What are the causes of starter motor spinning without engagement?

[LukasDella]

The causes of starter motor failure include the following points: 1. Malfunction of the solenoid switch. 2. Broken teeth on the drive pinion or severe wear on the flywheel ring gear. 3. Slippage of the one-way clutch. 4. Damage, misalignment of the starter motor shift fork, or detachment of the linkage hook. 5. Issues with the fit between the armature shaft and armature core inside the starter motor. Here is additional information: 1. Common faults of the solenoid switch generally include open circuit, short circuit, or grounding of the pull-in and hold-in coils, as well as burning of the contact disc and contact surfaces. 2. Check for open circuits or grounding in the coils by measuring resistance with an ohmmeter. If the coils are faulty, rewind or replace them. 3. For minor burning of the contact disc and contact surfaces, they can be repaired with a file or sandpaper. Replace the return spring if it is too weak.