Bending or breaking due to problems with the connecting rod itself. This situation can generally be determined by chemical composition analysis and hardness test of the connecting rod material, metallographic structure test, scanning electron microscope fracture analysis and other methods.

Low stress fatigue fracture is caused by quenching microcracks, and pearlite + flake, oversized non-metallic inclusions, blocky ferrite, etc. in the organization cause the mechanical properties and fatigue life of the connecting rod to decrease.

Improper maintenance operation leads to bending or breaking of the connecting rod. For example, there is no cleaning fluid during the carbon deposit cleaning process in the immersion method, which causes the Bare Engine to top the cylinder when restarting.

For Cummins Engine equipped with a variable intake system, if the cleaning agent flow rate does not match the speed of the Bare Engine.

If the intake system is not disassembled for cleaning, it may cause excessive cleaning agent to accumulate in the intake manifold. When driving at high speed, the cleaning agent in the intake manifold will be instantly sucked into the combustion chamber, causing the top cylinder.