TM 55-4920-231-14
(4) Inspect commutator for signs of high
bearing grease Military Specification MIL-G-
mica at commutator segments.
23827 as instructed on the current lubrication
b. Repair. Replace any defective motor or
order.
pump parts, such as a grounded or shorted field
d. Test. Prior to installing the motor and
winding assembly, worn bearings, defective ar-
pump assembly in the chassis, it can be tested
mature or pump shaft. Repair a commutator
as follows:
which has high mica by undercutting as follows:
(1) Arrange the unit in a test setup com-
(1) Using an approved method, carefully
prised of a reservoir, pressure gage, relief valve
undercut the mica between the commutator seg-
(55 psig), vacuum tank, vacuum gage, and nec-
ments to a depth, of 0.005 to 0.010 x 3/64 of
essary piping.
an inch. Be sure the full width of the mica is
(2) Apply 28 vdc power to the motor. In
removed and that a thin sliver of mica is not
repeated tests the pressure gage should rise con-
sistently to approximately 50 psig. Stop the motor
left against one side of the slot.
(2) Remove all burrs and rough edges from
at this point.
slots by beveling gently to a 45 chamfer.
(3) Check the vacuum gage; it should read
approximately -29.5 in Hg.
(3) Polish with a very fine grade of sand-
paper and finish with felt or canvas.
e. Reassembly and Installation. For reassem
c. Lubrication. Prior to reassembly of motor
bly and installation procedures, refer to para-
graph 81.
and pump, lubricate motor shaft bearings using
Section VI. FRONT PANEL ASSEMBLY OVERHAUL
ments is to be accomplished in accordance with
101. GENERAL.
the applicable technical manuals for the part
The GS maintenance personnel are authorized
numbers as listed below:
to overhaul the instruments and tester as speci-
fied in the Maintenance Allocation Chart (Ap-
PART NO.
INSTRUMENT
pendix B). The equipment must be restored to
MS 28049
Rate-of-climb Indicator
a completely serviceable condition as prescribed
MS 28044-1
Altimeter
by serviceability standards developed and pub-
MS 28021-1
Airspeed Indicator
AN 5770-5
lished by heads of technical services. This is ac-
Manifold Pressure Gage
(MS 28077-5)
complished through employment of the tech-
nique of Inspect and Repair Only as Necessary
MS 28061-1
Fuel Pressure Gage
(IROAN). Maximum utilization of diagnostic
and test equipment is combined with minimum
103. TESTER OVERHAUL.
disassembly of the item during the overhaul
Overhaul the instruments as instructed in
process.
tester components in accordance with instructions
in chapter 3.
The removal and installation of the instru-
