As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT THE NR 4-CYLINDER EXHAUST ROCKER ARM HOLD DOWN STUDS BROKE CAUSING THE NR 4-CYLINDER EXHAUST VALVE TO NOT OPEN. THIS CAUSED EXTREME VIBRATION AND A SIGNIFICANT LOSS OF ENGINE POWER. AIRCRAFT WAS WITHIN GLIDING DISTANCE OF RUNWAY AND LANDED SAFELY. THIS IS THE SECOND OCCURRENCE OF THIS ISSUE WE HAVE HAD ON THESE AIRCRAFT IN LESS THAN A YEAR.