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Do You really Know What is Cylinder Pulling in Diesel Generator?

Do You really Know What is Cylinder Pulling in Diesel Generator?

For diesel generators, most user or engineer will talk about cylinder pulling sometimes. But do they all understand what is cylinder pulling? What is cylinder pulling in diesel genearotrs? What situation can be set as cylinder pulling? What is the reason why we will meet cylinder pulling? How to solve this kind of problem?
What is cylinder pulling?
Cylinder pulling is a professional term for engine maintenance. Engine pulling cylinder refers to the obvious longitudinal mechanical scratches and scratches on the inner wall of the cylinder within the movement range of the piston ring. In severe cases, fusion wear occurs, causing difficulty in starting the engine or stalling by itself. failure. Generally refers to the abnormal adhesion and melting marks of the cylinder wall, piston and piston ring, which is a general term for cylinder failure.
Pull cylinder is a major failure of the engine. The root cause of cylinder pulling is that it is difficult to form an oil film between the inner wall of the cylinder and the piston ring and piston, which results in poor lubrication and even dry friction.
The so-called “cylinder pulling” means that the inner wall of the cylinder is drawn into deep grooves, and the friction pair of the piston, piston ring and the cylinder wall loses the sealing property, which leads to the reduction of the compression pressure of the cylinder and the loss of power; the combustible mixture moves down to make the crankcase The increase in pressure will cause the crankcase to explode in severe cases; the lubricating oil will run up into the cylinder and cause the oil burning phenomenon; the exhaust pipe will emit serious smoke; the engine noise will be abnormal; the engine will not work normally or even stall.
Cylinder pulling refers to the phenomenon that the engine piston or piston ring pulls the working surface of the cylinder into scars, causing the piston, piston ring and cylinder wall friction pair to lose sealing.
What situation can be set as pulling situation?
Fristly, the compression pressure of the cylinder is reduced and the power is lost. Secondly, the downward flammable mixture will increase the pressure of the crankcase, which may cause the crankcase to explode in severe cases. Thirdly, the lubricating oil escaping into the cylinder causes the phenomenon of oil burning.Fourthly, the exhaust pipe emits serious smoke; the engine noise is abnormal; the engine cannot work normally or even stalls.
What causes the cylinder pulling?
The main reasons for cylinder pulling are as follows:
The clearance between the piston and the cylinder is too small. The matching clearance between the piston and the cylinder should be strictly in accordance with the requirements of the diesel engine instruction manual. If the clearance is too large, it will be difficult for the diesel engine to start cold. When the engine is cold, the cylinder will knock and the power will decrease. If the clearance is too small, it will cause failures such as pulling and expanding the cylinder. Especially when the linear expansion coefficient of the aluminum alloy used in the piston is relatively large, the above situation is more likely to occur. When repairing diesel engines, if there is no instruction manual for the engine, refer to the fit clearance of similar models. The fitting clearance of air-cooled diesel engines is generally slightly larger than that of water-cooled engines. Generally, for a four-stroke water-cooled diesel engine with a cylinder diameter of 100mm, when aluminum pistons are used, the fit clearance is 0.120 to 0.150mm.
The gap of the piston ring opening is too small. Piston ring opening clearance and backlash are too small, the friction between the ring and the cylinder wall is too large, the carbon deposit in the cylinder is serious, and the dirt or the oil is not clean during assembly, which may cause strain. Piston ring opening gap is too small, the first air ring hits the cylinder sleeve shoulder after the old cylinder is replaced with a new ring, or the piston ring opening expands too large during assembly, which may cause breakage. If the backlash is too small, no special tools are used when disassembling, causing the ring to appear spiral, resulting in elastic effects or serious carbon deposits in the cylinder, which will cause the piston ring to seize. Excessively large opening gaps and side gaps of the piston ring, reverse installation of twisted rings and tapered rings, and clogging of oil passage holes due to excessively dirty lubricating oil can easily lead to oil blow-by. If the piston ring gap is too small, impact at the opening; if the side gap is too large, the ring collides with the land; the old cylinder is replaced with a new ring, and the first gas ring collides with the cylinder sleeve shoulder. These conditions will all cause noise.
Piston ring is broken. The piston is too skewed in the cylinder, resulting in ellipse and taper, and steps appear on the upper part of the cylinder liner. The working surface of the inner wall of the cylinder liner often forms uneven wear and exceeds the limit in the piston ring movement area, generally forming a cone in the reciprocating direction It is ground into an irregular ellipse in the circumferential direction. The ellipticity is often the largest at the position where the cylinder liner wears the most. The non-contact part of the cylinder liner and the piston ring is not worn, so obvious wear steps appear. The stroke gas pressure forces the piston to move to the bottom dead center, from reciprocation to rotation. The pressure of the piston ring on the cylinder liner is the largest in the direction of the crank motion plane, causing eccentric wear of the cylinder liner, that is, the wear of the cylinder liner perpendicular to the crankshaft is the largest. Bending, connecting rod bending, cylinder liner center line and crankshaft axis center line are not perpendicular, crankshaft axial clearance is too large, can cause the piston ring and cylinder liner to produce eccentric wear and uneven force and break. If the bearing gap is too large, the gap between the piston pin and the connecting rod copper sleeve is too large, and there are obvious wear steps on the upper part of the cylinder liner, the first gas ring is most likely to be broken. It is stuck on the piston, or the piston pin circlip is broken or falls off.
