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Inspection and repair of engine crankshaft deformation
  • Automotive

The crankshaft is one of the core components of the engine, and all the power of the engine is output through it. In addition, through the gear transmission in its free end, it reaches the timing of gas distribution, timing of oil supply and other auxiliary devices, so if the crankshaft fails, it can not be done as required, and the engine will not work properly. Crankshaft deformation is one of the common damage of crankshaft. Crankshaft deformation refers to the bending and torsion of the crankshaft. The obvious part of crankshaft bending deformation is the middle spindle neck. If crankshaft continues to be used after bending, it will accelerate the wear of crankshaft connecting rod mechanism and even cause cracks and breakage of crankshaft. Therefore, it must be tested in engine repair. (1) the work of the diesel engine is not stable, and the stress of each journal is unbalanced. (2) the diesel engine suddenly overloaded, causing the crankshaft to vibrate excessively. (3) diesel engine often has "burst" combustion, causing crankshaft often subjected to impact load. (4) the quality of repair and assembly is low, and the clearance between crankshaft bearing and connecting rod bearing is too large, and the work is impacted. (5) the crankshaft bearing is loose and the centerline is not in a straight line. (6) the ignition time of the gasoline engine is too early or the spark plug often has one or two fires. (7) the additional inertia force and inertia moment caused by the imbalance of the piston connecting rod group or the balance iron and the flywheel cause the vibration of the unit to be large. (8) the crankshaft end gap is too large, and it moves before and after operation. (9) the distortion of the crankshaft, most of which is caused by individual piston cylinder, such as small plug gap, or too big expansion after the piston is heated, so that the piston movement resistance is too large, and even the cylinder will lead to the crankshaft distortion. In tractor trailers, excessive start and emergency braking do not step down the clutch and other reasons, will cause distortion of the crankshaft. To prevent the crankshaft deformation from the cause of the deformation of the crankshaft, it is mainly to improve the operation level, avoid the excessive impact load, maintain and maintain in time, in order to ensure that the engine is always working in good working conditions, and to improve the quality of repair and assembly. The crankshaft bending test can be done on the crankshaft grinder or on the platform by using "V" type iron to set up the crankshaft and check with the dial indicator. When checking the bending, put the dial indicator pin on the middle spindle neck and make the pointer to the zero dial of the positive dial. Then slowly rotate the crankshaft for a week, then half of the pointer's swing on the dial indicator is the crankshaft's straightness. The straightness of the crankshaft should not be greater than 0.05 mm. If it is greater than this value, but still within 0.1 mm, the straightness can be eliminated by combining with axle neck grinding. When the straightness is greater than 0.1 mm, the cold pressing straightening must be carried out. When checking crankshaft distortion, the crankshaft should also be placed on "V" iron or installed on the top of machine tool. The two axis neck of the same connecting rod, such as the I, VI cylinder and connecting rod neck of 6 cylinder crankshafts, the I of the 4 cylinder crankshaft, the neck of the VI cylinder connecting rod shaft, is located at the top stop point, and then the height of the two connecting rod neck in the same horizontal plane is measured with a height percentage, and the height difference is the crankshaft distortion. The greater the difference, the greater the twist angle. If the twist angle is greater than 30 degrees, the correction should be carried out. When the crankshaft is slightly distorted, it can be eliminated by grinding the surface of the journal. If the distortion is large, it must be corrected separately. There are varying degrees of bending deformation of the crankshaft repaired by the overhauls factory. Generally speaking, the deformation of crankshaft is plastic deformation in a small range. Even so, crankshaft straightening must be carried out. The straightening of the crankshaft should meet the following requirements: first, the coaxiality and the allowable runout of the crankshaft are required to meet the requirements; second, the technical performance of the crankshaft is not reduced after straightening; third, the bending rate of the crankshaft should not exceed 1. 5mm/m. It is more risky to correct crankshaft with bending rate greater than 1. 5mm/m. 1. cold pressure correction applies the crankshaft to the main shaft of the V type iron frame, pressurizing from the opposite direction, and placing a copper block between the pressure head and the spindle neck. As the crankshaft is elastic, the bending load should be 10~15 times that of the crankshaft and 2 min, and the pressure will be removed again. If the bending capacity is greater than 1 mm, the fractional correction should be made so as not to cause a reverse deformation due to excessive pressure. The effect of cold pressure correction is not stable enough, and the original deformation is easy to recover when the crankshaft works. At the same time, it will produce plastic deformation and residual internal stress on the surface of the journal, resulting in stress concentration. 2. percussion correction for the crankshaft with little curvature can be corrected by "surface knocking" method. According to the direction and degree of crankshaft bending, a ball hammer or a hammer can be used to strike the left and right sides of the crankshaft arm to make the crankshaft arm deformation, so that the axis of the crankshaft will be displaced and the purpose of correcting the crankshaft is achieved. 3. on the machine calibration, the cylinder block is placed on the working platform, and the old bearings (tiles) are placed on the front and rear two bearing bases, and the intermediate bearings are removed. Add a little lubricating oil on the bearing, then put the crankshaft on the edge of the cylinder and dial indicator. Turn the crankshaft gently with the hand, measure the maximum position of the bending in the middle shaft neck, mark with chalk, cushion the soft aluminum or other soft items of the bearing cover, hold the shaft neck, and slowly tighten the crankshaft bearing cover bolt. When the time is about 1H, bolt is released and calibrate with dial indicator. If not, the calibration is continued until the requirement is met. The 4. hot top pressure method is added a pressure bolt between the crank arm of the bend. According to the size of the straightness, the top pressure is pressed to the opposite direction of the bending, and the concrete top bend is so large that it should be determined by actual experience. Then, on the two side crank arm of the top bolt, the blower is uniformly heated to about 300 degrees Celsius. After the crankshaft is cooled, the top pressing bolt is removed and the crankshaft straightness is checked. Repeat so until the crankshaft is straightened. The purpose of the above heating is to accelerate deformation, stabilize straightening effect and reduce residual deformation, thereby reducing elastic recovery. 5. grinding straightening method for crankshaft with straightness greater than 0.06 mm or less than 0.10 mm is usually straightened in the grinding process of crankshaft. The above methods of straightening crankshaft only apply to integral crankshaft, but not to combined crankshaft.