PART 4
ENGINE/DC CONTROL
Page 66
Section 4.5
Diagnostic Tests
TEST 59 – TEST STARTER MOTOR
Conditions Affecting Starter Motor Performance
1. A binding or seizing condition in the starter motor bearings.
2. A shorted, open or grounded armature.
a. Shorted armature (wire insulation worn and wires
touching one another). Will be indicated by low or no
RPM.
b. Open armature (wire broken) will be indicated by low or
no RPM and excessive current draw.
c. Grounded armature (wire insulation worn and wire
touching armature lamination or shaft). Will be indicated
by excessive current draw or no RPM.
3. A defective starter motor switch.
4. Broken, damaged or weak magnets.
5. Starter drive dirty or binding.
Discussion
Test 57 verified that the controller is delivering DC voltage to
the starter contactor (SC). Test 58 verified the operation of the
starter contactor (SC). Another possible cause of an “engine
won’t crank” problem is a failure of the starter motor.
Procedure
The battery should have been checked prior to this test and
should be fully charged.
Set a VOM to measure DC voltage (12 VDC). Connect the meter
positive (+) test lead to the starter contactor stud which has
the small jumper wire connected to the starter. Connect the
common (-) test lead to the starter motor frame.
Set the AUTO-OFF MANUAL Switch to its “MANUAL” position
and observe the meter. Meter should indicate battery voltage,
starter motor should operate and engine should crank.
Results
1. If battery voltage is indicated on the meter but starter
motor did NOT operate, remove and bench test the starter
motor (see following test).
2. If battery voltage was indicated and the starter motor tried
to engage (pinion engaged), but engine did NOT crank,
check for mechanical binding of the engine or rotor.
If engine turns over slightly, go to Test 70 “Check and Adjust
Valves.”
Figure 41. Starter Motor
Checking The Pinion
When the starter motor is activated, the pinion gear should
move and engage the flywheel ring gear. If the pinion does not
move normally, inspect the pinion for binding or sticking.
PINION
Figure 42. Check Pinion Gear Operation
Tools For Starter Performance Test
The following equipment may be used to complete a
performance test of the starter motor:
•A clamp-on ammeter.
•A tachometer capable of reading up to 10,000 rpm.
•A fully charged 12 volt battery.
Measuring Current
To read the current flow, in AMPERES, a clamp-on ammeter
may be used. This type of meter indicates current flow through
a conductor by measuring the strength of the magnetic field
around that conductor.
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