ABYC Diesel Practice Exam

What might be the cause if the starter spins without turning the engine?

1. The fuel system is flooded

2. The over running bender in the starter drive is defective

3. The battery is fully charged

4. The alternator is functioning well

The correct answer is: The over running bender in the starter drive is defective

When the starter spins without turning the engine, it typically indicates an issue with the starter drive engagement. A defective overrunning clutch in the starter drive is a common cause of this scenario. The overrunning clutch is designed to allow the starter to disengage from the engine after it has started. If this component is malfunctioning, the starter may spin freely without properly engaging the flywheel or flexplate to turn the engine over. In this situation, the starter is attempting to start the engine, but due to the defective overrunning clutch, it is unable to create the necessary connection to transfer torque to the engine. This results in the starter motor spinning without having the desired effect of cranking the engine. Other factors listed may contribute to various starting issues, but they do not explain why the starter would spin without engaging the engine. For instance, flooding in the fuel system would typically lead to starting difficulties or a no-start condition rather than the starter spinning freely. A fully charged battery or a functioning alternator would ensure that the starter has ample power, but that does not relate to the engagement mechanism of the starter itself.