What was found
AT 500.0 HOURS TSO, THE ENGINE FAILED IN-FLIGHT. ENGINE TEAR DOWN REVEALED NR 4 CONNECTING ROD HAD FAILED, PUNCHING A HOLE THROUGH THE CRANKCASE. THE TWO CONNECTING ROD BOLTS HAD FAILED ALLOWING THE CONNECTING ROD TO COME LOOSE FROM THE CRANKSHAFT. THE BOLTS WENT TO THE NTSB FOR ANALYSIS. THE ENGINE WAS OVERHAULED NOVEMBER, 1996, LYC SB 240N REQUIRES REPLACEMENT OF THE CONNECTING ROD BOLTS AT OVERHAUL. EXAMINING THE WORK ORDER FROM THE OVERHAUL, IT WAS UNCLEAR IF THOSE BOLTS HAD BEEN REPLACED.