Once the rolling bearing of the engine crankshaft fails, it will directly affect the technical state of the engine. Therefore, attention should be paid to the failure of the rolling bearing. The common failures of the rolling bearing are now analyzed as follows: 1. There is a gap between the movement of the inner and outer rings of the bearing and the wear of the mating parts

①. The outer ring of the bearing moves around. In order to facilitate disassembly and assembly, the outer ring of the rolling bearing adopts a transitional fit with the seat hole. The maximum interference of the outer ring of the front bearing is 0.035mm, and the maximum clearance is 0.013mm. The maximum interference of the outer ring of the rear bearing is 0.016mm, and the maximum clearance is 0.06mm. When assembling, the seat hole should be measured, and its interference or clearance should not exceed the above range, otherwise the seat hole should be repaired.

②. The inner ring of the bearing moves around. The inner ring of the rolling bearing adopts an interference fit with the journal. The maximum interference of the inner diameter of the front bearing is 0.055mm, and the minimum interference is 0.012mm. The maximum interference of the inner diameter of the rear bearing is 0.046mm, and the minimum interference is 0.003mm. From the above coordination point of view, if the bearing has been disassembled and assembled several times, there may be a gap between the inner ring of the bearing and the journal, the journal must be repaired before it can be applied.

When the fit between the bearing and the shaft is loose, some maintenance workers use embossing or punching the surface of the loose shaft to fluff the surface of the shaft in an attempt to obtain a tight fitting surface. This not only destroys the geometric shape of the shaft surface, makes the bearing not get the correct center position during installation and skews, but also the fluffed part will eventually be flattened and become a loose fit. The correct maintenance method is to grind and repair the journal first, and then brush or spray the journal.

2. The rolling bearing cage is worn, deformed or broken

①. When assembling the inner and outer rings of the rolling bearing, due to the large amount of interference, the bearing balls are stuck in the seat ring, and the bearing cage is easily squeezed during operation. Therefore, measurement should be performed during assembly to ensure standard interference.

②. The lubrication of the crankshaft bearing is splash type. When the bearing lacks or has no lubricating oil, especially when the load acting on the bearing is large, the bearing temperature rises. In general, the temperature of the inner ring of the bearing is about 10°C higher than that of the outer ring. Because the thermal expansion of the inner and outer rings is different, the gap between the ball and the raceway disappears, and the cage is likely to squeeze when the bearing is running. Therefore, when installing the bearing, clean lubricating oil should be applied to the raceway to prevent the lubricating oil from splashing and causing dry friction.

3. The rolling bearing raceway and rolling element surface peeling

①. Peeling caused by impact load and alternating stress. The rolling elements of the bearing and the inner and outer ring raceways are all subjected to cyclic pulsating loads, resulting in cyclically changing contact stresses. When the number of stress cycles reaches a certain value, fatigue spalling occurs on the working surfaces of the rolling elements or inner and outer ring raceways. If the bearing load is too large, this fatigue will increase. In addition, if the bearing is installed incorrectly and the shaft is bent, the raceway may peel off. The flywheel and pulley of the engine are equipped with counterweights, and the rotational moment of inertia produced is balanced with the rotational moment of inertia produced by the rotating part of the engine. If the generated moment of inertia is not balanced, the engine will vibrate greatly after fire, which will increase the number of alternating stresses and stress cycles, causing the raceway and rolling element surfaces to peel off prematurely.

In order to avoid spalling on the surface of the raceway and rolling elements, additional load and undue vibration should be avoided during use, the throttle and speed should be used reasonably during operation to prevent the tractor from bumping, and the fixed body bolts should be checked frequently to prevent loosening .

②. Because the external hard particles fall on the matching surface of the shell or between the matching surface of the shaft and the ring, the shape of the raceway is distorted. The rolling element puts the greatest pressure here, resulting in rapid wear and metal peeling of the raceway of the ring. Rolling bearing is a very precise part, which is very sensitive to foreign matter. In the maintenance process, use a clean, non-linting wiper cloth. The wiper cloth must not be replaced with old cotton yarn, because the yarn ends in the old cotton yarn are easily mixed into the lubricating oil and enter the bearing, which is very harmful. Before assembling, thoroughly clean the journal, seat hole, and inner and outer ring surfaces of the bearing to prevent dirt from entering the mating surface.

③. Damage caused by damage to the raceway during installation. If during installation, the applied pressure is transmitted through the outer ring and the steel ball, it will inevitably cause pits in the part where the raceway of the ring contacts the steel ball. The bearing peeled off and scrapped in a short time. Therefore, special tools should be used when disassembling, and the force-bearing parts should be correct and even.

4. The radial and axial clearance of the bearing increases

The radial and axial clearances of the bearings increase, except for dry friction and excessive friction and wear during start-up. It is mainly caused by the friction between the metal particles on the surface of the parts and the sand, dust and dirt in the lubricating oil on the rolling elements and raceways.

The bearing has a significant increase in the clearance between the ring and the rolling elements due to abrasive wear, a matte surface has been formed on the raceway, and uneven scratch marks have appeared. The prevention method is to replace the lubricating oil on time, and the lubricating hole should be airtight to prevent the entry of dirt.​