The current farm machinery repair points, due to the technical level and the limited equipment, equipment, and lack of repair experience, the axle bush assembly can not guarantee the quality requirements, making the engine more and worse. To this end, the problem of axle bush assembly is discussed. 1. the clearance of the bearing bush is determined. In order to ensure good lubrication, there must be a suitable gap when the crankshaft journal and bearing bush are matched. The clearance of the bearing bush mainly depends on the relative sliding speed of the shaft and bearing bush, the magnitude of the bearing load, the oil clearance and the contact diameter and length of the bearing bush. When the shaft is stationary in the bearing bush, the shaft is tightly attached to the bearing, and the lubricating oil on the lower contact surface is almost completely squeezed out. When the shaft begins to rotate, the oil film is wedged into the contact surface under the effect of the friction (viscosity) of the lubricating oil itself, and there is a certain amount of heat to make the shaft deflect and float, the greater the effect is with the increase of the speed. The force acting on the shaft and the load acting on the journal are equal, the shaft and the bearing bush enter into the liquid lubrication state, and the shaft and the bearing bush are completely separated from the lubricating oil. At this point the shaft and the shaft wear the least. The clearance between bearing shells is too large or too small, which is bad for lubrication. The clearance is too small, the oil film is too thin, the bearing bush temperature is as high as 150 degrees Celsius, the lubricating oil becomes thinner, and the adsorption capacity is reduced. When the journal and bearing bush continue to slide relatively, and the temperature increases, it is easy to cause tile burning and other accidents. When the clearance is too large, oil leakage occurs between the bearing bushes, the oil pressure drops, and the engine has percussion noise. From the above, it is not difficult to see that the assembly gap of the axle bush is too large or too small, so there must be a suitable gap to make the engine work well and prolong the service life of the axle bush. The journal and bearing bush can be inspected by visual method and measuring tool before installation. There should be no scratches, cracks and non - limit ellipticity on the surface of the neck of the shaft; the surface of the bearing alloy is not shedding or damaged, and the bearing of the tile and the tile seat has a proper tightness. When the Bush clearance is within the allowable range, the shaft neck and axle bush surface and the oil path are cleaned, the oil road is unblocked, and the oil is gently pressed in the tile seat of the main shaft tile back, and the crankshaft is installed in the man-machine body after a little oil is applied to the working surface of the axle bush. The connecting rod can be installed on the connecting rod journal according to the technical requirements. When the crankshaft journal and axle bush need to be repaired, it can be boring according to the shaft, grinding the neck of the shaft, and then selecting the same grade bearing bush and bearing the bearing bush after the standard clearance. Use the inner diameter meter to measure the actual size of the axle bush hole, leave the standard clearance, and then grind the crankshaft journal according to the appropriate size of the requirement, but it does not exceed the limit of the repair size of the shaft. In this way, the dimension accuracy of the shaft is easy to control, and the manufacturing accuracy of the tile is retained, so that the assembly clearance of the bearing bush can be ensured reliably. When installing the bearing bush, a layer of lubricating oil is first coated on the inner diameter of the bush so as to ensure the lubrication of the internal combustion engine when it is cold and running. According to the test, the wear rate of the internal combustion engine during cold start is 60% to 80% of the total wear. When the axle bush is installed at the same time, the required torsion moment is required to ensure that the axle bush is not loose in the working state; the connecting rod axle bush has a "positioning lip", and the two positioning lips are installed in the corresponding grooves on the large head of the connecting rod and the connecting rod cover, so as to prevent the axle bush from turning and moving in the axial direction. The thin walled Bearing Bush should be fully fastened so that the back of the tile can be tightly attached to the seat hole to improve the heat dissipation effect and improve the stress distribution. The gap between 1. spindle tiles is 0.06 to 0.11 mm, the wear limit is 0.25 mm, the clearance of the connecting rod is 0.06 to 0.105 mm, the wear limit is 0.30 mm, and the axial clearance of the crankshaft is 0.10 to 0.20 mm (adjusted by the gasket). The tightening torque of the 2. connecting rod nut is 80~100 N. M. 3. if manual scraping is done, the contact area between the journal and the bearing bush is not less than 85%, and the contact is uniform. The alloy thickness of the 4. axle bush is not less than 0.30 mm. 5. the bearing bush and the tile seat should be fitted with proper tightness, and the ellipticity of the journal is not overrun. In order to ensure the close fitting of the axle bush and the tile seat, the axle bush should have the correct geometry and the appropriate height, put the axle bush on the shaft neck, and the clearance between the axle bush and the axle neck should be in accordance with the regulations. 1. calculation method: the diameter of the axle neck and the bearing bush hole can be measured separately by the inner diameter meter and the outer diameter micrometer, and the algebraic difference of the two diameter is the clearance of the bearing bush. The gap between the axle bush and the axle neck of the small tractor is 0.05 to 0.11 mm, and the gap between the axle bush and the neck of the large tractor is 0.1 ~ 0.17 mm, and the end face of the axle bush should be 0.05 to 0.10 mm higher than the seat plane. If it is too high, it can be repaired by filing. If it is too low, the bearing bush must be replaced again. 2. experience method: when checking the gap of the connecting rod, the two ends of the crankshaft are supported, and the connecting rod is mounted on the neck of the shaft according to the regulations. The connecting rod is hard to shake the small end of the connecting rod, and the connecting rod should rotate about two circles around the axis. When the spindle clearance is checked, the crankshaft is installed in the man-machine body, and the flywheel is rotated by hand. The shaft does not shake and rotate freely.