Fault analysis of engine crankshaft rolling bearings
2026-07-20
Some small wheeled tractors use two rolling bearings to support their engine crankshafts. A rolling bearing consists of an inner ring, an outer ring, rolling elements, and a cage. Raceways are located on the outer side of the inner ring and the inner side of the outer ring to facilitate the rolling of the rolling elements. The inner ring mates with the shaft, and the outer ring mates with the bearing housing or casing. Normally, the inner ring rotates with the shaft, while the outer ring does not.
After the crankshaft's front and rear main journals are fixed to the inner ring of the rolling bearing, the outer ring of the rolling bearing is secured to the bearing housing bore in the engine block using a rear bearing cap to prevent axial movement. The outer ring of the front bearing is directly installed in the housing bore in the engine block without axial fixation, allowing for axial expansion and contraction due to crankshaft thermal expansion.
Failure of the rolling bearings on the engine crankshaft directly affects the engine's technical condition. Therefore, rolling bearing failures should be taken seriously. Common rolling bearing failures are analyzed below: worn, deformed, or broken rolling bearing cages; splash lubrication of crankshaft bearings; insufficient or no lubricating oil in the bearing, especially under heavy loads, causing the bearing temperature to rise. The temperature of the inner ring of the bearing is about ten degrees Celsius higher than that of the outer ring. Due to the difference in thermal expansion between the inner and outer rings, the clearance between the balls and the raceway disappears, making the cage prone to breakage during bearing operation. Therefore, clean lubricating oil should be applied to the raceway during bearing installation to prevent dry friction caused by insufficient lubricating oil splashing.
Increased radial and axial clearances in the bearing, besides dry friction and excessive wear during startup, are mainly caused by friction between the rolling elements and raceways from metal particles on the surface of the parts and sand, dust, and dirt in the lubricating oil. Abrasive wear significantly increases the clearance between the bearing rings and rolling elements, resulting in a dull surface and uneven scratches on the raceway. Prevention methods include timely lubrication oil changes and ensuring the oil filler hole is sealed to prevent contaminants from entering.
Wearing between the inner and outer rings and the mating parts creates clearance, causing the inner ring of the bearing to move. The inner ring of the rolling bearing uses an interference fit with the journal. The maximum interference fit of the front bearing inner diameter is 0.055mm, and the minimum interference fit is 0.012mm. The maximum interference fit of the rear bearing inner diameter is 0.046mm, and the minimum interference fit is 0.003mm. Based on these fits, if the bearing has been disassembled and reassembled several times, a gap may appear between the bearing inner ring and the journal. In this case, the journal must be repaired before use.
Bearing outer ring movement. For ease of disassembly and assembly, the rolling bearing outer ring and housing bore use an transition fit. The maximum interference fit of the front bearing outer ring is 0.035mm, and the maximum clearance is 0.013mm. The maximum interference fit of the rear bearing outer ring is 0.016mm, and the maximum clearance is 0.06mm. The housing bore must be measured during assembly; the interference fit or clearance must not exceed the above ranges. Otherwise, the housing bore must be repaired.
When the bearing and shaft fit becomes loose, some repairmen may use knurling or punching to roughen the surface of the loose shaft, attempting to achieve a tight fit. This not only disrupts the geometry of the shaft surface, causing the bearing to misalign during installation, but also results in the fuzzy areas eventually being flattened, leading to a loose fit. The correct repair method is to first grind the journal, followed by brush plating or spraying. When assembling the inner and outer rings of a rolling bearing, a large interference fit can cause the bearing balls to become stuck in the housing rings, easily damaging the bearing cage during operation. Therefore, measurements should be taken during assembly to ensure a standard interference fit.
Peeling occurs on the raceway and rolling element surfaces of a rolling bearing due to hard particles falling into the mating surfaces of the housing or between the shaft and the rings, causing distortion of the raceway shape. The rolling elements exert the greatest pressure on this area, resulting in rapid wear and metal spalling of the raceway. Rolling bearings are highly precision components and are extremely sensitive to foreign objects. During maintenance, a clean, lint-free cloth should be used. Old cotton fibers should never be used, as the loose threads can easily get into the lubricating oil and enter the bearing, which is extremely harmful. Before assembly, the journal, housing bore, and inner and outer ring surfaces of the bearing must be thoroughly cleaned to prevent dirt from entering the mating surfaces.
Sparing is caused by impact loads and alternating stress. The rolling elements and raceways of the inner and outer rings of the bearing are subjected to periodic pulsating loads, resulting in periodically changing contact stress. When the number of stress cycles reaches a certain value, fatigue sparing occurs on the working surfaces of the rolling elements or the inner and outer ring raceways. Excessive bearing load will exacerbate this fatigue. Additionally, improper bearing installation or shaft bending can also cause raceway sparing. Counterweights on the engine flywheel and pulleys generate rotational inertial torques that balance the rotational inertial torques generated by the rotating parts of the engine. If these inertial torques are not balanced, the engine will vibrate significantly after ignition, increasing alternating stress and the number of stress cycles, leading to premature sparing of the raceway and rolling element surfaces. To prevent spalling of the raceway and rolling element surfaces, avoid additional loads and undue vibration during use. Use throttle and speed appropriately during operation to prevent tractor jolting. Regularly check the fixing bolts to prevent loosening.
