Engine cylinder pulling refers to the failure that the inner wall of the cylinder has obvious longitudinal mechanical scratches and scratches within the movement range of the piston ring. In serious cases, fusible wear occurs, causing difficulty in starting the engine or self flameout. Cylinder pulling is one of the most important engine faults.
The fundamental reason for cylinder pulling is that it is difficult to form oil film between the inner wall of the cylinder and the piston ring and piston, resulting in poor lubrication and even dry friction. There are many specific reasons for this situation. Master Du summarized that there are three aspects:
Reasons for piston set
1. piston ring clearance is too small. If the opening clearance, side clearance or back clearance of the piston ring is too small, the piston ring will be stuck by thermal expansion during engine operation, and will be pressed tightly against the cylinder wall, or the piston ring will be broken, and it is easy to pull out the groove on the cylinder wall.
2. the piston pin is out. As the piston pin circlip is not installed or falls off or is broken, the piston pin is blown out during movement, which is easy to damage the inner wall of the cylinder, causing the cylinder to blow into the crankcase.
3. the cylinder clearance of the piston is too small or too large. If the material of the piston is poor, the manufacturing dimension error is too large, or the piston is deformed after assembling the piston pin, resulting in too small fit clearance between the piston and the cylinder, the piston will be stuck after thermal expansion, and then the cylinder wall will be damaged.
4. the piston ring has serious carbon deposition. Excessive carbon deposition causes the piston ring to stick or bite in the ring groove. At the same time, carbon deposition is a kind of hard abrasive, which will be ground into longitudinal grooves on the cylinder wall.
5. the piston is seriously eccentric. Due to the bending and distortion of the connecting rod, the parallelism and coaxiality deviation of the connecting rod journal, main journal and piston pin seat is too large, causing the piston to deviate from the cylinder obviously, which will accelerate the wear of the piston ring, piston and cylinder wall and destroy the formation of oil film.
Causes of cylinder liner
1. the roundness and cylindricity tolerances of the cylinder liner exceed the allowable range, which greatly reduces the sealing between the piston and the cylinder liner, and the high-temperature gas in the cylinder moves downward, damaging the oil film between the piston and the cylinder wall, thus causing cylinder pulling.
2. the cylinder liner is deformed during assembly. For example, the upper end face of the cylinder liner protrudes too much, and the cylinder liner is deformed after installing the cylinder head; The water stop ring of cylinder liner is too thick, which will cause cylinder liner deformation after being pressed into the engine body, and it is easy to cause cylinder pulling.
Reasons for use
1. whether the cylinder liner size used during assembly does not match the cylinder block and piston.
2. the air filter is not sealed, making the filtering effect worse. Dust, sand and other impurities in the air are sucked into the cylinder, forming abrasive wear. The test shows that if a few grams of dust are sucked in every day, the wear of the cylinder liner will increase by more than 10 times.
3. poor running in. For new or overhauled engines, there are many micro irregularities on the surface of cylinder liners, pistons, piston rings and other parts, and it is difficult to form lubricating oil film. If it is put into heavy load operation immediately without running in, it is easy to cause cylinder pulling and other accidents.
4. always start at low temperature. When the engine starts at low temperature, the lubricating oil has high viscosity and poor fluidity, so it is difficult to form an effective oil film on the inner wall of the cylinder. According to the test of the research department, when the diesel engine is operating under the cooling water temperature of 30 ℃, the wear amount of cylinder liner and other parts is 5 ~ 7 times that of the normal water temperature.
5. the engine is overheated. When the cooling system is poorly maintained or overloaded, the excessive machine temperature not only reduces the mechanical strength of the parts, but also prevents the formation of the lubricating oil film on the inner wall of the cylinder. After the piston and other parts are heated and expanded, they are easy to get stuck in the cylinder liner. As a result, the piston is often partially melted, and the inner wall of the cylinder liner is damaged, forcing the engine to shut down.
In practice, cylinder drawing is often the result of several factors. For example, if the engine without running in is put into full load operation immediately after cold start, cylinder pulling accident is easy to occur.
