What causes frequent cylinder head cracking in Chaochai NGD engines?

[DiJade]

Most cases result from thermal stress caused by cylinder heads operating under abnormally high temperatures. Here are relevant explanations: 1. Temperature: The allowable temperature for gray cast iron cylinder heads is generally below 350°C for standard grades and above 375°C for low-alloy grades. When temperatures exceed the casting's critical threshold, the material's creep strength decreases, causing plastic deformation - the primary source of residual tensile stress. The presence of residual tensile stress is the root cause of thermal fatigue cracks in cylinder heads. 2. Full-load operation: During full-load engine operation, the cylinder head bridge area adjacent to the combustion chamber reaches extremely high temperatures, causing metal expansion. However, this expansion is constrained by surrounding fastening screws, thereby generating compressive stress.