Mitsubishi S4S Service Manual page 141

1.2 Inspeetion
(1) Armature
(a) Testing for short circuit
Place the armature on a growler, and slowly
revolve it with a hacksaw blade held above
the armature core. The hacksaw blade vibrates
against the core when it is above a slot
containing a shorted winding. Replace the
armature if shorted.
(b) Testing for grounded circuit
If there is any continuity between the
commutator and shaft (or core), the armature
is grounded and should be replaced.
(c) Measuring commutator runout
1) Support the armature in V-blocks and
measure the runout of the commutator with
a dial indicator. If the runout is near the
service limit, recondition the commutator,
making sure the commutator diameter does
not exceed the service limit. If the
commutator surface is rough smoothen it
with a sandpaper of #300 to #500.
Unit: mm [in.]
Item
Assembly Service
Standard Limit
Runout of commutator
0.03 0.1
[0.004] [0.0012]
ELECTRICAL SYSTEM
Testing for short circuit
Testing for grounded circuit
Measuring commutator runout
12-3