On attempting to start the engine for a post-maintenance ground run, the propeller turned through approximately three blades then stopped. Propeller was difficult to rotate forward or backward. Inspection of the starters Bendix drive shaft revealed cracks in the gear running parallel to the teeth, causing the gear not to properly mesh with the flywheel.
Multiple aircraft models experienced drive shaft failures in critical engine components, including pressure pumps, turbochargers, alternators, magnetos, and starters.
These failures manifested as sheared, broken, worn, or cracked shafts and gears, leading to a loss of essential functions such as instrument pressure, engine power, electrical generation, ignition, or proper engine starting.
Many of the reported component failures occurred at relatively low operating hours, indicating potential premature wear, material fatigue, or assembly issues.
During a VFR instrument training flight, the instructor noted there was no instrument pressure from either engine. Inspection revealed both engine-driven pressure pumps had sheared their drive shafts. Technicians could not find any obvious reason for both shafts to fail.
Part total time: 88.6 hours
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