G424 Service Manual Starting System41
6EN0874
Free Running Test
(1) Place starter motor in a vise equipped with soft jaws and
connect a fully-charged 12-volt battery to starter motor as
follows:
(2) Connect a ammeter (100-ampere scale) and carbon pile
rheostat in series with battery positive post and starter
motor terminal.
(3) Connect a voltmeter (15-volt scale) across starter motor.
(4) Rotate carbon pile to full-resistance position.
(5) Connect battery cable from battery negative post to
starter motor body.
(6) Adjust the rheostat until the battery voltage shown by the
voltmeter is 11V.
(7) Confirm that the maximum amperage is within the
specifications and that the starter motor turns smoothly
and freely.
Current: max. 60 amps
Symptom Possible cause
Current is too large, and starter motor •Contaminated or oil stained metal
rotates at too low speeds. •Friction between armature core and pole piece
( Motor output torque is insufficient.) •Armature coil and/or field coil not properly grounded
•Armature coil short-circuited
Current is too large, and motor does •Electromagnetic switch not properly grounded
not rotate at all. •Armature coil and/or field coil not properly grounded
•Seizure of metal
No current is available, and motor •Armature coil and/or field coil open-circuited
does not rotate. •Brush and/or pigtail open-circuited
•Poor contact of brush and commutator due to contaminated
commutator, high mica, etc.
Current is too small, and motor rotates Loose field coil connections (If the shunt coil alone is
at low speed. (Motor output torque is open-circuited or loosely connected, the motor will
insufficient.) rotate at a high speed.)
Current is too large, and motor rotates at Field coil short-circuited
too high speeds. (Motor output torque is
insufficient.)
Variable resistance
Ammeter
Voltmeter
Starter
motor
M
Battery
12
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