The craking direction of piston top is generally vertical to the axial direction of piston oin hole.
The overload run of engine cause the over deformation of piston and relative components and result in the craking of piston top.
The abnormal operation of combustion system or overload of engine cause increased the thermal gradient of piston top and result in thermal craking of piston top.
The inferior of piston materials cause the decreasing of high temperature strength.
If the combustion contains sulfue,vanadium and other element ,it may give rise to high-temperature corrosion and accelerate the seriousness of craking .