Maintenance is an effective means to restore the performance of special vehicles and extend their service life. However, in the actual operation process, some use and maintenance personnel have many wrong practices, affecting the normal use of special vehicles.
1, avoid oil only increase
Oil is essential in the use of diesel engines, mainly for lubrication, cooling, and cleaning. Therefore, many drivers will pay attention to check the amount of oil, and add according to the standard, but they ignore the inspection of the quality of the lubricant and the replacement of the already deteriorating oil, resulting in some engine parts are always in poor lubrication Run in the environment to accelerate the wear of all components. Under normal circumstances, the loss of oil is not great, but it is very easy to pollute, thus losing the role of protecting the diesel engine. During the operation of the diesel engine, many contaminants (soot, coke, fouling, etc. resulting from incomplete combustion of fuel) will enter the engine oil. For new or overhauled machinery, there will be more impurities after commissioning. If you only add it and you are eager to put it into use, it is very easy to cause accidents such as burning tiles and holding shafts. In addition, even if the oil is changed, some drivers may not clean the oil passage completely during the replacement due to lack of maintenance experience or plans, so that mechanical impurities still remain in the oil pan and the oil passage.
2, avoid butter mess with smear
(1) Grease the cylinder pad. Butter is a grease commonly used in the repair of construction machinery and can act as a lubricant and seal. Therefore, some repairmen apply a layer of butter to the cylinder pad when installing the cylinder pad, which is believed to increase the tightness of the diesel engine. As everyone knows, this will affect the performance of the diesel engine. The cylinder head gasket is the most important seal between the diesel engine cylinder block and the cylinder head. It not only seals the high temperature and high pressure gas generated in the cylinder, but also seals the cooling water and lubricant in the cylinder head and cylinder body. When installing the cylinder head gasket, pay special attention to its sealing quality. If the cylinder pad is greased during installation, when the cylinder head bolts are tightened, part of the butter will be squeezed into the cylinder water channel and the oil channel. When the grease remaining in the cylinder pad is working in the cylinder, due to the influence of high temperature, part of the grease will flow. The human cylinder burns, and the other part remains on the joint surface between the cylinder block and the cylinder head, which creates a gap between the cylinder pad, the cylinder head and the plane of the machine body. The high temperature and high pressure gas can easily impact the cylinder pad from this, destroying the cylinder pad, causing leakage. gas. In addition, the butter will produce carbon deposits at high temperatures for a long time, resulting in premature aging and deterioration of the cylinder mat. Therefore, do not apply butter when installing the cylinder head gasket.
(2) Apply butter to tire nuts. In order to easily tighten the nuts and prevent corrosion, many repairmen apply oil to the bolts and nuts of the tires. This is actually a wrong practice. Because the tire nut is tightened, there is a self-locking feature between the threads. This is because the thread helix angle is smaller than the equivalent friction angle between the threads. For a given bolt connection, the helix angle is a certain value, and the equivalent friction angle varies with the friction between the threads. Obviously, after the oil coating, the equivalent friction angle between the threads decreases, and the self-locking performance of the bolt connection deteriorates. Therefore, never apply grease or dripping lubricant to the bolts and nuts of the tire. Doing so will make the nut loose and even cause an accident.
3, avoid cylinder sleeve and piston new products without installation
When replacing cylinder liners and pistons, the new cylinder liners and pistons are considered to be standard parts. They are interchangeable and can be used when they are installed. In fact, there is a certain tolerance range between the size of the cylinder liner and the piston. If the cylinder with the largest size is equipped with the piston with the smallest size, the fitting gap will be too large, resulting in weak compression and difficulty in starting. Therefore, the standard cylinder sleeve and piston size grouping code must be checked when reloading. The cylinder sleeve and the piston must be assembled so that the standard piston size grouping code is the same as the standard cylinder sleeve size group code. Only in this way can the two be guaranteed. With standard fit clearance. In addition, cylinders and pistons of the same grouping code should be installed at the same time, and cylinder plug clearance must be checked before installation. In order to ensure assembly standards, a test should be performed before installation to prevent the installation of counterfeit products. .