Damage caused by raceway damage during installation. If the pressure applied during installation is transmitted through the outer ring and steel balls, pits will inevitably form at the contact points between the raceway and the steel balls. These pits are the root cause of damage, escalating rapidly and causing the bearing to spall and become unusable in a very short time. Therefore, use specialized tools during disassembly, and ensure that force is applied correctly and evenly.
After the crankshaft's front and rear main journals are fixed to the inner ring of the rolling bearing, the outer ring of the rolling bearing is secured to the bearing housing bore in the engine block using a rear bearing cap to prevent axial movement. The outer ring of the front bearing is directly installed in the housing bore in the engine block without axial fixation, allowing for axial expansion and contraction due to crankshaft thermal expansion.
Failure of the rolling bearings on the engine crankshaft directly affects the engine's technical condition. Therefore, rolling bearing failures should be taken seriously. Common rolling bearing failures are analyzed below: worn, deformed, or broken rolling bearing cages; splash lubrication of crankshaft bearings; insufficient or no lubricating oil in the bearing, especially under heavy loads, causing the bearing temperature to rise. The temperature of the inner ring of the bearing is about ten degrees Celsius higher than that of the outer ring. Due to the difference in thermal expansion between the inner and outer rings, the clearance between the balls and the raceway disappears, making the cage prone to breakage during bearing operation. Therefore, clean lubricating oil should be applied to the raceway during bearing installation to prevent dry friction caused by insufficient lubricating oil splashing.
Increased radial and axial clearances in the bearing, besides dry friction and excessive wear during startup, are mainly caused by friction between the rolling elements and raceways from metal particles on the surface of the parts and sand, dust, and dirt in the lubricating oil. Abrasive wear significantly increases the clearance between the bearing rings and rolling elements, resulting in a dull surface and uneven scratches on the raceway. Prevention methods include timely lubrication oil changes and ensuring the oil filler hole is sealed to prevent contaminants from entering.
Wearing between the inner and outer rings and the mating parts creates clearance, causing the inner ring of the bearing to move. The inner ring of the rolling bearing uses an interference fit with the journal. The maximum interference fit of the front bearing inner diameter is 0.055mm, and the minimum interference fit is 0.012mm. The maximum interference fit of the rear bearing inner diameter is 0.046mm, and the minimum interference fit is 0.003mm. Based on these fits, if the bearing has been disassembled and reassembled several times, a gap may appear between the bearing inner ring and the journal. In this case, the journal must be repaired before use.
Bearing outer ring movement. For ease of disassembly and assembly, the rolling bearing outer ring and housing bore use an transition fit. The maximum interference fit of the front bearing outer ring is 0.035mm, and the maximum clearance is 0.013mm. The maximum interference fit of the rear bearing outer ring is 0.016mm, and the maximum clearance is 0.06mm. The housing bore must be measured during assembly; the interference fit or clearance must not exceed the above ranges. Otherwise, the housing bore must be repaired.
When the bearing and shaft fit becomes loose, some repairmen may use knurling or punching to roughen the surface of the loose shaft, attempting to achieve a tight fit. This not only disrupts the geometry of the shaft surface, causing the bearing to misalign during installation, but also results in the fuzzy areas eventually being flattened, leading to a loose fit. The correct repair method is to first grind the journal, followed by brush plating or spraying. When assembling the inner and outer rings of a rolling bearing, a large interference fit can cause the bearing balls to become stuck in the housing rings, easily damaging the bearing cage during operation. Therefore, measurements should be taken during assembly to ensure a standard interference fit.
Peeling occurs on the raceway and rolling element surfaces of a rolling bearing due to hard particles falling into the mating surfaces of the housing or between the shaft and the rings, causing distortion of the raceway shape. The rolling elements exert the greatest pressure on this area, resulting in rapid wear and metal spalling of the raceway. Rolling bearings are highly precision components and are extremely sensitive to foreign objects. During maintenance, a clean, lint-free cloth should be used. Old cotton fibers should never be used, as the loose threads can easily get into the lubricating oil and enter the bearing, which is extremely harmful. Before assembly, the journal, housing bore, and inner and outer ring surfaces of the bearing must be thoroughly cleaned to prevent dirt from entering the mating surfaces.
Sparing is caused by impact loads and alternating stress. The rolling elements and raceways of the inner and outer rings of the bearing are subjected to periodic pulsating loads, resulting in periodically changing contact stress. When the number of stress cycles reaches a certain value, fatigue sparing occurs on the working surfaces of the rolling elements or the inner and outer ring raceways. Excessive bearing load will exacerbate this fatigue. Additionally, improper bearing installation or shaft bending can also cause raceway sparing. Counterweights on the engine flywheel and pulleys generate rotational inertial torques that balance the rotational inertial torques generated by the rotating parts of the engine. If these inertial torques are not balanced, the engine will vibrate significantly after ignition, increasing alternating stress and the number of stress cycles, leading to premature sparing of the raceway and rolling element surfaces. To prevent spalling of the raceway and rolling element surfaces, avoid additional loads and undue vibration during use. Use throttle and speed appropriately during operation to prevent tractor jolting. Regularly check the fixing bolts to prevent loosening.
Damage caused by raceway damage during installation. If the pressure applied during installation is transmitted through the outer ring and steel balls, pits will inevitably form at the contact points between the raceway and the steel balls. These pits are the root cause of damage, escalating rapidly and causing the bearing to spall and become unusable in a very short time. Therefore, use specialized tools during disassembly, and ensure that force is applied correctly and evenly.
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