As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE DOING COMRPESSION CHECK ON THE ENGINE, FOUND LOW COMPRESSION NR 5 CYLINDER. REMOVED ROCKER BOX COVER AND FOUND THE EXHAUST VALVE TOP STEM WORN DOWN TO BE EVEN WITH THE ROTATOR. THE ROCKER ARM WAS ALSO DAMAGED BY HITTING THE ROTATOR. VALVE MAY HAVE BEEN DEFECTIVE.