Automotive engine sliding bearing maintenance features and precautions

Maintenance features of modern automotive engine sliding bearings 1. Thin-walled bushings do not allow the previous car engine crankshaft main bearing, connecting rod bearing new bearing must be scraped, scraping only to ensure the ideal contact area. In fact, modern automotive engine crankshaft bearing and bearing rod bearings wear-resistant alloy coating are very thin, high dimensional accuracy of processing, the surface roughness is very low, the general does not allow scratch repair. Only by the appropriate size matching; if there is no suitable size of the crankshaft bearings, if necessary, can be used to grind the base hole grinding crankshaft, in order to obtain the appropriate fit clearance. In order to adapt to this situation, should be used according to the size of the bearing bush grindstone neck method to change the past with the shaft with tile approach. There is also a three-tier alloy bearing, steel back is made of copper-lead alloy surface layer. Surface alloy thickness is generally 0.02-0.03mm, is coated with copper plating on the lead-alloy, which is to improve the performance of copper-lead alloy bearing surface, if the scraping will lose this role, undermining the original design. Currently widely used scraping tile and boring tile and other processes should be gradually directed to the direction of the final assembly of finished tile transition. In the past with the method of scraping watts check bearing, bearing and journal contact surface points required full, evenly distributed, reaching more than 75% of the total bearing area, and tightness appropriate. Now use boring or direct assembly of the bearing bush without processing, in which case the size of the gap is mainly used, and check the contact imprint and tightness at the same time, but sometimes the imprinting is slightly less than 75%, which is also allowed, but it should be noted that Require uniform contact, not on one side. Bearing wear, not padded back pad. Bearing bush and bush seat are two parts. After assembly, the work should be like a part. Because the bearing bush is thin-walled, in order to ensure the correct geometric shape when working, the machining accuracy Very high, the surface roughness value is very low, if in the meantime pad of paper, is bound to undermine their correct fit, and paper is a poor conductor of heat, is not conducive to the bearing heat, so the paper may cause total loss system Oil temperature is too high, and even cause burning tile accident. Similarly, in the tile back pad copper skin is not allowed. In addition, the bearing assembly is not allowed to loose, but after the pad back cushion things, it is easy to loose, thus undermining the normal operating conditions of the bearing. In fact, padding on the tile back will destroy its original gap with the crankshaft so that the contact area and mating tightness are not guaranteed. When the internal combustion engine operates, it will cause the bearing pad to loosen and damage the oil film between the shaft and the tile. Its thermal conductivity and lubrication performance decline, and will have a boundary friction, and even caused by the bush burn and killed on the crankshaft. 2. Thin-walled bearing face A lot of modern automotive engine bearings designed with thinned end face structure. For example liberation of CAl091 automobile main bearing face 8mm range, along the entire length of both sides of the bearing thinning 0.015-0.035mm. Because the bearing assembly has a certain amount of interference, the interface may cause a small amount of deformation, the deformation will undermine the bearing lubrication and working conditions, in order to avoid this effect, the modern engine widely used in the interface near the local thinning Bearing, but also equal to open a small vertical section of the groove, is conducive to the uniform distribution of lubricating oil on the bearing surface and out of impurities. In the auto repair shop, if you use their own cast bearing, processing should make the above structure to ensure the normal operation of the bearing to ensure the quality of engine repair. 3. Locating the back of the bearing bush also has to prevent the rolling bush bearing bush bearing seat at work required reliable positioning, neither allow rotation, does not allow movement, does not allow vibration. Overhaul tile back grinding was found to be smooth, indicating a loosening phenomenon. However, the key measures for the reliable positioning of the bearing pad are proper interference, not the function of the positioning lip. The function of the positioning lip lies in the initial positioning during assembly. 4. Crankshaft tape tightness adjustment In fact, the crankshaft tape should maintain a certain degree of tightness, if the tape is too tight, will not only result in increased transmission resistance, but also cause the pump shaft, fan shaft and alternator shaft deformation, or even bearing acceleration damage. 5. Bearing According to the choice of load bearing lubricant overload and light load of the points, all have to add calcium-based grease lubrication is not correct. Light-duty bearings can be filled with grease, heavy-duty bearings must use gear oil. Heavy-duty bearing grease lubrication, if the continuous operation under heavy load, the working temperature is higher than 100 ℃ above, will make the water in the grease gradually evaporated, most of the base oil is separated to form a soap, and its liquidity Poor, can not play the role of lubrication, and heavy-duty bearings using gear oil, still has a higher viscosity at high temperatures will not be due to centrifugal force from the contact surface is thrown off, and the oil film at high pressure strength is still Higher, can form a good lubrication. 