Cylinder pulling refers to the phenomenon of scratches and scratches occurring in the area where the inner surface of the cylinder liner contacts the reciprocating motion of the piston. Generally, cylinder pulling often occurs during the running in period after engine overhaul; Some also occur during normal operation. When pulling a cylinder, there are generally mild ripple like pulling marks on the inner surface of the cylinder liner, and there are fewer severe patch like pulling injuries. The areas of strain are mostly on both sides of the cylinder liner surface perpendicular to the piston pin axis. The damaged components of cylinder pulling are mostly cylinder liners (inner surface), pistons (outer surface), and piston rings (outer contact surface).
The basic reason for cylinder damage is local dry friction between the cylinder liner and the piston friction ring. As a result, the micro convex bodies on the metal surface come into contact with each other. Under high load, the micro convex body deforms, and during mutual motion, a large amount of frictional heat is generated, causing the micro convex body to melt and fuse, and then open, forming scratch marks and generating wear debris. Metal debris is embedded on the surface of the piston (without lubricating oil washing them away), causing scratches on the cylinder wall.
There are many factors that affect cylinder pulling, and the situation is also quite complex. It is mainly closely related to the operation of the engine (temperature and load), the fit between the piston and cylinder liner, and the matching materials. However, the running in condition of the engine during the running in period is the key factor affecting cylinder pulling. There are three basic factors that cause cylinder pulling.
1. The temperature between the piston and cylinder liner of the engine is too high
1) The thermal load of the engine is too high, causing the overall temperature to be too high. The optimal thermal state of the engine is to maintain the cooling water temperature between 75 ℃ and 85 ℃. If the thermal load of the engine is too high or its cooling effect is poor, the engine temperature will be too high, and the piston expansion and thermal deformation will be too large; The clearance between the cylinder liner and the piston is too small, making it difficult to form a good lubricating oil film between them. Even, due to the carbonization or burning of the lubricating oil at high temperatures, the piston ring adheres to the cylinder wall, causing sudden explosion and early ignition, resulting in a dry friction state and exacerbating engine wear.
2) The accuracy, smoothness, and shape (taper and ellipticity) of the inner surface of the cylinder liner exceed the specified standards. The sealing effect of the piston ring is reduced, and combustion gas in the cylinder flows into the piston skirt, causing the skirt temperature to be too high and the lubrication situation to deteriorate, resulting in local dry friction.
3) The installation position of the piston in the cylinder liner is offset, resulting in eccentric wear. Due to deformation of the piston, offset of the piston pin hole, misalignment of the cylinder lining, bending or twisting of the connecting rod, change of the crankshaft shaft, and non parallelism between the crank pin and the main journal, the piston can lean on one side in the cylinder. At this point, the pressure of the piston ring on the cylinder wall is relatively concentrated on the local surface, causing the oil film between the cylinder liner and the piston ring to become thin or even rupture under high pressure. As a result, the lubrication effect is lost, forming dry friction and a sharp increase in temperature.
4) Engine detonation can occur when 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 carbon deposits in the combustion chamber are severe during engine operation. The result is a rapid increase in the local temperature of the cylinder wall, causing damage to the lubricating oil film or coking into a viscous colloid, which sticks the piston ring in the ring groove and causes air leakage. In addition, the combustion gas caused by detonation strikes the cylinder wall, making the cylinder liner prone to dry friction and scratches.
5) Poor lubrication on the inner surface of the cylinder. Due to factors such as insufficient lubricating oil, low oil pressure, and poor oil quality, it cannot be guaranteed that the heat generated by the metal friction surface will be carried away during lubrication, resulting in high-temperature deformation of the metal.
2. Improper material matching of piston rings, pistons, and cylinder liners
There are many units producing engine parts in our country, and the quality of the parts is unstable. The piston expansion coefficient of each manufacturer is different, and the surface hardness of the cylinder liner and piston ring is also different. These may cause cylinder pulling. When replacing the piston ring, sufficient end clearance should be left according to the standard; Do not install chrome plated piston rings on the chrome plated cylinder liner to avoid causing hard cylinder pulling.
3. Assembly and process issues
1) The piston pin assembly is too tight, which can easily cause cylinder pulling at both ends of the axial direction;
2) The detachment of the piston pin retaining ring can cause extremely serious cylinder pulling;
3) Improper handling of the piston ring incision, the incision opening of the ring is too large, and the edges and corners protrude when filing the mouth;
4) Large end face clearance of piston ring;
5) When the engine starts cold, the speed increases too quickly or the load is added too quickly.
In short, preventing the problem of cylinder pulling is a complex and meticulous task. Firstly, the key issue of high temperature should be grasped, followed by the selection of the material and size gap of the mating parts, and finally ensured by the assembly and testing process. Only in this way can the phenomenon of cylinder pulling be reduced or avoided.
