If lamp lights. armature is grounded and must be
(3) To test for grounded fields. place one
probe, of test lamp on field frame and other probe on
field terminal. If lamp lights. field coils are grounded and
must be replaced if ground cannot be located and
h. Undercutting Mica. Carefully inspect the
commutator. If burned. rough. or out-of-round, it must
be cut down and the mica undercut.
(1) Place armature in a lathe and turn down
comnmutator until true. Make certain cut is not made on
commutator riser bars as solder will be removed.
weakening coil connections at this section. Remain
approximately 3/ 16 inch from riser bars cutting.
(2) Undercut mica between bars to a depth
not exceeding 0.030 inch. Undercut must be-full width of
mica and flat at bottom. (fig. 3-90.) After undercutting.
clean out slots to remove any dirt or copper dust.
(3) Sand commutator lightly with No. 00
sandpaper to remote an. burrs left from undercutting.
Figure 3-90. Undercutting mica.
(4) Check armature on a growler for short
circuits. Refer to subparagraph h. step (1).
i. Armature Shaft Removal.
Note. Pressure to remove or install shaft may exceed
(1) Place the drive end of the shaft in a heavy
duty pipe approximately 2 1 / 4 inches I.D. and at least
18 inches long. (fig. 3-91.) Caution: Make certain the
top end of the pipe makes complete contact with the
core from above shaft, but within a radius of the core
(2) Place a second pipe of 1 1/4 inches I. D.,
1 1/2 inches maximum 0. D and about 4 inches long.
over commutator end against bearing shoulder on
shaft. Apply vertical pressure on pipe (commutator end)
and press shaft from armature.
(1) Inspect all parts for signs of unusual wear,
broken insulation or loose connections. Replace any
damaged or worn parts.
(2) Reassembly of this unit is a reversal of the
(a) To replace shaft. place a 6 inch, 1
1/2 inch I. D 2 1/4 inch 0. D. pipe against commutator
sleeve with assembly vertical. Insert shaft as far as it will
Figure 3-91. Armature shaft pipes.
go. Using a 1 5 / 8 inch I. D. pipe against bearing
shoulder, apply exact vertical pressure until shaft
bottoms correctly against core support.
(b) Bearing retainer with seal must be
assembled on shaft before installing bearing.