What was found
WHILE TROUBLESHOOTING A LEAKING INTAKE VALVE GUIDE SEAL, FOUND A CRACK IN THE NR 1 CYL EXHAUST PORT. FOUND SAME CRACKS IN NR 4 AND NR 5 CYLINDERS. YOU CANNOT SEE THEM WITHOUT DROPPING THE EXHAUST STACKS OFF THE ENGINE. THESE CYLINDERS HAD APPROX 850 HOURS SMOH, BUT HAVE BEEN O.H. 2 PREVIOUS TIMES SO THEY MAY HAVE HAD AS MUCH AS 3650 HOURS SINCE NEW. SUGGEST A 500 HOUR INSPECTION ON O.H. CYLINDERS ON TURBOCHARGED 520 ENGINES.