Repair and maintenance is an effective means to restore the performance of special vehicles and extend their service life. However, in the actual operation process, some users and maintenance personnel have a lot of wrong practices, which affect the normal use of special vehicles. The normal use of special-purpose vehicles.
1, Avoid oil only add not change
Oil is essential in the use of diesel engines, mainly for lubrication, cooling, cleaning and other functions. Therefore, many drivers will pay attention to check the amount of lubricating oil and add it according to the standard. However, they neglect to check the quality of lubricating oil and replace the deteriorated oil, resulting in some engine moving parts always running in poor lubrication environment, thus accelerating the wear and tear of the parts. The wear and tear of the engine parts is accelerated. Under normal circumstances, the loss of oil is not large, but it is easy to contaminate, thus losing the role of protecting the diesel engine. In the process of diesel engine operation, many dirt (fuel incomplete combustion generated In the process of diesel engine operation, many dirt (carbon soot, carbon and dirt, etc.) will enter into the engine oil. For new or overhauled machinery, after the test run impurities will be more, if only add not change on the rush into use, it is easy to cause Burning tile, holding shaft and other accidents. In addition In addition, even if the replacement of oil, some drivers due to lack of maintenance experience or to save trouble, will not be thoroughly cleaned when replacing the oil, so that mechanical impurities still remain in the oil pan and oil circuit.
2, Do not use the butter indiscriminately coated
(1) cylinder gasket. Apply grease on. Grease is commonly used in the repair of construction machinery grease, can play the role of lubrication and sealing. Therefore, some repairers in the installation of the cylinder gasket, it will be in the cylinder pad on a layer of grease, think this can increase the diesel engine seal. I do not know, but this affects the performance of the diesel engine. The cylinder gasket is the most important seal between the cylinder block and the cylinder head of the diesel engine. The most important seal, it can not only seal the cylinder generated by the high temperature and high pressure gas, but also can seal the cylinder head and cylinder body of cooling water and lubricating oil, so in the disassembly and installation of the cylinder pad, are to pay special Pay attention to its sealing quality. If the installation of the cylinder pad on the grease, when the cylinder head bolts tighten, part of the grease will be squeezed into the cylinder waterway and oil channel, stay in the cylinder pad between the grease in the When the cylinder is working, due to the high temperature, part of it will flow into the cylinder and burn, and the other part will be left on the combination of cylinder body and cylinder cover, which will make a gap between the cylinder gasket, cylinder cover and the plane of the body, High temperature and high pressure gas is easy from here to impact the cylinder pad, destroy the cylinder pad, causing gas leakage. In addition, grease for a long time in a high temperature state will also produce carbon, causing premature aging of the cylinder gasket deterioration. Therefore Therefore, do not apply grease when installing cylinder gasket.
(2) Tire nuts greased. In order to easily tighten the nuts and prevent rust, many mechanics grease the lug nuts on the tires. In fact, this is a wrong practice. Because the tire nuts screwed After tightening, the inter-threads have the characteristic of self-locking. This is due to the fact that the thread helix angle is smaller than the equivalent friction angle between the threads. In a given bolt joint, the helix angle of rise is a certain value, while the equivalent friction angle varies with the friction state between the threads. Obviously, the equivalent friction angle between the threads decreases after oiling, and the self-locking performance of the bolt joint becomes worse. Therefore, never apply lubricating grease or drip lubricating oil on the bolts and nuts of tires. grease or lubricant. If you do so, the nut will be loosened and even cause an accident.
3, Avoid cylinder liner and piston new products
Without optional installation in the change of cylinder liner and piston, think that the new cylinder liner and piston are standard parts, are interchangeable, installed on it can be used. In fact, the size of cylinder liner and piston In fact, the size of cylinder liner and piston have a certain tolerance range. If the largest size of cylinder liner with the smallest size of the piston, it will make the clearance too large, resulting in compression force, starting difficulties. Therefore, when changing, you must must check the standard cylinder liner and piston size grouping code, the installed cylinder liner and piston must make the standard piston size grouping code and the standard cylinder liner size grouping code, only then can ensure that the two have a standard fit clearance. In addition, each cylinder installed with the same grouping code of cylinder liner and piston, but also pay attention to the installation before the inspection of the cylinder plug clearance, in order to ensure that the assembly standard, in In order to ensure the assembly standard, a test should be carried out before installation to prevent the installation of counterfeit and defective products.
