3034 Marine Engine Caterpillar

Starting Motor

Illustration 1	g00803638
Starting and charging system

Table 1 shows the maximum acceptable loss of voltage in the circuits. The battery circuit supplies high current to the starting motor.

Voltage drops that are greater than the amounts in Table 1 are caused most often by the following conditions:

• Loose connections

• Corroded connections

• Faulty switch contacts

Procedures For Diagnosis Of The Starting Motor

The procedures for diagnosing the starting motor are intended to help the technician determine if a starting motor needs to be replaced or repaired. The procedures are not intended to cover all possible problems and conditions. The procedures serve only as a guide.

Diagnosis Procedure

If the starting motor does not crank or if the starting motor cranks slowly, perform the following procedure:

1. Measure the voltage of the battery at the battery posts with the multimeter when you are cranking the engine or when you are attempting to crank the engine. Measure the voltage across the battery posts. Do not measure the voltage across the cable post clamps.

2. Battery voltage

   1. Go to Step 3 if the voltage is equal to the voltage that is given in Table 2 or if the voltage is greater than the voltage that is given in Table 2.

   2. The battery voltage is less than the voltage in Table 2.

      Refer to Special Instruction, SEHS7633 in order to test the battery.

      A low charge in a battery can be caused by the following conditions:

      • Deterioration of the battery

      • A shorted starting motor

      • A faulty alternator

      • Loose drive belts

      • Current leakage in another part of the electrical system

3. Measure the current from the positive "+" battery terminal to the starting motor solenoid. Use the 8T-0900 Ammeter. The maximum current that is allowed for no load conditions is given in the Specifications Module, "Electric Starting Motor" topic.

   Note: If the following conditions exist, do not perform the test in Step 3 because the electric starting motor has a problem.

   • The voltage at the battery post is within 2 volts of the lowest value in the applicable temperature range of Table 2.

   • The large starting motor cables get hot.

   The current and the voltages that are specified in the Specifications Module, "Electric Starting Motor" topic are measured at a temperature of 27°C (80°F). When the temperature is below 27°C (80°F), the voltage will be less than the values that are specified. Also, the current through the starting motor will be higher. If the current is too great, a problem exists in the starting motor. Repair the problem or replace the starting motor.

4. Measure the voltage from point "MTR" to the ground connection of starting motor. Use the multimeter when you are cranking or when you are attempting to crank the engine. Refer to illustration 1.

5. Measure the voltage between the starting motor "MTR" to the ground connection of electric starting motor.

   1. The voltage is equal to the voltage that is given in Table 2 or the voltage is greater than the voltage that is given in Table 2.

      The battery and the starting motor cables to the starting motor are within specifications. Go to Step 8.

   2. The starting motor voltage is less than the voltage specified in Table 2.

      The voltage drop between the battery and the starting motor is too great. Go to Step 6.

6. Measure the voltage drops in the cranking circuits with the multimeter. Compare the results with the voltage drops which are allowed in Table 1.

7. Voltage drops in the cranking circuits

   1. The voltage drops are equal to the voltage drops that are given in Table 1 or the voltage drops are less than the voltage drops given in Table 1. Go to Step 8 in order to check the engine.

   2. The voltage drops are greater than the voltage drops that are given in Table 1. The faulty component should be repaired or replaced.

8. Rotate the crankshaft by hand in order to ensure that the crankshaft is not stuck. Check the oil viscosity and any external loads that could affect the engine rotation.

   1. If the crankshaft is stuck or difficult to turn, repair the engine.

   2. If the engine is not difficult to turn, go to Step 9.

9. Attempt to crank the starting motor.

   1. The starting motor cranks slowly.

      Remove the starting motor for repair or replacement.

   2. The starting motor does not crank.

      Check for the blocked engagement of the pinion gear and the flywheel ring gear.

      Note: Blocked engagement and open solenoid contacts will give the same electrical symptoms.