The main and connecting rod bearings on the engine are one of the precision components, but as the operating time increases, the bearings may experience fatigue peeling, mechanical damage, and burning, which not only affects the normal operation of the engine, but also greatly reduces the service life of the bearings. Common damage to bearing bushing should be analyzed on a case by case basis to eliminate potential faults and extend their service life to ensure normal engine operation.
1. Burn tiles
Burnout refers to the phenomenon where the oil film between the main journal and bearing bushing of the crankshaft, or between the connecting rod journal and bearing bushing, is broken due to a lack of oil lubrication or a small gap, causing direct contact between the bearing bushing and the surface of the journal, resulting in dry friction and causing adhesion or even biting.
1.1 Reason
(1) Lack of oil. Oil pump failure, insufficient oil pressure; Oil passage blockage, dirty or blocked collector or filter, and ineffective bypass valve; The assembly of bearing bushing is too tight or too short, the bearing seat rotates, and the oil passage is blocked, resulting in a lack of lubricating oil in the bearing bushing and causing them to burn out.
(2) The clearance between the bearing bushing and the journal is too large, resulting in low oil film pressure; The clearance between the two friction surfaces is too small, or the protrusion of the bearing is too high, causing deformation of the alloy at the bearing opening. During operation, the area of direct contact between the two friction surfaces is much larger than the specified value, causing a sharp increase in friction heat and resulting in the burning of the bearing.
(3) The roundness and cylindricity of the crankshaft journal exceed the tolerance and cannot form an oil film.
(4) The crankshaft is bent or the main bearing hole is too different from the center.
(5) The engine is overloaded for a long time and overheats.
(6) The surface was not coated with lubricating oil during assembly.
2.2 Exclusion methods
After burning the bearing, it is necessary to replace the bearing and grind the crankshaft journal. And the bending of the crankshaft, the bending of the connecting rod, and the concentricity of the crankshaft main bearing seat hole should be checked. If the allowable value is exceeded, correction and repair should be carried out.
2.3 Prevention
It is to start from the cause of the burning of the bearing, ensure good lubrication, and strictly follow technical standards and operating regulations to assemble the bearing.
2. Alloy detachment on the working surface of the bearing bushing
After running for a period of time, a circular groove pattern is formed on the crankshaft journal and bearing surface of the diesel engine. There is a certain amount of powdered bearing alloy, other types of metal and non-metallic impurities in the oil.
2.1 Reason
(1) The engine oil is not clean. During the machining process of diesel engine cylinder blocks, crankshafts, and other parts, metal shavings are left in the cylinder blocks, crankshafts, oil pumps, and oil passage holes, as well as on the walls of the cylinder body. Metal shavings, molding sand that have not been thoroughly cleaned before assembly, and dust and impurities that remain inside the diesel engine due to not being cleaned thoroughly during assembly.
(2) The surface roughness of the shaft neck is poor, or it is not run in according to the specifications. During the running in period, it is overloaded at high speed, causing the surface of the bearing to be pulled.
(3) Before leaving the factory, a layer of rust proof oil was brushed on the surface of the crankshaft bearing bushing. Before assembly, it is necessary to clean and remove the rust proof oil to prevent it from being diluted by heat and mixed with the lubricating oil of the diesel engine during operation, which increases impurities in the oil and accelerates its deterioration.
(4) The sintering between the bearing alloy and the steel back is not strong, or due to the high-speed and overload of the diesel engine, the alloy on the working surface of the bearing may delaminate and fall off.
(5) The groove on the working surface of the crankshaft journal or bearing bushing causes sharp metal or non-metallic debris between the journal and bearing bushing, resulting in "cutting" when the journal and bearing bushing move relative to each other.
2.2 Preventive measures
(1) Use high-quality lubricating oil, regularly check the oil quality, and replace it promptly if dilution or deterioration is found.
(2) Strictly follow the operating procedures, use the vehicle correctly, and try to avoid heavy, low-speed, and overloaded operation.
(3) Strictly follow the repair process regulations and pay attention to the cleanliness of parts during assembly; Select bearing bushing according to specifications and strictly check the clearance between the bearing bushing.
3. Corrosion of bearing bushing
3.1 Reason
Corrosion is generally caused by impure lubricating oil, which contains chemical impurities (such as acidic oxides) that invade the bearing alloy. The generation of oxides is mainly the result of high-temperature oxidation of engine oil. When the oil temperature is below 150 ℃, corrosion is slower.
3.2 Preventive measures
To prevent corrosion of the bearing bushing, attention should be paid to the temperature of lubricating oil and cooling water during use, and the engine should not operate at high temperatures. To ensure the cleanliness of the lubricating oil and ensure that the lubricating oil filtering device is working properly, it is necessary to regularly clean the oil filter, replace the filter element, and replace the new oil regularly.
4. Excessive clearance between bearing bushing and journals
4.1 Phenomena
The clearance between the bearing bushing and the journal is too large, and the bearing bushing will make a strange noise during engine operation. The sound of connecting rod bearing bushing is a gentle and short tapping sound, which is small or absent at idle, clear at medium speed, intense at high speed, and has a clear and continuous "dang" tapping sound when accelerating suddenly, with no change in temperature. The abnormal noise of crankshaft bearing bushing is a heavy and muffled "clang clang" knocking sound, which is more muffled than the sound of connecting rod bearing bushing. The higher the engine speed, the greater the dynamic response.
4.2 Diagnosis
During diagnosis, a stethoscope can be used to sequentially touch the upper part of the crankcase and listen carefully. As the speed gradually increases, the noise increases from small to loud, and it is louder than the crankshaft bearing bushing. When the oil filler cap is opened, the abnormal knocking sound can also be heard, and in severe cases, it can be heard next to the engine. The faster the speed, the louder the sound, and when suddenly accelerating, it becomes more prominent, continuously producing a knocking sound. A driver can be used to short circuit the suspected spark plug to ground. If the sound decreases or disappears, and a "dang" sound is made when the driver is suddenly moved away, it can be concluded that the connecting rod bearing bushing is making a noise. If the connecting rod bearing bushing of two cylinders make a noise, use a screwdriver to short circuit the spark plug of one cylinder, and the noise will be reduced; Short circuit the spark plugs of two cylinders with two drivers, and the sound disappears, indicating that the connecting rod bearing bushing of these two cylinders are noisy.
In most cases, there is no need to use a screwdriver to make crankshaft bearing bushing sound, but using a screwdriver to short circuit can sometimes reduce the noise. Usually, based on experience, the direction of the sound can be used to determine which crankshaft bearing bushing has abnormal noise, and after identifying it, the bearing bushing can be repaired. The erosion or detachment of the crankshaft bearing bushing not only enhances the sound when increasing the engine speed, but also results in lower body vibration?. The radial clearance of the crankshaft bearing bushing or journal is too large due to wear. When hearing a sound, the oil pressure decreases rapidly, and the reading value on the oil gauge is not enough.
4.3 Exclusion
If there is or is confirmed to be a crankshaft bearing bushing noise, the crankcase must be removed and the bearing bushing and its clearance checked. If the bearing bushing is worn beyond the limit or burned out, it should be replaced; If the gap is too large, the corresponding level (repair size) of the bearing should be adjusted or replaced.
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