Combustion Air Blower Maintenance; Spark Plug Maintenance - Piper Navajo Chieftain PA-31-350 Service Manual

NAVAJO CHIEFTAIN SERVICE MANUAL
13-25. COMBUSTION AIR BLOWER.
a. Removal.
1.
Disconnect wire at quick-disconnect terminal.
2.
Disconnect the inlet tubing from the inlet air adapter.
3.
Loosen the clamps that hold the combustion air blower assembly in the support bracket and
slide the motor out of the bracket.
b. Replacing Motor Brushes. (Refer to Figure 13-18.)
1.
Remove the brush cap at one of the brush locations. Note position of brush inside the guide
and carefully lift the brush and brush spring out of the guide. Be sure to hold the brush so that it can be
reinstalled in precisely the same position if no brush replacement is required.
2.
Inspect the brush for wear. A new brush is .531 inch long. If brushes are worn to a length of
.187 inch, they must be replaced.
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 against the outer housing. 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. I 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.
13-26. SPARK PLUG.
a. Removal. (Refer to Figure 13-17.)
1.
Remove the necessary access panels to expose the spark plug area of the heater assembly.
NOTE
Insure that the 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 (12) from the heater jacket opening.
4.
Using a 7/8 inch deep hex socket, unscrew and remove the spark plug (6). 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 it with a wire hook.
Reissued: 9/23/80
HEATING AND VENTILATING SYSTEM
4B18