As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE PERFORMING GROUND RUNS ON L55-020 THE RT GENERATOR FAILED TO COME ONLINE. A TECH WAS SENT TO INVESTIGATE AND HEARD A HIGH PITCHED GRINDING NOISE COMING FROM THE RT ENGINE. THE ENGINE WAS IMMEDIATELY SHUTDOWN AND THE ACFT WAS HANGERED. THE RT GENERATOR WAS REMOVED. WHEN THE RT GENERATOR WAS REMOVED THE GENERATOR ROTOR SHAFT FWD NUT WAS MISSING AND INTERNAL DAMAGE TO THE GENERATOR WAS EVIDENT.