Engine oil only
Motor oil is indispensable in the use of diesel engines, and mainly plays the role of lubrication, cooling and cleaning.
Therefore, many drivers will pay attention to check the amount of lubricating oil and add it according to the standard, but they ignore the inspection of the quality of the lubricating oil and the replacement of the deteriorated oil, resulting in the moving parts of some engines always in poor lubrication Operating in the environment, thereby accelerating the wear of various parts.
Under normal circumstances, the loss of engine oil is not great, but it is easily contaminated, thereby losing the role of protecting the diesel engine. During the operation of a diesel engine, many pollutants (soot, soot, and fouling from incomplete combustion of fuel) will enter the engine oil.
For new or overhauled machinery, there will be more impurities after trial operation. If it is rushed to use only if it is not replaced, it may easily cause accidents such as burning of the tile and holding the shaft.
In addition, even if the engine oil is changed, some drivers will not thoroughly clean the oil passage during the replacement due to lack of maintenance experience or save trouble, so that mechanical impurities still remain in the oil pan and the oil circuit.
2. Random use of butter
Cylinder pads are buttered. Butter is a commonly used grease in the repair of construction machinery, which can play a role of lubrication and sealing.
Therefore, some repairmen will apply a layer of butter to the cylinder gasket when installing the cylinder gasket, which is believed to increase the tightness of the diesel engine. As everyone knows, this will actually affect the working performance of the diesel engine.
Cylinder gasket is an important seal between the cylinder block and the cylinder head of the diesel engine. It can not only seal the high temperature and high pressure gas generated in the cylinder, but also the cooling water and lubricating oil in the cylinder head and the cylinder. When installing the cylinder gasket, pay special attention to its sealing quality.
If grease is applied to the cylinder pad during installation, when the cylinder head bolts are tightened, a part of the butter will be squeezed into the cylinder water passage and oil passage. The butter left between the cylinder pads will be affected by the high temperature during the work of the cylinder, and some of it 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 head, the cylinder head and the plane of the body. High-temperature and high-pressure gas can easily hit the cylinder head from here, destroy the cylinder head, and cause leakage. gas.
In addition, when the butter is in a high temperature for a long time, it will also cause carbon deposits, which will cause premature aging and deterioration of the cylinder liner. Therefore, do not apply butter when installing the cylinder gasket.
3.Cylinder liner and piston are installed without option
When replacing cylinder liners and pistons, the new cylinder liners and pistons are considered standard parts and are interchangeable, so they can be used after being installed.
In fact, the dimensions of the cylinder liner and the piston have a certain tolerance range.
For example, if a large-sized cylinder sleeve is matched with a small-sized piston, the fit clearance will be too large, resulting in weak compression and difficulty in starting.
Therefore, the size group code of the standard cylinder liner and piston must be checked during the replacement. The size group code of the standard piston and the piston must be the same as the size group code of the standard cylinder liner. Only in this way can the two be guaranteed. With standard fit clearance.
In addition, when the cylinders and pistons of the same group code are installed in each cylinder, pay attention to the inspection of the cylinder plug clearance before installation. In order to ensure the assembly standard, a test should be performed before installation to prevent fake and inferior products from being installed. .
4. Cylinder gap measurement is inaccurate
When measuring the cylinder clearance, the piston skirt was not measured in a direction perpendicular to the piston pin hole, and was measured in other directions.
The structural characteristics of the aluminum alloy piston are that the upper part is smaller and the lower part is a cone, and the cross section of the skirt is oval, so the cylinder gaps in the circumferential direction are not equal.
During the measurement, the clearance in the direction of the major axis of the ellipse shall prevail, that is, the clearance between the piston skirt and 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 piston pin hole is subject to greater wear due to the lateral pressure. Therefore, when measuring the cylinder clearance, the piston skirt should be perpendicular to the piston. Measure the direction of the pin hole.
