As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED LEFT PROPELLER VIBRATES ABOVE 2500 RPM. MAINTENANCE INSPECTED AND FOUND THE LEFT ENGINE #1 CYLINDER EXHAUST VALVE ERODED AND RECESSED INTO CYLINDER HEAD, AND #4 THE CYLINDER TO HAVE LOW COMPRESSION AND THE #4 CONNECTING ROD BEARING TO HAVE A CRACK. THE CYLINDERS AND CONNECTING ROD WERE REPLACED, WITH NO FURTHER DISCREPANCIES.