How to identify Generator starter motor problems and solutions.

The starter motor provides the power required to start the diesel engine's compression sequence. While the engine is running, it receives a continual recharge from the electrical system. You can also read How does a diesel engine produce electricity?

 What is a starter motor for a generator?

An electric motor that starts the generator is a generator starter motor. Once the generator is operating, an internal combustion engine is a system that depends on the momentum of one cycle to begin the next.

In a four-stroke engine, the third cycle uses energy from the fuel to power the exhaust stroke, the external load, and the first two cycles of the following process, i.e., intake and compression.

Every session's first two strokes must come from a different source than when the engine starts the first cycle. The starter motor serves this purpose, but it is no longer required once the engine runs and its feedback loop is self-sustaining.

You might be wondering why I need coolant and what it does.

How do generator starter motors work?

The engine begins to spin over and crank when you depress the start button or turn the start key. But it takes a lot more work than you may imagine getting it going. The engine can only draw air in by creating suction.

Air won't exist if your engine isn't running. Without air, fuel cannot burn. The starter motor is in charge of starting the engine and igniting it while also enabling the subsequent steps.


When you press the start button, the starter motor activates, turning the engine over so it can breathe. The flywheel at the crankshaft's end of the machine has a ring gear attached to it. The starter's pinion must fit into the ring gear's slots.

The body's internal electromagnet activates when you press the start button, pulling a rod with a pinion attached outward. As the flywheel and pinion make contact, the starter motor rotates. The engine spins, as a result, bringing fuel and air into the combustion chamber.

The starter motor disengages, and the electromagnet ceases as the engine starts. Once more, the rod is drawn back into the starter motor, removing the pinion from contact with the flywheel and shielding it from potential harm.

Components of a starter motor and their purposes 

The following components make up a starter motor;


The commutator is a portion of the housing's shaft where the brushes run to conduct electricity. Two plates fastened to the armature's axle make up the commutator. The coil of the electromagnet has two connections provided by these plates.

Field Coils: 

The field coils, which consist of two or more rings connected in series, are secured in the housing by screws. The battery provides energy to these coils, which are then transformed into an electromagnet and used to rotate the armature.


Two wire coils coiled around a movable core make up the solenoid. The starter motor and the generator's battery have an electrical connection that is opened and closed by this solenoid, which also acts as a switch. 


A pinion is a tiny device with a gear and a spring within. By extending the equipment to the flywheel teeth, it engages as soon as the engine starts. The machine rotates because of the flywheel.


The solenoid and linked generator battery work together to propel the plunger forward, engaging the pinion.

Liver Fork

Because the plunger and the lever fork are connected, the lever fork moves forward together with the plunger, and when you engage, the pinion by this method.


The brushes move along a piece of the commutator located at the back of the housing, coming into contact with its contacts and carrying electricity.


A driving shaft and bearings: are used to support the electromagnet armature. It has a soft iron core that has been laminated and is in a variety of conductors, loops, or windings.

Identify generator starter problems.

There are a few signs that may indicate a problem with the starter of a generator:

The generator won't start: If the generator doesn't start at all, it could be an issue with the starter

  • The generator starts slowly: If the generator takes longer than usual to start, it could be a problem with the starter.
  • The generator makes a clicking sound: If the generator makes a clicking sound when you try to start it, it could be an issue with the starter.
  • The generator makes a grinding sound: If the generator makes a grinding sound when you try to start it, it could be an issue with the starter.
  • The generator smells like burning: If the generator smells like burning when you try to start it, it could be an issue with the starter.

If you suspect that there is a problem with the starter of your generator, it is best to have it checked by a qualified technician. They will be able to diagnose the issue and recommend the appropriate repairs.

 What are the symptoms of a generator starter motor, and how to fix it?

Weak starter motor.


The diesel engine cannot enter the self-operating stage when it first begins because the crankshaft does not turn or rotates slowly. 


(1) Not enough battery power. 

(2)The starting resistance is excessive, or the movable and static contacts of the electromagnetic switch are damaged or burned. (3). Poor contact comes in second. 