6. Crankshaft and connecting rod bearing alloy thickness tends to be thinner Crankshaft and connecting rod bearing design, tend to thin the alloy layer as much as possible. A relatively thin bearing alloy layer, when used, has a much more uniform, and much less, internal stress than a thick bearing alloy layer. In general, the shear force between the layers of the alloy can be reduced to none, resulting in a significant improvement in surface fatigue. After testing, comparing the different thickness of the bearing, found that the thin layer of the most durable alloy, the bonding situation is also good. Crankshaft and connecting rod bearing alloy thickness, recommended for Babbitt alloy 0.25-0.4mm, such as Beijing BJ2020 automotive alloy bearing thickness of 0.30-0.35mm; copper-lead alloy in the 0.4? 0.8mm range. The bearing alloy thickness does not include the amount of scraping. Bearing bore scraping to keep, bearing width less than 40mm, scraping amount 0.08-0.llmm; bearing width of not less than 40mm, scraping amount of 0.07-0.11mm. 7. Bearing bush or bearing sleeve and journal to leave a certain gap between the clearance of the sliding bearing radial clearance and axial clearance of two. Radial clearance and top clearance and side clearance; axial clearance is also called the amount of shaft movement. First of all, the radial clearance is the minimum condition for the shaft and the bearing to move freely. Second, the radial clearance is the guarantee of the operation accuracy of the control shaft. Of course, the smaller the radial clearance, the higher the running accuracy of the shaft, but can not arbitrarily reduce the radial clearance, the radial clearance is too small, not only difficult to form a lubricating film, and may lead to the burning of tile hold shaft accident; Third, radial Gap is an important condition for the formation of liquid lubrication, especially the dynamic pressure bearing, lubricating oil film formation mainly by the wedge-shaped gap between the shaft and the bearing. Radial clearance points top clearance and side clearance, the former value is about twice the latter. These two clearances are necessary for the wedge-shaped oil film formed between the journal and the bearing. To leave a certain axial gap, which refers to the axis of the movement of the gap, is divided into the thrust gap and expansion gap. Thrust clearance is for thrust bearings, is to allow some axial play and leaving the gap. Expansion gap is the bearing radial load, in order to ensure the free expansion of the shaft leaving the gap. The size of the gap is related to the accuracy of the machine during operation. The smaller the radial clearance is, the higher the precision is. However, when the clearance is reduced to a certain extent, liquid lubrication can not be guaranteed. The gap is too large, there will be beating in the rotation, it can not form a stable oil film lubrication. Therefore, the radial clearance values ​​can not be provided, should be consistent with the technical requirements of the machine. Radial clearance of sliding bearings is very important, too large, too small are extremely harmful. The gap is too large, the bearing oil film is difficult to form, can not guarantee the liquid lubrication, and will reduce the accuracy of the operation of the machine, even lead to severe vibration and noise, can cause serious accidents; gap is too small, the lubricating film is difficult to form, Will also produce high fever, severe accidents can occur. Sliding bearings to leave the axial gap, is to make the shaft in the temperature change free retractable room. In general, in order to improve the operating accuracy of the shaft, axial clearance smaller appropriate. But it can not be too small, the axial clearance is too small, high temperature during operation may produce bites, or even damage the bearings, an accident. Sliding bearing (tile) grinding and scraping China's internal combustion engine bearings, there are generally three categories: Xi-base Babbitt bearings, copper-lead alloy bearings and aluminum bearings. After normal use of the pad will inevitably occur after the gap increases, usually after about 1500h wear the tile about 0.0l5mm. However, if used improperly, the amount of wear and tear of the tile will also rapidly increase, causing the machine to work abnormally. Therefore, it is necessary to periodically check and adjust the clearance of the bearing pad so as to meet the requirements. When crankshaft sliding bearing (tile) is repaired, the upper bearing cap shall be tightened with the specified torsion force and the inner diameter dial indicator shall be used to check the roundness of the bearing seat hole. If more than 0.05mm, surfacing welding at both ends of bearing cap or Shims to adjust. The new bearing into the seat hole, the bearing cap nut tighten, and then loosen a nut, with a feeler gauge gap should be 0.05-0.1mm. Too high to file a little, too low should be re-matching. In the case of lack of material, the back of the bearing pad and bearing the same size can be the same thickness of copper skin. The back of the bearing must be clean and smooth and the positioning projection should be undamaged. If it is found that the inner circle with the contact surface of the bearing does not meet the requirements, the inner circle of the bearing should be scraped, and then check