1.Only add engine oil without changing it

Oil is essential in the use of diesel engines, mainly for lubrication, cooling, cleaning, and other functions.

Therefore, many drivers pay attention to checking the amount of lubricating oil and adding it according to standards, but neglect the inspection of lubricating oil quality and the replacement of deteriorated oil, resulting in some engine moving parts always operating in poor lubrication environments, thereby accelerating the wear of various parts.

Under normal circumstances, the loss of engine oil is not significant, but it is prone to pollution and thus loses its protective effect on diesel engines. During the operation of a diesel engine, many pollutants (such as soot, carbon deposits, and scale generated by incomplete combustion of fuel) will enter the engine oil.

For new or overhauled machinery, after trial operation, there will be more impurities. If only adding or not replacing it is urgent to put it into use, it is easy to cause accidents such as tile burning and shaft sticking.

In addition, even if the engine oil is changed, some drivers may not thoroughly clean the oil ducts during the replacement due to lack of maintenance experience or trouble saving, resulting in mechanical impurities still remaining in the oil pan and oil circuit.

2.Misuse and spread of butter

Apply grease to the cylinder gasket. Butter is a commonly used lubricating grease in engineering machinery repair, which can play a role in lubrication and sealing.

Therefore, some repairmen apply a layer of butter to the cylinder gasket when installing it, believing that this can increase the sealing of the diesel engine. Little did they know that doing so actually affected the working performance of the diesel engine.

Cylinder gasket is an important sealing component between the cylinder block and cylinder head of a diesel engine. It not only seals the high-temperature and high-pressure gases generated in the cylinder, but also seals the cooling water and lubricating oil in the cylinder head and cylinder body. Therefore, when disassembling cylinder gaskets, special attention should be paid to their sealing quality.

If butter is applied to the cylinder gasket during installation, when the cylinder head bolts are tightened, a portion of the butter will be squeezed into the cylinder water and oil channels. The butter left between the cylinder gaskets during cylinder operation will flow into the cylinder for combustion due to the influence of high temperature, while the remaining part will remain on the joint surface of the cylinder block and cylinder head, creating gaps between the cylinder gasket, cylinder head, and the plane of the cylinder body. High temperature and high pressure gas can easily impact the cylinder gasket from here, Damaging the cylinder gasket, causing air leakage.

In addition, prolonged exposure to high temperatures in butter can also cause carbon buildup, leading to premature aging and deterioration of the cylinder gasket. Therefore, do not apply butter when installing the cylinder gasket.

3.New cylinder liners and pistons can be installed without selection

When replacing the cylinder liner and piston, it is believed that the new cylinder liner and piston are both standard parts with interchangeability, and can be used once installed.

In fact, there is a certain tolerance range for the dimensions of the cylinder liner and piston.

If a large-sized cylinder sleeve is matched with a small-sized piston, it will cause excessive fit clearance, resulting in weak compression and difficulty in starting.

Therefore, when replacing, it is necessary to check the size grouping code of the standard cylinder liner and piston. The installed cylinder liner and piston must have the same size grouping code as the standard cylinder liner, in order to ensure a standard fit gap between the two.

In addition, when installing cylinder liners and pistons with the same grouping code for each cylinder, attention should also be paid to checking the gap between the cylinder plugs before installation. In order to ensure assembly standards, a test should also be conducted before installation to prevent the installation of counterfeit and defective products.

4.The measurement of cylinder clearance is not accurate

When measuring the cylinder clearance, it was not measured in the direction perpendicular to the piston pin hole on the piston skirt, but in other directions.

The structural characteristics of aluminum alloy pistons are that they are small at the top and large at the bottom, forming a cone, and the cross-section of the skirt is elliptical, so the cylinder clearances along the circumference are not equal.

When measuring, it is stipulated that the clearance in the direction of the long axis of the ellipse shall prevail, that is, the clearance measured from the piston skirt perpendicular to the piston pin hole direction.

This measurement is more convenient and accurate, and during reciprocating motion, the direction of the piston skirt perpendicular to the piston pin hole is subject to greater wear due to lateral pressure. Therefore, when measuring cylinder clearance, it is recommended to measure in the direction of the piston skirt perpendicular to the piston pin hole.

