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 TM 55-1905-217-34
due to deterioration of the insulation. This can be checked with a 110 volt test lamp and test points, checking
from the commutator to the armature laminations. If the lamp lights, a ground exists, and the armature must be
replaced.
(b) Open. The armature may become open circuited at the commutator riser bars as a result of long
cranking periods, which overheat the unit and cause the armature leads to become open circuited. An open
circuited armature is often easy to detect, since this condition produces some badly burned commutator bars
with other bars fairly clean. Since the armature is of a welded construction such a condition will be rare, but if it
does occur, replace the armature.
(c) Short. A short circuit may occur between adjacent armature leads due to deterioration of the
insulation. To check an armature for short circuits, place armature on a growler and hold a thin steel strip
lengthwise on the core parallel to the shaft. Slowly rotate the armature through a complete revolution. If a
short circuit is present, the steel strip will become magnetized and vibrate. Inspect the commutator slots
carefully, since copper or brush dust sometimes collects in the slots and shorts adjacent bars. If short circuit
still exists, replace armature.
(2) Field coils.
(a) Ground. The fields may become grounded to the frame due to deterioration of the insulation. This can
be checked with a 110 volt test lamp and test points, checking from the field coil terminals to the frame. If the
lamp lights, a ground exists, and the defective field coil must be replaced.
(b) Open. An open circuited field coil can be checked with a test lamp and test points, checking the two
extremities of each field coil. If the test lamp fails to light, an open circuit exists and the defective field coil
must be replaced.
j. Reassembly of Frame and Field Assembly.
(1) Place washer (3, figure 4-12), and inside flat insulation washer (10) on field terminal stud (5) and
insert into frame (1). (2) In order, place these items onto the field terminal stud (5) : insulated stud
bushing (9) , stud insulator (8) , washer (3) , lockwasher (7) , terminal stud nut (4) , lock washer (7)
and terminal stud nut (6).
(3) Insert two ventilators (11).
(4) Put into place the two pieces of field coil insulation strip (15) and the field coil insulating strip (16).
(5) Position in the frame two field coil assemblies (14 and 17) and four pole shoes (13). Secure with
eight pole shoe screws (12).
(6) Solder the field coil leads onto the field terminal stud (5).
k. Reassembly of Commutator End Bearing Assembly.
(1) Install and ream sleeve bearing (5, fig. 4- 11) per paragraph 4-3h(3) above. Install expansion plug (6)
and lubricating wick. Apply 8 to 10 drops of engine oil OE-10 (Specification MIL- L-2104) to wick.
(2) Attach the brush screw support plate with the brush and stud plate (12) with the three brush plate
attaching screws, lock washers and plain washers.
(3) Install this brush plate assembly into the commutator end bracket (4).
(4) Install the following in the order presented: insulated terminal stud bushing (11) , terminal stud insulator
(10) , flat washer (9) , terminal stud lockwasher (8) , terminal stud nut (7) , terminal stud lockwasher (8) and
terminal stud nut (7).
(5) Two brush holders may be installed as follows:
(a) Place the brush holders (16) and brush holder spacer plates onto the brush and stud plate (12).
(b) Insert the brush springs (18), brush holder pins (17) and the lockwashers and brush holder screws
(3). (6) The other two brush holders may be installed as follows:
(a) Place the brush holders (16) and brush holder spacer plates onto the brush and stud plate (12).
(b) Insert the brush springs (18) , brush holder pins (17) and the lockwashers (2) and brush holder
screws
l. Reassembly of Middle Bearing Assembly.
(1) Install new sleeve bearing (5, fig. 4-10) into bracket (3) per paragraph 4-3h(3) above.
(2) Press a new seal (6) into the bearing bracket.
(3) Install pipe plug (4) , lubricating wick (2) and oil hole plug (1). Apply 8 to 10 drops of engine
oil OE-10 (Specifications MIL-L-2104) to wick.
m. Reassembly of Drive Housing Assembly.
(1) Install new sleeve bearing (1, fig. 4-9) in drive housing (4) per paragraph 4-3h(3) above.
(2) Install the drive end lubricating wick (2) , place 8 to 10 drops of engine oil OE-10
(Specification MIL-L-2104) in the reservoir and secure the passage with the pipe plug (3).
n. Reassembly of Starting Motor.
NOTE
Apply light coat of engine oil OE-10
(Specification MIL-L-2104) to inside of all
sleeve bearings prior to final assembly.
4-21
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