Fault Phenomenon: Sumitomo crawler crane during startup, a loud metallic impact sound is heard, and the engine does not crank.

Troubleshooting Process:
– Removed starter motor: drive gear teeth broken.
– Checked flywheel ring gear: ring gear also damaged.
– Replaced starter motor assembly and flywheel ring gear.

Root Cause: The starter motor return spring failed, preventing the gear from retracting in time, causing it to be driven by the flywheel at high speed, resulting in tooth breakage.

Required Parts: Starter motor assembly, flywheel ring gear.