5.Open fire heating of piston

Due to the interference fit between the piston and the piston pin, the piston should be heated and expanded before installing the piston pin. At this point, some maintenance personnel will place the piston directly on an open flame for heating.

This practice is very wrong because the thickness of each part of the piston is uneven, resulting in different degrees of thermal expansion and contraction. Heating with an open flame will unevenly heat the piston, which can easily cause deformation; The surface of the piston will also adhere to the charcoal ash, reducing the service life of the piston.

If the piston cools naturally after reaching a certain temperature, its metallurgical structure will be damaged and its wear resistance will be greatly reduced, and its service life will also be significantly shortened.

When installing the piston pin, the piston can be evenly heated in hot oil to slowly expand it, and it is not necessary to directly heat it with an open flame.

6.Polish the bearing bush with emery cloth

For some inexperienced repair workers, scraping the bearing bush is a difficult task. Because the scraping technique is difficult to master, it is difficult to meet the technical requirements for the bearing bush.

Therefore, when replacing the bearing bush, some people use emery cloth to polish instead of scraping to increase the contact area between the bearing bush and the crankshaft.

This method is not recommended in actual maintenance because the abrasive particles on the abrasive cloth are relatively hard, while the bearing alloy is relatively soft. This can easily cause the abrasive particles to embed into the alloy during polishing, accelerating the wear of the journal and shortening the service life of the crankshaft during operation of the diesel engine.

7.The bolt is too tight

During the disassembly and assembly process of construction machinery, there are specified torque requirements for many parts of the bolts, such as the transmission case, cylinder cover, hub, connecting rod, and front axle. The tightening torque is specifically specified in the instructions and must not be arbitrarily changed.

However, many users mistakenly believe that tightening the screw will be safer, but too tight tightening can cause the screw or bolt to break, or may cause failure due to thread slipping.

8.The tire pressure is too high

The inflation pressure of the tires of wheeled construction machinery is an important factor in determining its service life and work efficiency.

Too high or too low tire pressure will affect its service life and is not conducive to safe driving, especially in the hot summer.

A scientific inflation standard should be based on the standard pressure of the tires, with slight adjustments to the tire pressure as the temperature changes.

For example, the pressure in summer should be 5 %-7 % lower than that in winter, considering the high temperature and the increase in pressure due to heating of the gas. Conversely, the pressure in winter must reach the standard or slightly lower.

9.Do not check the plunger stroke allowance

In the mocking test of the plunger fuel injection pump, many maintenance personnel did not pay attention to checking the stroke allowance of the plunger.

The so-called stroke allowance of the plunger refers to the amount of movement that the plunger can continue to move up after being pushed up to the top dead center by the cam on the camshaft.

After adjusting the start time of fuel supply, the reason for checking the stroke allowance is because the stroke allowance of the plunger is related to the wear of the plunger and sleeve.

After the plunger and sleeve are worn, the plunger needs to move upwards for an additional period of time to start supplying oil, thereby delaying the start time of supplying oil. After screwing out the adjustment bolt or replacing it with a thicker adjustment pad or gasket, the lower position of the plunger moves up, reducing the stroke margin of the plunger.

So, when repairing and debugging the fuel injection pump, * the stroke margin should be checked first to determine whether the fuel injection pump still allows adjustment.

When checking, the following different methods should be used based on the different structures of the fuel injection pump:

a) Rotate the camshaft, push 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, causing the plunger to rise to the high point.

Then insert a thickness gauge between the lower plane of the plunger and the adjusting bolt of the tappet to measure. The standard stroke allowance of the plunger is about 1.5mm, and the wear limit stroke allowance should not be less than 0.5mm.

10.Quickly add cold water when the water tank is boiling

Overloading the engine, poor heat dissipation, or a shortage of water in the water tank can cause the water tank to boil. If cold water is added immediately at this time, it can cause the cylinder head and cylinder block to burst.

Therefore, once the water tank is found to be boiling during use, emergency measures should be taken to stop the operation and allow the diesel engine cooling water to cool down on its own.