As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT CRUISE POWER SETTING, CREW REPORTED A ROUGH RUNNING RT ENGINE ALONG WITH A CONTINUOUS MODERATE VIBRATION THROUGHOUT RANGE OF POWER SETTINGS. THE FLIGHT DIVERTED AND LANDED SAFELY. INSPECTION REVEALED THE NR 6 CYLINDER AND PISTON ASSEMBLY WERE SEVERELY DAMAGED. THE INTAKE AND EXHAUST VALVES DID NOT EXHIBIT SIGNS OF DAMAGE. THE DAMAGE APPEARS TO HAVE BEEN CAUSED BY A PREIGNITION EVENT IN THE NR 6 CYLINDER. THIS ENGINE HAS BEEN REMOVED FROM SERVICE DUE TO METAL CONTAMINATION CAUSED BY THIS EVENT.