As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AIRCRAFT WAS FLYING AT 3500AGL. AT APPROXIMATELY 18 MINUTES ENGINE BEGAN RUNNING ROUGH. PILOT CHECKED ALL INSTRUMENT, ALL WAS NORMAL EXCEPT NR 1 CYLINDER CHT WAS LOW, INDICATING FAILURE. AIRCRAFT BEGIN LOSING ALTITUDE AND FORTUNATELY LANDED SAFELY. DURING INVESTIGATION BY AN AME, NR 1 CYLINDER INTAKE VALVE SPRING (INNER) HAD BROKEN IN FOUR PIECES.