The direction of the front of the piston is generally perpendicular to the axis of the piston pin hole:

1. The engine is overloaded, causing excessive deformation of the piston, causing fatigue cracking on the top surface of the piston.

2. Abnormal operation of the combustion system or excessive engine load will cause the temperature gradient on the top surface of the piston to increase, resulting in thermal cracking on the top surface of the piston.

3. The material of the piston is unqualified, resulting in a decrease in high temperature strength.

4. If the fuel contains elements such as sulfur and vanadium, it will cause high-temperature corrosion and accelerate the development of cracks.