What does cylinder topping mean?

[EliasMarie]

Cylinder topping refers to the situation where excessive connecting rod clearance causes the connecting rod to become too long, leading it to hit the engine cylinder when the engine is running. Reasons for cylinder topping: 1. Broken spring: Intake or exhaust valve spring breaks, causing the valve to fall into the cylinder; possibly due to hard objects falling into the combustion chamber. 2. Overly thick gasket: During an overhaul, the replaced connecting rod bearing is too thick, or the piston geometric dimensions do not meet requirements. 3. Blown head gasket: Frequent head gasket failures damage the cylinder block surface, and excessive repair may cause the piston to extend beyond the cylinder block surface when reaching the top dead center, resulting in cylinder topping. 4. Poor fuel quality: The cause of cylinder topping may be the use of low-quality fuel, which solidifies near the valve stem after the engine is turned off, causing the valve to stick in cold conditions and leading to cylinder topping upon startup.