As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SEVERE ENGINE ROUGHNESS OCCURRED WHILE IN FLIGHT. AN OFF AIRPORT LANDING WAS MADE WITH NO DAMAGE TO AIRCRAFT AND NO INJURIES. NR 1 CYLINDER FOUND TO HAVE NO COMPRESSION. FOUND THAT PN 17726 VALVE SPRING WASHER HAD FAILED ALLOWING INTAKE VALVE TO DROP INTO CYLINDER NR 1. ENGINE TSMOH 1106. TSO 418.45. UNABLE TO DETERMINE IF PART WAS REPLACED AT MAJOR OVERHAUL OR TOP OVERHAUL.