Maintenance-Triggered cascade failure in a marine diesel engine: Fractographic and numerical analysis of connecting rod rupture caused by valve lash deviation

Abstract

Fracture of the connecting rod in marine diesel engines results in catastrophic mechanical failure, immediate loss of propulsion, and extensive internal damage. While fatigue and overload are often cited, the role of maintenance deviation remains underexplored, particularly in the context of failure prevention systems. This study reconstructs a real-world incident of connecting rod rupture in an ISOTTA V1312 engine, directly linked to miscalibrated intake valve lash. A multi-tiered diagnostic approach was used, combining finite element analysis of combustion and inertial loads, dynamic simulation of tappet oscillation under excessive clearance, and scanning electron microscopy of fractured cap bolts. Results demonstrate that abnormal valve lash destabilized tappet motion, triggering a cascading failure sequence involving bracket fracture, piston–valve collision, and progressive valvetrain misalignment. Fractographic analysis confirmed ductile fracture due to impact in the cap bolts, with no evidence of fatigue. This is the first validated reconstruction directly connecting a single maintenance deviation to a multi-stage structural collapse. The findings emphasize the need to integrate empirical failure markers into safety diagnostics such as Failure Mode, Effects, and Criticality Analysis (FMECA). In-cylinder pressure monitoring is further highlighted as a vital tool for early detection of valvetrain dynamics anomalies.