As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING PERFORMANCE OF SB388C AND SB301B. THE NR 6 CYLINDER EXHAUST VALVE OUTER SPRING WAS FOUND BROKEN NEAR THE UPPER SPRING SEAT. NO ENGINE PERFORMANCE ISSUES WERE NOTED PREVIOUSLY AND ALL NRS FROM SB388C WERE WITHIN LIMITS. INNER AND OUTER EXHAUST VALVE SPRINGS WERE REPLACED. ACFT GROUND RUN WAS PERFORMED WITH NO DEFECTS FOUND. ACFT HAS BEEN RELEASED TO SERVICE.