As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RIGHT ENGINE STARTED TO BACKFIRE AND RUN ROUGH. ENGINE WAS SHUT DOWN IN-FLIGHT AND PROP FEATHERED. UPON TROUBLESHOOTING, FOUND VALVES ON REAR CYLINDERS NOT ACTUATING. SUSPECT BROKEN CAM GEAR. ENGINE WAS REMOVED FOR REPAIR AND A SERVICEABLE ENGINE WAS INSTALLED.