Why is it difficult to start the ZL30 loader engine after it automatically shuts off

The ZL30 loader made in Xiamen and the 4125 diesel engine made in Chengdu suddenly shut down automatically and failed to start several times. Upon inspection, it was found that the fuel, electrical circuits and engine oil of the engine were normal, but the water level of the coolant in the radiator dropped. When the flywheel was turned with a screwdriver, the rotational torque of the crankshaft increased. Where did the cooling water that dropped from the water level in the water tank go? We remove the four fuel injectors of the engine. When the start switch is pressed, cooling water is sprayed out from the fuel injector seat holes of the third and fourth cylinders. When the flywheel was turned again with a screwdriver, the crankshaft turned normally. Where does this cooling water come from? After we installed the fuel injector, the engine could work normally again, but after running for a while, it experienced the phenomenon of automatic stalling and difficulty in starting. We removed the four fuel injectors of the engine again and pressed the start switch. As a result, cooling water was sprayed out from the fuel injector holes of the third and fourth cylinders.

Based on this, we analyze the reasons: There might be water leakage at a certain part of the lower part of the third and fourth cylinder heads or the cylinder gasket. The cooling water accumulates at the top of the piston, preventing the piston from moving up and down normally and causing the crankshaft to fail to rotate normally. When the cooling water is sprayed out, the piston can move up and down normally and the crankshaft can rotate normally. However, as the cooling water leaks, the water accumulation on the upper part of the piston increases, and it cannot move up and down normally again, nor can the crankshaft rotate normally. Therefore, it causes the engine to have difficulty starting after automatic shutdown.

After removing the cylinder heads, we found that the cylinder gaskets of the third and fourth cylinders were intact, but there were cracks on the bridge between the intake and exhaust valves of the third and fourth cylinder heads, and the cylinder liners of the third and fourth cylinders were severely scratched. We asked the operator and found out that this ZL30 loader often started first and then added cooling water during operation last winter. After working, it often drained the cooling water first and then turned off the engine, which caused a crack in the nose bridge area between the intake and exhaust valves of the third and fourth cylinder heads, and the cooling water leaked into the top of the piston. Due to the good sealing performance of the piston rings, the mixture of oil and water causes the third and fourth cylinders to fail to operate normally. The cooling water is leaking more and more. The cooling water accumulates at the top of the piston, preventing the piston from passing the top dead center and the crankshaft from rotating normally. This makes it difficult to start the engine after it automatically shuts down. The lubrication conditions on the inner walls of cylinders three and four have declined, causing severe cylinder pulling on the inner walls of the cylinder liners.

We replaced the cylinder heads, cylinder liners and piston rings of the third and fourth cylinders. After the running-in period, the loader resumed normal operation.