Piper SEMINOLE PA-44-180, Maintenance Manual

Page: 132 / 881

Figure 21-10. Spark Plug Fixture Figure 21-11. Wiring - Test Setup
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.
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
NOTE: ALL DIMENSIONS ARE IN
INCHES
* - DENOTES SILVER SOLDER
0.3125 DIA. ROD, 0.50 LONG
1010 - 1020 STEEL ROD
DRILL AND TAP FOR 4-40 SCREW
LOCATE 1/4 IN. EITHER END
SCREW - MACHINE, RD HD.
AN OR MS 4-40 - 1/4 IN. LONG
TYPE II SPARK PLUG
INSTALLED IN FIXTURE
2 HOLES
0.1285 DIA (#30 DRILL)
0.19 DEEP
1.50
0.06
5.00
3.00 INCH
ADJUSTABLE
GAP
0.125 DIA
1010 - 1020
STEEL ROD
1 IN. HEX S.A.E. 1112 SCREW STOCK
0.640 DIA. DRILL CHAMFER 45° X 1/16
NEAR END ONLY
THREAD 18 MM - 1.5 MM PITCH
S.A.E. SPARK PLUG STANDARD
MOMENTARY
SWITCH
EXTERNAL
TEST
CIRCUIT
INTERNAL
TEST
CIRCUIT
BATTERY
AMMETER
VOLTMETER
VIBRATOR
COIL
FILTER
TOTAL RESISTANCE A TO B MUST
NOT EXCEED 0.3 OHMS.
COND.
PA - 4 4 - 1 8 0 / 1 8 0 T
AIRPLANE MAINTENANCE MANUAL
2 1 - 4 3 - 11
Page 21-21
Revised: May 15, 1989
1F12
PIPER AIRCRAFT