Piper SEMINOLE PA-44-180, Maintenance Manual

Page: 134 / 881

B. Unscrew and remove the high voltage lead connector at the spark plug. Exercise care to avoid
fouling or damaging the connector.
C. Remove the grommet.
D. Using a 7/8 inch deep hex socket, unscrew and remove the spark plug. Make sure the spark plug
gasket is removed with the spark plug. It will normally stick on the spark plug threads, but if gasket
should drop into the ventilating air passages of the heater, remove with a wire hook.
2. Inspection and Servicing (Spark Plug):
A.If the spark plug appears to be in good condition, except for a mild coating of oxide on the porcelain
and electrodes, it may be cleaned and reused. Cleaning is accomplished on a conventional airplane type
spark plug cleaner, except that it will be necessary to use two or more adapters in order to raise the long
extension of the plug far enough out of the cleaner nozzle opening to perform an effective job. Plug the
ceramic insert cavity at the terminal end of the plug with a piece of paper or cloth to keep out any of the
cleaning sand. Wipe this cavity out thoroughly with a cloth wet with carbon tetrachloride. If after
cleaning the spark plug porcelain is white and the electrodes are not eroded, proceed to check the ground
electrode in the heater and adjust the spark gap in accordance with Step 3 of this paragraph.
— Note —
If the spark plug fails to clean up properly and/or if the electrodes are badly eroded, it
should be replaced.
3. Spark Gap Check and Adjustment: (See Figure 21-12.) A spark gap of 0.156 to 0.188 inches must be
maintained on the P/N 39D18 spark plug. This gap should be checked any time a plug is replaced or at
the time of heater overhaul. A spark gap greater than that specified can shorten the life of the ignition
assembly. There are several methods in which the spark gap of this heater may be checked. Method I is
recommended when the heater is being overhauled and before the installation of the fuel nozzle. Methods
II and III are suitable for checking the gap through the spark plug well when the heater is not
disassembled.
Method I.
A. Using a 5/32 inch drill (0.156) or a piece of 5/32 rod, reach through the small opening in the
combustion head and find the ground electrode. (It is welded inside the head.)
B. 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 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.
C. Recheck the gap after repositioning of the ground electrode.
Method II.
A. Measure the distance between the seating surface of the spark plug with a new gasket installed to
the end of the plug electrode.
B. Using a depth gauge, measure the distance between the ground electrode in the heater to the spark
plug seating surface in the heater jacket and check this measurement against the measurement
obtained in Step A. The difference should be between 0.156 to 0.188 of an inch.
C. The ground electrode can be bent to obtain the required gap.
PA - 4 4 - 1 8 0 / 1 8 0 T
AIRPLANE MAINTENANCE MANUAL
2 1 - 4 3 - 1 2
Page 21-23
Revised: May 15, 1989
1F14
PIPER AIRCRAFT