Piper Navajo PA-31 Service Manual page 928

PIPER NAVAJO SERVICE MANUAL
3.
Looking through the brush guide, inspect the commutator, which should be smooth and
medium brown to dark brown in color. Remove all dust from commutator with compressed air. If the
commutator is grooved in the brush track, gouged, scored or shows signs of having burned spots, replace the
complete motor assembly. If the commutator is in good condition, install new motor brushes, and tighten
brush caps into place. Make sure each brush is oriented so that the curved end fits the curvature of the
commutator.
4.
After installing new brushes, it is advisable to run-in the brushes as follows: Connect the
motor to a controlled voltage supply (rheostat in a 28-volt line). Operate the motor at approximately 1/2
its normal speed for the first hour; then gradually increase the speed until it is rotating at approximately
normal speed. Continue the run-in operation for at least two hours to properly seat the brushes before
installing the blower in the airplane.
c. Installation:
1.
Prior to installing the combustion air blower, inspect all parts of the assembly for loose
screws, loose nuts, and poor ground connection on the blower housing. Make sure the blower wheel is tight
on the shaft and properly located in the housing. It should have just enough clearance to rotate at full speed
without binding. Blower performance is based upon this close-tolerance clearance. It is recommended that
correct voltage be applied for this clearance check.
2.
Install the blower inlet adapter in the same orientation as before removal.
3.
Place the combustion air blower assembly in position in the attaching clamp so the air
tubing can be connected, and slide the tubing into position at the point where it was disconnected during
removal. Tighten the motor in the attaching strap.
4.
Secure the air tubing by tightening the clamp or installing the sheet metal attaching screws.
5.
Connect the wire lead to No. 1 terminal on terminal strip.
6.
Check motor operation. By disconnecting the wire at the No. 3 terminal on heater terminal
strip, blower can be operated without fuel flow to the heater.
13-27. SPARK PLUG.
a.
Removal: (Refer to Figure 13-19 or 13-20.)
1.
Remove the necessary access panels to expose the spark plug area of the heater assembly.
NOTE
Insure that heater electrical circuits are de-energized.
2.
Unscrew and remove the high-voltage lead connector at the spark plug. Exercise care to
avoid fouling or damaging the connector.
3.
Remove the grommet (21). (Refer to Figure 13-27, 13-28 or 13-29.)
4.
Using a .875 inch deep hex socket, unscrew and remove the spark plug (5). Make sure the
spark plug gasket is removed with the spark plug. It will normally stick on the spark plug threads, but if
loose, it might drop into the ventilating air passages of the heater. Should this happen, remove the gasket
with a wire hook. Any evidence of arcing in the cavity requires replacement of the plug. Also check the
mating connector or spark plug insert on the lead assembly.
b. Inspection and Servicing:
1.
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 provide 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, re-gap the spark plug by
carefully bending the ground electrode in accordance with Step c of this paragraph.
Reissued: 10/12/79 HEATING AND VENTILATING SYSTEM
5B22