition unit and the spark plug is a part of the cover assembly.
6.
Arrange the test equipment as shown in Figure 21-11.
OPERATIONAL TEST OF IGNITION UNIT.
1.
Close the momentary switch and read the voltmeter and ammeter. Release the momentary switch immediately.
2.
The amperage reading at 14 volts DC must be 1.50 ± 0.25 amperes.
21-40-00 Page 21-31 Revised: February 28, 2002
VIBRATOR.
The vibrators should be replaced after 250 hours of operation. This schedule applies equally to vibrators installed in new units as well as new vibrators installed in ignition units that have been in service.
VIBRATOR REMOVAL AND INSTALLATION. (Refer to Figure 21-13)
1.
Remove the clamp.
2.
Remove the vibrator from the ignition unit; it may require a slight back-and-forth movement to remove it from the unit. A piece of masking or friction tape around the exposed portion of the vibrator will help to grip the vibrator for removal.
3.
Install the new vibrator with the index marks aligned. The connector pins on the vibrator can be felt entering the pin sockets in the vibrator socket, then press the vibrator fully and firmly into position. Secure with the clamp.
— Note —
If replacement of vibrator fails to correct operational failure, further disassembly and inspection may be required.
21-40-00 Page 21-32 Revised: February 28, 2002
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