The piston and piston ring fall to one side, pressing against the cylinder wall. Due to the deformation of the piston, the deviation of the piston hole, the skewed cylinder, the bending or twisting of the connecting rod, the imbalance between the crank pin and the main journal, the pressure of the piston on the cylinder wall is relatively concentrated, and the local surface makes the cylinder wall and the piston ring The oil film in between becomes thin or even ruptured under great pressure, thereby losing its lubricating effect, forming dry friction and causing cylinder pulling.
The fuel injector (carburetor) has poor atomization for a long time. Automobile fuel injectors are the most sophisticated parts in automobiles. The engine mainly burns gasoline when it is working. During the combustion process, due to the high temperature, the surface or pores of the fuel injector will have carbon deposits and at the same time more colloid will deposit on the inner wall of the fuel injector and the surface of the needle valve during long-term use, which will affect the fuel injection effect and make the injector Clogging, adhesion, causing fuel injection leakage, poor atomization, or even no fuel injection, resulting in increased fuel consumption, decreased engine power, unstable idle speed, poor acceleration, and difficulty in cold starting. The test data indicates that when 10% of the fuel injection volume is blocked, it will lead to incomplete engine combustion, performance degradation, increased fuel consumption, and elevated exhaust temperature. At this time, the fuel injection nozzle should be cleaned in time to improve the combustion efficiency of the engine.
Piston cooling nozzle port failure. The cold cooling of individual engines relies on connecting rod bearings leading to the piston pin and piston nozzles to spray engine oil. Due to various reasons, the oil can not be injected normally, causing the top of the piston to overheat, causing the top of the piston to melt and pull the cylinder. (The role of oil: cooling, lubricating, cleaning, sealing, (rust prevention)
The engine has poor cooling and is running too cold. Engine running at water temperature below 65°C is called cold running. If the engine has not been fully operated and the water temperature reaches a certain level, it will start to work, or when the thermostat is turned on and the temperature is too low, the cooling water enters the large cycle prematurely, which will cause supercooling. When the cylinder wall temperature drops from 800°C to 500°C, the wear of the cylinder liner increases by about 5 times. When the cylinder wall temperature reaches 80°~850°C, the wear volume is significantly reduced. If the water temperature is too low, the diesel fuel will rise slowly at the combustion room temperature, the flame retardation period will be long, the combustion process will deteriorate, and the running performance will be poor.
In the piston group, there are also possible causes. First, the 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 blocked by thermal expansion when the engine is working, and it will be tightly pressed against the cylinder wall, or the piston ring will break, and it will be easy to pull out the groove on the cylinder wall. Secondly, the piston pin sprang out. Because the piston pin circlip is not installed or falls off or breaks, the piston pin bounces out during the movement, it is easy to strain the inner wall of the cylinder, causing the cylinder to blow-by to the crankcase. Then, the cylinder clearance of the piston is too small or too large. If the material of the piston is poor, the manufacturing size error is too large, or the piston is deformed after the piston pin is assembled, the clearance between the piston and the cylinder is too small, the piston will be stuck after being heated and expanded, and the cylinder wall will be strained. The fourth point is that the piston ring is severely deposited. Excessive carbon deposits cause the piston ring to stick or seize in the ring groove. At the same time, the carbon deposits are a hard abrasive that will grind into longitudinal grooves on the cylinder wall. Finally, the piston is severely biased. Due to the bending and twisting of the connecting rod, the deviation of the parallelism and coaxiality of the connecting rod journal, main journal, and piston pin seat is too large, causing the piston to be obviously biased, which will accelerate the wear of the piston ring, piston and cylinder wall, and destroy the oil film formation.
The reason for the cylinder liner is as follows. The roundness and cylindricity tolerances of the cylinder liner exceed the allowable range, which greatly reduces the seal between the piston and the cylinder liner. The high-temperature gas in the cylinder moves down, destroys the oil film between the piston and the cylinder wall, and causes the cylinder to pull. The cylinder liner is deformed during assembly. For example: the upper end of the cylinder liner protrudes too much, the cylinder liner is deformed after installing the cylinder head; the cylinder liner water blocking ring is too thick, and the cylinder liner is deformed after being pressed into the body, which will easily cause the cylinder to pull.
Improper use can also cause cylinder pull.
The air filter is not sealed, which makes the filtering effect worse. The dust, sand and other impurities in the air are sucked into the cylinder to form abrasive wear. Tests have shown 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.
Poor running-in. For new or overhauled engines, there are many microscopic irregularities on the surface of cylinder liners, pistons, piston rings and other parts, making it difficult to form a lubricating oil film. If it is put into high-load operation immediately without running-in, it is easy to cause accidents such as cylinder pulling.
Start at low temperatures often. When the engine is started at low temperature, the lubricating oil has high viscosity and poor fluidity, and it is difficult to form an effective oil film on the inner wall of the cylinder. Engine maintenance WeChat: fadongjiweixiu According to the test of the research department, the wear of cylinder liners and other parts of the diesel engine when the cooling water temperature is below 30°C is 5 to 7 times that of normal water temperature.
The engine is overheating. When the cooling system is poorly maintained or overloaded, excessive engine temperature not only reduces the mechanical strength of the parts, but also prevents the formation of a 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. The result is often that the piston is partially melted and the inner wall of the cylinder liner is damaged, forcing the engine to stall.
In actual use, cylinder pulling is often the result of several factors. For example, if an engine that has not been run-in is started, it is immediately put into full-load operation, and it is prone to cylinder pulling accidents.