5.Piston flame heating
Because the piston and the piston pin are in an interference fit, when installing the piston pin, the piston should be heated to expand first. At this time, some maintenance personnel will directly place the piston on an open flame to heat it.
This method is very wrong, because the thickness of each part of the piston is uneven, the degree of thermal expansion and contraction will be different, the heating of the open flame will cause the piston to be unevenly heated, and easily cause deformation; carbon ash will also adhere to the surface of the piston, reducing the Service life.
If the piston naturally cools after reaching a certain temperature, its metallographic structure will be damaged and the wear resistance will be greatly reduced, and its service life will be significantly shortened.
When installing the piston pin, the piston can be evenly heated in hot oil to make it expand slowly. Do not directly heat it with an open flame.
6. Polish the bearing pad with emery cloth
For some inexperienced repairmen, scraping the shoes is a difficult task. Because the scraping technology is difficult to master, it is difficult for the bearing to meet the technical requirements.
For this reason, when replacing the bearing bush, in order to increase the contact area between the bearing bush and the crankshaft, it is polished with abrasive cloth instead of scraping the bush.
This method is extremely undesirable in actual maintenance, because the abrasive particles on the abrasive cloth are harder, but the bearing alloy is softer. In this way, the abrasive particles are easily embedded in the alloy during grinding, and the journal wear will be accelerated when the diesel engine works Reduce the life of the crankshaft.
7. The bolt is too tight
During the disassembly and assembly of construction machinery, many parts of the bolts have specified torque requirements, such as transmission boxes, cylinder heads, hubs, connecting rods, and front axles. The tightening torques are specified in the instructions. Feel free to change.
However, many users mistakenly believe that it is safer to tighten tightly, but tightening too tightly may cause the screws or bolts to break, and may also cause failure due to threaded sliding buckles.
8. 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.
Too high or low tire pressure will affect its service life, and it is also not conducive to safe driving, especially in the hot summer.
The scientific inflation standard should be: take the tire's standard air pressure as a benchmark, and as the temperature changes, slightly adjust the tire air pressure.
For example: summer should be 5% to 7% lower than winter. Considering that the summer temperature is high, the gas is heated, and the pressure is increased, on the contrary, it must reach the standard pressure or a little lower in winter.
9. Do not check the plunger stroke margin
In the irony of the plunger fuel injection pump, many maintenance personnel did not pay attention to check the plunger stroke margin.
The stroke allowance of the plunger refers to the amount of movement that the plunger can continue to move upward after being pushed by the cam on the camshaft to the top dead center.
After adjusting the oil supply start time, the reason for checking the stroke margin is because the stroke margin of the plunger is related to the wear of the plunger and the sleeve.
After the plunger and the sleeve are worn, the plunger needs to move up a little more to start the oil supply, which delays the start of the oil supply. When the adjustment bolt is unscrewed or replaced with a thicker adjustment block or washer, the plunger's low position is moved up, so that the stroke allowance of the plunger is reduced.
Therefore, when repairing and debugging the fuel injection pump, the stroke margin should be checked first to determine whether the fuel injection pump can still be adjusted.
During the inspection, the following different methods should be adopted according to the different structures of the fuel injection pump:
a) After turning the camshaft and pushing the plunger to the top dead center, remove the oil outlet valve and valve seat and measure with a depth vernier.
b) After the plunger is pushed to the top dead center, use a screwdriver to pry up the spring seat of the plunger spring to raise the plunger to a high point.
Then use a thick gauge to measure between the lower plane of the plunger and the tappet adjustment bolt. The standard stroke allowance of the plunger is about 1.5mm, and the limit stroke allowance after wear should not be less than 0.5mm.
10. Add cold water to the water tank
Engine overload operation, poor heat dissipation, or lack of water in the water tank will cause the water tank to open. At this time, if cold water is added immediately, the cylinder head and cylinder body will burst.
Therefore, once the water tank is found to be in use during the use, emergency measures should be taken to stop the operation to cool the cooling water of the diesel engine by itself.