As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
VALVE GUIDE LOOSENED IN CYLINDER HEAD ALLOWING CYLINDER TO MISFIRE. NOTE: DIFFICULT TO DIAGNOSE. COMPRESSION WAS 55/80 UNTIL SPRING ASSY WAS MOVED. SUBMITTER RECOMMENDS CHECKING SPRING ASSYS FOR SIDE PLAY WHEN VALVE COVERS REMOVED FOR ANY REASON.