What was found
ENGINE WITH 450.0 TIS AND CYLINDER NR 2 WITH THE SAME TIS, BUT 31.0 HOURS SINCE REMOVAL/REPAIR/REINSTALLATION. DURING CRUISE FLIGHT, ENG BECAME VERY ROUGH WITH LOSS OF POWER. NORMAL LANDING WAS MADE. UPON INSP OF ENG, FOUND NR 2 CYL (COLD). PERFORMED COMPRESSION CHECK, NR 2 CYL HAD NO COMPRESSION. BOROSCOPED CYL AND FOUND CRACK PRESENT IN THE ALUMINUM CYL HEAD APPROX CENTERED ON EXHAUST VALVE SEAT AND EXTENDING IN CIRCULAR PATTERN, 2 PLUS INCHES IN EITHER DIRECTION. AFT END SEEMED TO RELIEVE ITSELF ON EDGE OF LWR SPARK PLUG BOSS (LWR SPARK PLUG HAD NO TORQUE WHAT SO EVER). THERE WAS A HOLE (.25 INCH WIDE X .375 INCH LONG) ON FWD END OF CRACK WITH EXHAUST GASES/DEPOSITS PRESENT ON CYL COOLING FINS. (K)