Cylinder pulling is the phenomenon of scratching up and down in the area where the inner surface of the cylinder liner contacts the piston reciprocating motion. Generally, the cylinder pulling phenomenon often occurs during the running-in period after engine overhaul; some also occur during normal operation. . When pulling the cylinder, generally slight trace-like pull marks appear on the inner surface of the cylinder liner, and less serious sheet-like strains appear. Strains are mostly on both sides of the cylinder liner perpendicular to the axis of the piston pin. The damaged parts of the cylinder are mostly the cylinder liner (inner surface), piston (outer surface) and piston ring (outer surface contact surface).
The basic reason for cylinder damage is that there is local dry friction between the cylinder liner and the piston friction ring. As a result, the asperities on the metal surface contact each other. Under the action of high load, the micro-protrusions deform. During mutual movement, a large amount of frictional heat is generated, which makes the micro-protrusions melt and fuse, and then pull apart, forming scratching traces and producing wear debris. Metal wear debris is embedded on the surface of the piston (there is no lubricant to wash them away), causing scratches on the cylinder wall.
There are many factors that affect cylinder pull, and the situation is more complicated. It is mainly related to the engine's work (temperature and load), the cooperation between the piston and the cylinder liner, and the matching materials. However, the running-in condition of the engine during the running-in period is the key to affecting cylinder pulling. The basic factors that cause cylinder pull have the following three aspects.
1. The temperature between the piston and the cylinder liner of the engine is too high
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℃-85℃. If the engine has a large thermal load or its cooling effect is not good, the engine 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, even because the lubricating oil is carbonized or burned at high temperature, causing the piston ring to stick to the cylinder wall. This results in 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 displacement of the piston in the cylinder liner causes eccentric wear. Due to the deformation of the piston, the piston pin hole is offset, the cylinder is skewed, the connecting rod is bent or twisted, the crankshaft is changed, 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 deposit in the combustion chamber is serious, which will all 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 easy to produce dry friction and cause 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 belts, too small fan air volume, and too low water pump displacement, etc., the engine has poor cooling and caused the engine to overheat. 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.
2. The materials of the piston ring, piston and cylinder liner are not properly matched
There are many auto parts production units in China, and the quality of the parts is unstable. The expansion coefficient of the piston of each manufacturer is different, and the surface hardness of the cylinder liner and the piston ring are different. These may cause the phenomenon of cylinder pulling, such as when replacing the piston ring. , It is necessary to leave enough end clearance according to the standard; chrome-plated cylinder liner should not be equipped with chrome-plated piston ring, so as not to cause hard pull of the cylinder.
3. Assembly and process issues
1) The piston pin is assembled too tightly, which may cause the cylinder to be pulled at the axial ends;
2) The piston pin retaining ring comes out, which can cause extremely serious cylinder pulling;
3) Improper handling of the piston ring incision, the ring incision opening is too large, and the edges and corners protrude when filing;
4) Large clearance on the end face of the piston ring;
5) The engine speed rises too fast when the engine is cold starting, or the load is added too fast.
4. Pay attention to the following points in use
1) During the running-in period after the overhaul of the engine, the operating procedures and the regulations on load shedding and deceleration shall be strictly implemented during the running-in period;
2) Maintain the correct ignition time and avoid adjusting the ignition time too early, which may cause sudden explosion and overheating of the engine;
3) Ensure that enough oil meets the original manufacturer's specifications, check the oil pressure frequently, and change the oil according to the regulations of the run-in period;
4) Add enough cooling water and check the amount of cooling water and water temperature frequently.
In short, preventing the cylinder pulling problem is a complicated and meticulous work. First, the key problem of excessive temperature should be grasped. Secondly, the material of the mating parts and the selection of the matching size gap should be ensured by the assembly and commissioning process. In this way, cylinder pulling can be reduced or prevented.