As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE/DESCENT, FLIGHT LT ENGINE STARTED RUNNING ROUGH. MULTI-FUNCTION EGT/CHT GAUGE REVEALED THAT NR 1 CYLINDER OPERATING TEMPS DROPPED OFF LINE. MAG CHECK REVEALED NO ALLEVIATION. PILOT ELECTED TO SHUTDOWN ENGINE AND COMPLETE UNEVENTFUL LANDING. POST LANDING INSPECTION FOUND THAT NR 1 CYLINDER EXHAUST VALVE OUTER SPRING BROKEN. REPLACED NR 1 CYLINDER AND FIXED PROBLEM.