What was found
DURING CLIMB, THE PILOT REPORTED CHT ON THE NR 2 ENG WAS 450° & CLIMBING. HE EXECUTED A PRECAUTIONARY LANDING AT THE DEPARTURE AIRPORT. THE NR 6 CYLINDER, WHERE THE CHT PROBE IS LOCATED, WAS FOUND TO HAVE A CRACK FROM THE UPPER SPARK PLUG HOLE TO THE INTAKE VLV. THE NR 6 CYLINDER WAS REPLACED WITH NEW, & ALL OTHER CYLINDERS ON THE ENG WERE INSPECTED RESULTING IN FINDING 2 OTHER CYLINDERS THAT APPEARED TO HAVE CRACK INITIATION. THE CRACKS START BETWEEN THE 14TH & 15TH COOLING FINS ON THE TOP OF THE INTAKE PORT SIDE OF THE CYLINDER. THE FIRST EVIDENCE OF A PROBLEM IS BLUE FUEL STAINING IN THIS AREA, WHICH WE INITIALLY MISTOOK FOR A LEAKING INTAKE GASKET. SERVICE INSTRUCTION 1553 ADDRESSES THIS PROBLEM, BOTH BY ADVISING TECHNICIANS TO LOOK FOR CRACKING IN THE AREA & TO PREVENT THE PROBLEM FROM OCCURRING BY INSTALLING A FIN STABILIZER. HOWEVER, THOUGH THAT BULLETIN WAS RELEASED OVER 2 YEARS AGO, MFG DOES NOT SHIP SPARE CYLINDERS WITH THE STABILIZER INSTALLED. ALSO, HISTORICALLY THIS IS NOT A COMMON ISSUE. THE DAMAGED CYLINDERS HAVE BEEN SENT TO MFG & OUR INVESTIGATION IS ONGOING.