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Diesel engine cylinder pulling inspection and prevention

Jul 21, 2018

Diesel engine cylinder pulling inspection and prevention


Diesel engine cylinder, refers to the cylinder wall along the direction of piston running a series of different depth grooves. This is in the case of no foreign matter, because when the outer surface of piston ring slides in contact with the cylinder surface, high temperature is generated on the smallest surface, which leads to the ignition and bonding between the piston and cylinder wall, and when the heat generated by burning and welding dissipates, carbide is generated on the piston ring. Like a sharp knife, this carbide or fused, sticky product cuts off the metal on the cylinder wall, creating irregular grooves of varying depth and depth.


Take the example of a drawing cylinder accident of 4115J diesel engine. After the overhaul of the machine, the cylinder sleeve, piston and piston ring were replaced. When the final assembly is finished and the initial grinding occurs, the cylinder will be pulled and then shut down. After opening the cylinder cover, it was found that there were serious scratches on the cylinder wall of II and III cylinders. The piston connecting rod set was removed and adhesive and longitudinal scratches were found on the head and piston rings of the two pistons (the scratches were most serious at the intersection of the parallel lines with the center line of the crankshaft).


In order to further determine the cause of the cylinder, the following steps are followed: first, the cylinder inner wall of the grinding cylinder is repaired; Remove the piston rings of II and III cylinders, assemble the piston ring connecting rod into the cylinder and tighten the bearing cover of the connecting rod according to the specified torque. The II and III cylinder pistons were placed at the top and bottom points respectively. After checking the matching clearance between the piston and the cylinder inner wall, it was found that there was no clearance between one side of the head and the other side of the skirt and the cylinder wall (the direction of the center line of the crankshaft) at the top and bottom stops of the two cylinder pistons. It can be seen that the II and III cylinder pistons have severe longitudinal inclination in the cylinder. Remove the crankshaft and check the center line of the crankshaft. As a result, the bending degree of the crankshaft is within the allowable range. Remove the II and III cylinder links and check the bending and distortion of the links. After checking the replacement cylinder sleeve of the machine, it was found that the wear amount of cylinder sleeve of II and III in the longitudinal direction was greater than that of other directions, and was also greater than that of the other two cylinders in the same direction.


According to the above inspection results, it can be concluded that the connecting rod of the II and III cylinders of the machine has been bent in the operation before the overhaul, resulting in the "partial cylinder" phenomenon of the two cylinder pistons in the work. At that time, there was enough wear and tear between the cylinder sleeve, piston and piston ring, no serious cylinder was formed. When the overhaul of cylinder liner, piston, piston ring in the new, smaller gap between piston and cylinder liner components, connecting rod bending slanted the piston in the cylinder, piston components between the cylinder wall and the contact stress of local produce too much, cause the contact surface of the oil film is destroyed, the piston, piston ring and cylinder liner wall local basically in a state of dry friction. The high temperature caused by friction makes the metal on the contact surface fuse and stick. This state in a short period of time and no improvement, that is, the formation of the above - mentioned cylinder accident.


The disposal method is: replace the piston, piston ring and cylinder sleeve of II and III cylinders; The adjustment test of connecting rod was carried out. After the assembly, carefully check the mating gap between the piston and the cylinder sleeve, and conduct the grinding test again.


As far as the author knows, in some small machinery repair enterprises, when carrying out the overhaul of engineering machinery vehicles, the maintenance technology of engines is often not standard enough. In the process of repair, especially after some parts are replaced, the necessary inspection and measurement are ignored, and the process of assembly cannot be operated strictly according to the rules, thus causing the accident that could have been avoided as mentioned in the above example. For this reason, according to the current equipment and technical conditions of some repair factories, in order to ensure the repair quality of the engine, in addition to the appropriate acquisition of necessary maintenance equipment, the following aspects should be paid special attention to:

(1) in each link of the repair process, attention should be paid to civilized production. Avoid random knock during engine disassembly and assembly. Mark parts that are still ready to be used after disassembly; Properly placed in the prescribed way to prevent deformation.


(2) attention should be paid to the cleaning of new parts to be installed. All parts of the engine are more or less impurities on the surface and inside during the manufacturing process, and must be carefully cleaned before assembly and final assembly. If mechanical impurities on the surface or inside of the parts enter the surface of the moving parts without cleaning, they will not only accelerate the wear on the surface of the moving parts, but even block the oil passage in serious cases, causing the movement of the moving parts to lag.


(3) after engine failure, careful inspection and measurement should be carried out for important parts, whether they are ready to be replaced or continue to be used. In this case, if the worn condition of the old cylinder sleeve is checked before replacing the new cylinder sleeve and the bending condition of the connecting rod is tested, abnormal wear and causes of individual cylinder can be found in time, and the accident can be avoided.


(4) in the process of assembly, it is necessary to operate in strict accordance with the assembly process rules, especially pay attention to the inspection and measurement of various clearance (such as the clearance of main bearing and connecting rod bearing, etc.). In this case, if the piston of each cylinder is first examined without a piston ring according to the regulations, the deflection of the piston of II and III cylinders in the cylinder can be detected in time without cylinder pulling accident.


(5) after the completion of the engine assembly, the engine shall be inspected and adjusted in strict accordance with the requirements of the manual. For valve timing and valve clearance, diesel fuel delivery advance Angle, injection pressure, ignition advance Angle of engine and other important technical data, not by experience operation (such as some repair personnel have to adjust the valve clearance measure without feeler, but because of who I am with hand estimate valve clearance if appropriate), should be strictly guarantee the technical parameters comply with the provisions of the manual.


(6) the structure of the engine or parts of the engine shall not be changed at will during repair. The structural parameters and configuration of engine components are determined according to the specific technical requirements of the engine model in the design of the engine, which has a strict scientific basis. Random changes will inevitably affect the technical parameters and normal operation of the engine. In a repair factory, because the driver reflects that the engine power cannot be removed, the repair personnel will grind the combustion chamber volume in the cylinder head to increase the compression ratio, thus increasing the compression pressure and explosion pressure of the machine. However, the result of this will inevitably lead to the increase of the mechanical load of the engine and affect the service life of the engine. There is also a repair factory, in order to solve the problem of high cooling water temperature in the engine operation, it is one-sided to think that the thermostat is installed in the cooling pipe and is removed without permission. In this way, the cooling water temperature will be low for a long time, which will increase the thermal stress of combustion chamber parts. In particular, it is easy to cause low temperature corrosion on the inner surface of cylinder liner and increase wear.


(7) for engines that have been overhauled or replaced with major moving parts, the grinding test shall be conducted in accordance with the specifications or other technical data. It is strictly prohibited to operate at full load without grinding. According to the author's opinion, the key to improve the repair quality of the engine is to improve the technical quality of the repair personnel. Especially with the rapid development of science and technology today, new technologies, new materials, new processes and new structures have been widely used. If we do not pay attention to the training and knowledge update of technical personnel, the repair quality cannot be guaranteed, and it is even difficult to complete the normal maintenance of some new types of machines.