1) The thermal load of the engine is too large, which makes the temperature of the whole machine too high. The best thermal state of the engine is to keep the cooling water temperature between 75℃ and 85℃. The temperature will be too high, the expansion and thermal deformation of the piston will be too large; the gap between the cylinder liner and the piston will be too small, and it will be difficult to form a good lubricating oil film. The result is sudden explosion and pre-ignition, resulting in a dry friction state, and aggravating engine wear.
2) The accuracy, smoothness and shape (taper and ovality) of the inner surface of the cylinder liner exceed the specified standards. The sealing effect of the piston ring is reduced, and the combustion gas in the cylinder rushes into the piston skirt, which causes the skirt to become too hot, deteriorate the lubrication, and cause local dry friction.
3) The installation position of the piston in the cylinder liner is offset and the eccentric wear occurs. Due to the deformation of the piston, the piston pin hole is offset, the cylinder is skewed, the connecting rod is warped or twisted, the crankshaft changes axis, and the crank pin and the main journal are not parallel. For other reasons, the piston will be unilaterally biased in the cylinder. At this time, the pressure of the piston ring on the cylinder wall is relatively concentrated on the local surface, so that the oil film between the cylinder liner and the piston ring becomes thin under high pressure, or even ruptured, thereby losing the lubrication effect and forming dry friction And the temperature increased sharply.
4) Engine deflagration. When the engine is working, the fuel octane number is too low, the ignition time is too early, the compression ratio is too high, the spark plug is overheated, and the carbon deposits in the combustion chamber are serious, all of which will cause deflagration. As a result, the local temperature of the cylinder wall is rapidly increased, the lubricating oil film is destroyed or coked into viscose, and the piston ring is stuck in the ring groove, causing air leakage. In addition, the combustion gas is knocked against the cylinder wall caused by deflagration, which makes the cylinder liner prone to dry friction and scratches.
5) Poor lubrication of the inner surface of the cylinder liner. Due to insufficient lubricating oil, low oil pressure, poor oil quality and other factors, it is impossible to ensure that the heat generated by the metal friction surface is taken away during lubrication, which will cause high-temperature deformation of the metal.
6) Poor cooling effect. Due to the lack of water, the internal blockage of the radiator, the outer wall of the cylinder liner and excessive scale, improper installation of the fan, too loose fan belt, too small fan air volume, too low water pump displacement and other factors, the engine is not cold and the engine is overheated. Disadvantages such as high water temperature and lubricating oil temperature. In particular, overheating occurs during the running-in period, and cylinder pulling is prone to occur.
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