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 reports highlight various failures of engine-related drive shafts and gears across different aircraft systems (e.g., pressure pumps, turbochargers, alternators, magnetos, starters, prop governors).
These failures, including shearing, breaking, and wear, occurred in some cases at relatively low part total times, leading to critical operational issues such as loss of power, instrument pressure, or failed engine starts.
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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