As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IN FLIGHT HEARD A LOUD NOISE FROM THE NR 2 ENGINE. ENGINE CONTINUED TO OPERATE BUT AT A REDUCED POWER OUTPUT. UPON INSPECTION FOUND ONE HALF OF THE EXHAUST VALVE FACE BROKEN OFF REQUIRING REPLACEMENT OF THE PISTON AND CYLINDER ASSEMBLY.