1. Verify the battery's level of charge.

2. Verify the brush's contact with the commutator. Replace the meeting if necessary.

3. Look for burnout and scratches on the commutator. Clean the commutator's surface with diesel or gasoline if there is more dirt. Repair or replace it if necessary if there is significant burning, abrasion, and scratching and if the surface is not smooth or round. 

4. Verify the working contact surfaces of the two static contacts and the electromagnetic switch. You can ground the movable contact and the fixed contact with an acceptable abrasive cloth if they are faulty and the starting motor is running weakly.

The starter motor does not rotate.


(1). The magnetic switch makes a sucking sound, but the starter motor does not move.


(1). Insufficient battery power, inadequate start-up line contact, or a problem with the starter motor itself could be the root of the problem.

(2). Starting motor does not revolve, and the magnetic switch does not pull in.

(3). Direct current motor, electromagnet switch, or start switch circuit failure.


1. When starting the diesel engine, check for smoke, unusual heat, and noise at the battery terminals, start line, DC motor brush parts, and electromagnetic switches, among other places. You have checked the component for anomalies.

2. Verify whether the startup insurance is invalid.

3. Verify that the starting line's joint components, such as the battery terminals, electromagnetic switch terminals, and starter switch terminals, are tightly fastened.

4. With a multimeter, check the voltage drop of the battery when starting the diesel engine. The battery is insufficient if the voltage measured before the start is less than 12.5V. The battery will not start if the measured voltage is less than 12.5V and the voltage decreases during startup are higher than 1.5V.

5. Check for errors in the startup circuit.

 Short-circuit the battery terminal and the switch terminal of the electromagnetic switch using a screwdriver. 

The start line other than the electromagnetic switch is faulty if the electromagnetic control is closed, and the starter generally operates after a short circuit. If the start key switch, start button, and line connectors are not in good contact. 

If, after the short circuit, the electromagnetic switch is still unconnected, there may be an internal open course in the starter or electromagnetic switch.

6. Shorten the magnetic field terminal and battery terminal with a screwdriver. If the starter motor runs without any issues, the electromagnetic switch is probably the source of the issue.

It would be best to examine the burning contact within the electromagnetic switch and the burning state of the two static connections. If the magnetic coil is faulty, remove it from the starter motor.

If a spark appears, there is likely a short circuit inside the starter motor, which needs to be fixed or replaced. Know about the Automatic transfer switch here.

How To Replace A Starter motor in a diesel engine generator (Step-By-Step Guide)

Replacing a starter motor in a diesel engine generator typically requires a few tools and some mechanical knowledge. Here is a general step-by-step guide to help you with the process:

1. Disconnect the battery cables from the generator. It is essential to ensure that there is no electrical power flowing to the starter motor while you are working on it.

2. Locate the starter motor. It is typically located near the front of the engine and is attached to the engine block with bolts.

3. Using a wrench or socket set, remove the bolts that hold the starter motor in place. Some starter motors may also be attached to the engine with a mounting bracket, in which case you will need to remove the bracket.

4. Carefully pull the starter motor away from the engine. You may need to wiggle it a bit to free it from the engine block.

5. Once the starter motor is free, you will need to disconnect the electrical wires that are attached to it. These wires will typically be connected to the starter motor with terminal connectors. Carefully disconnect the wires, taking note of their positions so you can quickly reconnect them later.

6. With the electrical wires disconnected, you can now remove the starter motor from the engine altogether.

7. Take the old starter motor to a parts store and purchase a new one compatible with your diesel engine generator.

8. Install the new starter motor by reversing the steps you used to remove the old one. It means attaching the electrical wires to the terminal connectors and bolting the starter motor to the engine block or mounting bracket.

9. Once the starter motor is securely in place, reconnect the battery cables and test the generator to ensure the starter motor is working correctly.

10. If the generator starts and runs smoothly, you have successfully replaced the starter motor. If it does not start, double-check your work and make sure that all connections are secure and that the starter motor is installed correctly.


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