4, bogey does not check the plunger stroke margin
In the satirical test of a plunger-type fuel injection pump, many maintenance personnel did not pay attention to checking the stroke allowance of the plunger. The so-called plunger stroke margin refers to the amount of movement that the plunger can continue to ascend after it is top-dead-centered on the camshaft. After adjusting the start time of fuel supply, the reason why the travel allowance is also checked is because the stroke allowance of the plunger is related to the wear of the plunger and the sleeve. After the plunger and sleeve are worn out, the plunger must move upwards for a while to start oil supply, thereby delaying the start of oil supply. When the adjustment bolt is screwed out or replaced with a thicker adjustment pad or spacer, the lowermost position of the plunger moves upwards, so that the stroke margin of the plunger is reduced. Therefore, when repairing and debugging the fuel injection pump, it is firstly necessary to check the travel allowance to determine whether the injection pump also allows adjustment. During the inspection, the following different methods should be used according to the different structures of the fuel injection pump: a) Turn the camshaft, push the plunger to the top dead center, remove the oil valve and valve seat, and measure with a deep vernier. b) After the plunger is topped to the top dead center, use a screwdriver to pry the spring seat of the plunger spring to raise the plunger to the highest point. Then use a thick gauge inserted between the plunger lower plane and the tappet adjustment bolt to measure. The standard travel distance of the plunger is about 1.5mm, and the limit stroke after wear is not less than 0.5mm.
5, avoid cylinder gap measurement is not allowed
When measuring the cylinder gap, it cannot be measured in the direction perpendicular to the piston pin hole of the piston skirt, but measured in other directions. The structural characteristics of the aluminum alloy piston is that it is small and large, it is a cone, and the partial section is oval, so the cylinder gap along the circumferential direction is not equal. During the measurement, it is specified that the clearance in the direction of the long axis of the ellipse shall prevail, that is, the clearance of the piston skirt perpendicular to the direction of the piston pin hole shall be measured. This measurement is more convenient and accurate, and in the reciprocating motion, the direction of the piston skirt perpendicular to the pin hole of the piston is greatly abraded due to the effect of lateral pressure. Therefore, when measuring the cylinder gap, the piston skirt should be perpendicular to the piston. Pin hole direction measurement.
6, avoid the piston open flame heating
Because the piston and the piston pin are in interference fit, the piston should be heated to expand when installing the piston pin. At this time, some maintenance personnel will directly heat the piston on an open flame. This is very wrong because Uneven thickness of each part of the piston, the extent of thermal expansion and contraction will not be the same, the heat of the fire will make the piston uneven heating, easily lead to deformation; the piston surface will be attached to charcoal, reducing the life of the piston. If the piston cools naturally after reaching a certain temperature, its metallurgical structure will be damaged and wear resistance will be greatly reduced, and its service life will also be significantly shortened. When installing the piston pin, the piston can be heated evenly in hot oil to make it expand slowly, and it is not allowed to directly heat with an open flame.
7, avoid grinding with abrasive cloth bearings
For some inexperienced repair engineers, the bearing bush is a difficult job. Because the scratching technology is difficult to grasp, the bearing bush is not easy to meet the technical requirements. For this reason, when replacing the bearing bush, to increase the bearing bush and the crankshaft The contact area is sanded instead of a scratch tile. This method is extremely undesirable in practical maintenance because the abrasive grains on the abrasive cloth are hard and the bearing alloy is soft, so that the sand particles can be easily embedded in the alloy during grinding and the wear of the journal can be accelerated when the diesel engine is working. Reduce the service life of the crankshaft.
8, avoid bolts tighten too tightly
During the dismantling and installation process of construction machinery, many parts of the bolts have required torque requirements, such as transmission boxes, cylinder heads, tires, connecting rods, and front axles, etc. Tightening torques are specified in the manual, and must not be specified. Feel free to change. However, many users mistakenly believe that tightening some of them will be safer, but tightening them too tightly will cause the screws or bolts to break, and it may also cause malfunctions due to threaded slides.
9, avoid the tire pressure is too high
The tire inflation pressure of wheeled construction machinery is an important factor that determines its service life and work efficiency. Tyre pressure is too high or too low will affect its service life, but also not conducive to safe driving, especially in hot summer. The scientific inflation standard should be: based on the standard tire pressure, with the temperature changes, the tire pressure slightly adjusted. For example, in summer, it should be 5%-7% lower than in winter. Taking into account the high summer temperatures, the gas is heated and the pressure is increased. In contrast, the winter must reach the standard pressure or be slightly lower.
10, avoid boiled water, add cold water
Overloading the engine, poor heat dissipation, or lack of water in the water tank can cause the tank to open. If cold water is added at once, the cylinder head and cylinder block will burst. Therefore, once the water tank is found to open in use, emergency measures shall be taken to stop the operation and allow the cooling water of the diesel engine to cool down by itself.
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