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General requirements of diesel engine assembly technology
  • Automotive

The assembly of diesel engine is a very important process in the repair of diesel engine. The quality of diesel engine assembly determines the repair quality of diesel engine to a great extent. Even if the qualified parts are not installed according to the requirements of assembly process, the original performance of the product can not be achieved. Therefore, attention must be paid to assembly work in agricultural machinery maintenance. (1) the assembly precision of the diesel engine is very high. Before assembly, we must understand the structure principle of diesel engine and the assembly relationship of each component, carefully clean the parts, check the parts and assembly to ensure the quality of the diesel engine. Ensure the cleaning of equipment, tools and work site. (2) it is necessary to ensure the quality of the parts, components and general Chengdu to be tested and tested. Easily damaged parts and fasteners, such as cylinder pad and other liner, bolt, nut, lock piece, opening pin, lock wire and so on. All the parts used in one time can not be reused. No scratches and burrs are allowed on the working surfaces of the parts with clearance fit. Check and thoroughly clean the cylinder body and the lubricating oil path on the crankshaft, and clean it with compressed air to ensure smooth flow. (3) the nuts and bolts used by the diesel engine can not be replaced at will. To ensure that the bolt system used is used (metric or customary), the size and grade are exactly the same as when they are disassembled. The locking parts for bolts and nuts, such as pin, washers, locking plates and so on, shall be assembled in a complete and reliable manner and shall not be omitted or damaged. (4) the installation of the lock must pay attention to the skill. The brake paw and the reverse side of the lock should be inserted into the shaft groove and the edge of the nut respectively; the inner diameter of the spring washer is in accordance with the diameter of the bolt, and the distance is approximately 2 times that of the thickness of the gasket; for pairs of fixed bolts, the holes can be drilled on each face of each bolt head, and the steel wire is worn through the hole on the head of the bolt when tightened. Make it interlocked with each other. The locking wire is often used in the screw group to prevent loosening of the screws. When installing, it is important to note that when the screw is loose, the stay wire should be tightened, otherwise it will not work. (5) parts and components that are marked with each other should be assembled in a certain direction and mark, and should not be misplaced, such as crankshaft and flywheel, timing of ignition timing, etc., must be aligned according to the mark, and must not be misplaced. (6) it is necessary to make clear the nature and requirements of parts coordination and master the technical standards of interference fit and clearance coordination. When the relationship of parts can not be guaranteed, it will affect the performance of the diesel engine and even cause serious damage to some parts. There should be a certain radial clearance between the crankshaft main shaft neck and the main shaft tile, the connecting rod shaft neck and the connecting rod bearing, so that the oil can form the oil film on the friction surface when the crankshaft is rotated, thus ensuring the good lubrication of the shaft neck and the axle bush. Excessive or too small clearance will cause bad lubrication on the friction surface. (7) assembly parts with interference fit and clearance should be assembled according to the required assembly process strictly. When interference fit parts are assembled, grease should be first applied to prevent parts from being damaged. Generally, the press method is used to assemble parts, so that the surface of the parts should not be hammered by the hammer, so as to avoid damaging parts and mating surfaces. If it is to be used, it can be struck lightly with soft hammers of copper or wood or the chopping board made of copper. For the fitting parts with large interference, the heating jacket can be used during assembly. No scratches and burrs are allowed on the working surfaces of the parts with clearance fit. The important clearance of the key parts must be reasonably guaranteed, such as the gap between the piston and the cylinder wall, the gap between the neck of the spindle and the neck of the connecting rod, the axial clearance of the crankshaft, the camshaft, the clearance of the valve and so on. (8) during the assembly process, all sports parts should be checked whether there is any motion incompatibility between different parts. Do not wait for the inspection after all loading. Check the side assembly to make sure the fault is located. Sliding bearings and journal surfaces and relatively moving friction surfaces should be coated with oil when assembling. When installing the oil pump and the oil filter, fill the engine oil. (9) the bolts or screws that are fixed for the main parts should be replaced when they are deformed, elongated and slipped; when the studs are installed, the key bolts and nuts for the order and torque should be tightened in accordance with the prescribed order and torque. Strictly according to the prescribed tightening torque and tightening sequence, fastening the threaded connections, such as connecting rod bolts, main bearing bolts, cylinder head bolts and other important bolts should be fastened according to the specified moment; the bolt group must be divided, cross and uniformly tighten, for example, the cylinder head bolts should be divided, cross and mean from the center to the diagonal line from the central to the four sides. Keep it tight. (10) the sealing part should prevent "three leakage", that is, oil leakage, leakage and leakage. Three the cause of leakage is generally due to the failure of the assembly process, or the wear, deformation, aging and corrosion of seals. The quality of sealing is often related to the selection, pretightening degree and assembly position of sealing materials. All disposable seals must be replaced once they are dismantled. In the process of assembling diesel engines, there are many places that need to be sealed. For example, to prevent air leakage between cylinder head and cylinder, prevent leakage and leakage of pump shaft and shell. The main means of sealing is to install sealing material and sealant at the junction. Pressure tests are required for the good or bad sealing. For the parts that have been coated with sealed fasteners before the factory, it is necessary to remove the residual glue and oil, and seal or fasten the sealed fasteners when they are reinstalled. (11) the weight of the crankshaft can not be interchanged; the quality difference of each cylinder piston and connecting rod group can not be greater than the allowable value, so as to avoid the severe vibration during operation. (12) when installing the engine, pay attention to the recovery of all pipelines (such as oil tubing, hydraulic pipe, activated carbon tank tube, coolant and refrigerant tube, brake fluid tube, vacuum tube) and all conductors, and enough clearance between all moving parts and heating components. (13) in the assembly process, special tools should be used as far as possible to prevent damage to parts.

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