Generac Power Systems 10 kW LP Test 65 Test Starter Motor, Shorted, open or grounded armature

Section 4.4

Diagnostic tests

Part 4

DC control

Test 65 – 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 62 verified that circuit board action is delivering DC voltage to the starter contactor relay (SCR). Test 63 verified the operation of the SCR. Test 64 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.

Figure 10. Starter Motor (V-Twin Engines)

Figure 11. Starter Motor (Single Cylinder Engines)

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.

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 77 “Check and Adjust Valves.”

PINION

Figure 12. Check Pinion Gear Operation (V-Twin)

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