As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING THE REMOVAL OF A CYLINDER, THE TECH WAS TRYING TO REMOVE THE HYDRAULIC LIFTER ASSY WHEN HE FELT SOMETHING ROUGH INSIDE THE CRANKCASE. VISUAL INSPECTION REVEALED THE CYLINDER-FACING END OF THE NR 4 CYLINDER EXHAUST TAPPET WAS IN PIECES. THERE HAD BEEN NO ABNORMAL OIL ANALYSIS READINGS NOR ANY METAL SEEN IN THE OIL FILTER PRECEDING THIS DISCOVERY.