4, Avoid not checking the plunger stroke margin
In the irony test of piston injection pump, many maintenance personnel do not pay attention to check the stroke margin of the plunger. The so-called plunger travel margin refers to the amount of movement that can continue to go up after the plunger is topped by the cam on the camshaft to the upper stop. The reason for checking the travel allowance after adjusting the oil supply start time is that the travel allowance of the plunger is related to the wear of the plunger and the sleeve. After the plunger and sleeve are worn, the plunger has to move up a bit more before the oil supply can start, thus delaying the oil supply start time. When the adjusting bolt is unscrewed or replaced with thicker adjusting pads and gaskets, the lowest position of the plunger is moved up, so that the plunger stroke margin is reduced. Therefore, in the maintenance and commissioning of the injection pump, the first step should be to check this stroke margin to determine whether the injection pump is still allowed to adjust. When checking, the following different methods should be used according to the different structures of the injection pump: a) Turn the camshaft and remove the oil valve and valve seat after the plunger is topped to the upper stop, and measure with the depth vernier. b) After the plunger is topped to the upper stop, pry up the spring seat of the plunger spring with a screwdriver to make the plunger rise to the most point. Then use the thickness gauge to measure between the lower plane of the plunger and the tappet adjusting bolt. The standard travel allowance of the plunger is about 1.5mm, and the limit travel allowance after wear should be not less than 0.5mm.
When measuring the cylinder clearance, it fails to measure in the direction of the piston skirt perpendicular to the piston pin hole, but in other directions. The structure of aluminum alloy piston is characterized by small and large, cone, and Local section is elliptical, so the cylinder clearance along the circumference of the direction is not equal. Measurement, the provisions of the ellipse in the direction of the long axis clearance, that is, the measurement of the piston skirt perpendicular to the direction of the piston pin hole gap. This measurement is more convenient, accurate, and in the reciprocating motion, the piston skirt perpendicular to the direction of the piston pin hole due to lateral pressure and wear, so, measuring the cylinder clearance Therefore, the cylinder clearance should be measured in the direction of the piston skirt perpendicular to the piston pin bore.
6, Avoid piston open fire heating
Because the piston and the piston pin is interference with, so in the installation of the piston pin, should first make the piston heat expansion, at this time, some maintenance personnel will put the piston on the open fire directly heated, such a practice is very wrong, because the piston parts of uneven thickness, the degree of thermal expansion and contraction will be different, open fire heating will make the piston unevenly heated, easy to cause deformation; piston surface will also be attached The surface of the piston will also adhere to the carbon ash, reducing the service life of the piston. If the piston reaches a certain temperature and then cools naturally, its metallurgical organization will be damaged and the wear resistance will be greatly reduced, and its service life will be significantly shortened. In the installation of the piston pin, the piston can be placed in the hot oil evenly heated to make it slowly expand, do not use the open flame to directly add heat.
7, Avoid using sanding cloth to polish the shaft tile
For some inexperienced repairers, shaft tile is a difficult job, because the scraping technology is difficult to master, so it is not easy to achieve the technical requirements of the shaft tile, for this reason, some people in the replacement of the shaft tile. When changing the shaft tile, in order to increase the contact area between the shaft tile and the crankshaft, use the sanding cloth grinding to replace the scraping tile. This method is extremely undesirable in the actual maintenance, because the abrasive grain on the sand cloth is hard, while the shaft tile Alloy is soft, so that when grinding sand particles are easily embedded in the gold, diesel engine will accelerate the wear of the journal, shortening the service life of the crankshaft.
8, Avoid tightening the bolts too tight
Construction machinery in the process of disassembly, many parts of the bolt are required torque requirements, such as transmission, cylinder head, tires, connecting rods and front axle parts, tightening torque in the manual The tightening torque is specified in the manual, and should not be changed at will. However, many users mistakenly believe that tighter will be safer, but tightening too much will cause the screw or bolt to break, and may also cause failure due to thread slippage. cause failure.
9, Avoid tire pressure is too high
Wheeled construction machinery tire inflation pressure is an important factor in determining its service life and efficiency. Tire pressure is too high or too low will affect its service life, but also not conducive to safe driving Especially in the hot summer. The scientific inflation standard should be: the standard tire pressure as the benchmark, with the change of temperature, the tire pressure is slightly adjusted to the right. For example: summer should be 5%-7% lower than winter 5%-7% lower, because taking into account the high temperature in summer, the gas is heated, the pressure increases, on the contrary, winter must reach the standard air pressure or slightly lower.
10, Do not add cold water suddenly when the tank is boiling
Engine overload operation, heat dissipation or tank water shortage will cause the water tank boiling, at this time, if you immediately add cold water, it will lead to cylinder head and cylinder block frying. Therefore, once found in use Water tank boiling, should take emergency measures to stop the operation, so that the diesel engine cooling water to cool down on their own.