Cause analysis of damage of connecting rod and crankshaft of Weichai engine
Connecting rod tile, crankshaft tile abnormal wear, or lock shaft diameter, is due to insufficient lubricating oil pressure or supply, or the oil film between the bearing bush is not formed, in the crankshaft journal and shaft bush between the semi-dry friction or dry friction lead to engine bearing bush melting, melting, crankshaft is locked by the bearing bush. How did this happen? I summarize the following points:
1 Improper use. When the loader engine is overloaded for a long time, the temperature of lubricating oil increases, the viscosity of lubricating oil decreases, the oil pressure is low, and the oil film is not formed between the crankshaft and the crankshaft tile. Heat generated by friction can not be taken away, resulting in increased friction and wear, resulting in malignant wear and melting of bearing bush.
The loader does not start normally in winter. In winter, when the ambient temperature is below 0 degrees, the engine is quickly forced to start. At this time, due to the low temperature and high oil viscosity, the lubricating oil film between the shaft and the bearing bush has not been formed, resulting in the melting of the bearing bush. Winter starter engine should be stopped after the engine is first started. The purpose is to allow the oil pump to send oil to the oil channel. After a pause of 1-3 minutes, start the engine until ignition. The revolution is 650R /min, and the running time is about 5 minutes. Wait for oil pressure and water temperature to increase before letting the loader work.
3. Oil film is difficult to form. If the quality of lubricating oil is too poor or the service life is too long, it is not replaced in time, or because of other reasons, the oil quality deteriorates, the formation of oil film is destroyed, causing the engine bearing bush to be melted. It should be noted here that sometimes the injector is stuck, so that the China diesel engine injector into the cylinder is not atomized, and then the combustion is insufficient or not burning, so that the excess diesel oil flows into the oil bottom along the cylinder wall, so that the oil is diluted, the viscosity becomes low, and the oil film is difficult to form. When checking the dipstick, there will be a great diesel smell, and the oil surface will rise accordingly. In addition, internal leaks in diesel pumps can cause this to happen.
4 Serious oil shortage. Oil plays four major roles in operation, namely lubrication, cooling, sealing and anticorrosion. If the oil level is insufficient, the oil is seriously insufficient. Due to insufficient lubrication and cooling, the engine bushing temperature of the loader rises suddenly, the bearing bush and crankshaft journal expand and deform, the gap disappears, and the direct contact between metals becomes more serious. The lubricating oil on the crankshaft journal is burned off, resulting in a sharp rise in the temperature of the engine bearing bush, and the burning of shingles is inevitable.
5 Assembly problem. The gap between the journal and bearing bush and bearing bush lubrication relationship is the largest. The small clamping clearance of bearing bush will restrict the flow of lubricating oil, make it difficult for oil to enter, make the friction heat can not be taken away well, and increase the possibility of bearing deformation and burning tile failure; Excessive bearing clearance will reduce the arc length of the bearing bush and journal, greatly increase the pressure load of the oil film, aggravate the fatigue of the bearing bush, and increase the vibration impact of the crankshaft. The lubricating oil is extruded, losing the adhesion of the oil film, increasing the wear of the bearing bush. Just to remind you, if the crankshaft has a burning tile failure,
(The gap between spindle tile and spindle neck is 0.095--0.163mm, and the gap between connecting rod bearing and connecting rod journal is 0.059--0.127mm)
(2) Bearing bush wear bearing bush generally occurs in the instant lack of lubrication or lubricating oil instantaneous interruption. Its performance characteristics are bearing bush and journal surface direct metal contact, there are stains and serious scratches. There are two main reasons for bearing scratches. One is the use of the problem, the second is the quality of lubricating oil.
1 Use questions. Mainly after the engine starts, in the case of no increase in temperature and pressure, a few seconds after starting to mention high speed. Because this way does not form enough oil flow, the bearing bushing lubrication is insufficient and scratches appear. After the engine starts, it takes about 15-40 seconds for the oil to fill the engine oil channel, and 3-8 seconds of forced acceleration to reach the maximum speed. If you force the highest speed after starting the engine, the bearing bush will be short of oil for about 8 seconds and run at a high speed with load. The bearing bushing will be taut. It will wear out very quickly.
2. Lubricating oil quality problems. Dust in lubricating oil. Many impurities, long service time is not timely replacement; Concrete mixer engines are often under high load. High temperature operation, oil impurities increase, will cause bearing bush scratch. The key is the impurity of the lubricating oil. .
(3) There are cracks in the bearing alloy and engine bushing of stirring truck, which may be caused by unreasonable use of alloy shedding and cracking, which can also be called "Jun" cracking. This is due to the frequent direct contact between the bearing bush and the journal, resulting in increased temperature and reduced fatigue strength in the bearing bush. The cracks are in a network. When the engine is running, the liquid pressure in the crack causes the crack to develop until the bearing bush lining flaps off and gradually expands. This is also known as the "exploding tile" phenomenon. Due to the spalling of the alloy block, the gap between the journal and the bearing bush becomes larger, the wear of the two is aggravated, and the lubricating oil is pressed down from the gap.
The main cause of cracking and peeling of bearing tiles is operational problems. The connecting rod of the engine is much larger than the oil film pressure and load of the main bearing. It is easy to cause fatigue under the alternating load of periodic changes. At the same time, the link is affected by the oil pressure drop first, especially the last link. At the end of the lubricating oil loop, the final lubrication is obtained. Drivers often start the engine repeatedly, forcing the maximum speed before the oil pressure rises, putting more load on the links and greater linear speed, so the bearings are slightly pulled. Injured. Scratches become cracks and finally flakes. So be careful in operation: after the engine starts, it must be idle for 3-5 minutes. Do not force speed adjustment before the oil pressure is low.
(iv) Excessive wear of bearing bushing Excessive wear occurs in the case of instantaneous oil shortage and repeated occurrence. Each time, the metal is lubricated with oil and in direct contact. This time is not long, the temperature rise of the bearing bush is not enough to cause discoloration and overheating of the bearing bush, but every time the metal is in direct contact, there will be a part of the bearing alloy is worn off. The gap increases, over time, repeatedly caused excessive wear of the bearing bush, so that the oil pressure is reduced, leading to the final operation.
The main reasons for excessive bearing bush wear are as follows:
1. The engine works continuously when the oil level is too low, and does not refuel in time;
2, after the engine starts, do not increase the oil pressure, force to increase the speed;
3. The oil filter element is not qualified, and the filter element is seriously blocked and cannot be replaced in time;
4, engine oil temperature is too high;
5, the oil grade does not match;
6, air filter dirty or air filter shell is not sealed;
