COMBUSTION AIR BLOWER.
1. Removal:
A. Disconnect wire at quick disconnect terminal.
B. Disconnect the inlet tubing from the inlet air adapter.
C. Loosen the clamps that hold the combustion air blower assembly in the support bracket and slide the motor out of the bracket.
2. Replacing Motor Brushes: (Refer to Figure 21-19.)
A. 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.
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B. Inspect the brush for wear. If brushes are worn to a length of .187 of an inch, they must be replaced.
C. 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.
D. 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 14 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 aircraft.
3. Installation:
A. 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 inlet housing. Blower performance is based upon this close tolerance clearance. It is recommended that correct voltage be applied for this clearance check.
B. Install the blower inlet adapter in the same orientation as before removal.
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C. 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. Do not tighten until after tightening the motor in the attaching strap.
D. Tighten the blower motor mounting strap securely making certain the air tubing is in proper alignment.
E. Secure the air tubing by tightening the clamp or installing the sheet metal attaching screws.
F. Connect the wire lead at the quick-disconnect terminal.
G. Connect the ground lead securely to the mounting bracket.
H. 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.
SPARK PLUG.
1. Removal: (Refer to Figure 21-18.)
A. Remove the screws in the nose and lower the nose cone gaining access to the spark plug area of the heater assembly.
— Note —
Insure that heater electrical circuits are de-energized.
B. Unscrew and remove the high voltage lead connector at the spark plug. Exercise care to avoid fouling or damaging the connector.
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