When repairing a diesel engine, eight key points must be strictly controlled

1. "Three leaks" off

When repairing diesel engines, to prevent and solve the "three leaks" problem, the "five-character" principle can be adopted, namely, strict, clean, wipe, grind and tight. For the disassembly and installation of parts, strict requirements must be imposed and operating procedures must be followed. Random knocking is strictly prohibited. For instance, when tightening bolts, they should be tightened in sequence and in several steps. Do not tighten them randomly without order to prevent deformation of the parts. Before assembling the components, they must be thoroughly cleaned to prevent any impurities from being mixed in. If extremely small impurities are mixed into the contact ring between the oil outlet valve and the valve seat, it will not only cause oil leakage but also directly affect the operation of the engine. Apply asbestos oil to the leakage points of asbestos gaskets, paper gaskets and various screw plugs. When applying asbestos oil, do it thinly and evenly. Do not apply it too thickly, nor cover the entire surface of the pad. Only apply it to the leaking area. Grinding: The mating surface of parts is ground or milled. Its function is to restore the surface's smoothness and precision, so that the oil pipe joint or gasket can maintain a seal and not leak oil after grinding. Tightness: The tightness of the sealing device should be appropriate, neither too tight nor too loose. For instance, various contact surfaces and sealing nuts of diesel engines must maintain an appropriate tightness.

2. Cylinder pressure off

To ensure sufficient cylinder pressure, the fit clearance between the piston and the cylinder liner, the end and side clearances of the piston rings must meet the requirements. The sealing performance of the valves and valve seats, as well as the sealing performance at the front end of the fuel injector, should be good. The cylinder gasket should be in good condition and its thickness should meet the requirements.

3. The volume of the combustion chamber is related

After a diesel engine is repaired, the combustion chamber volume often changes, altering the original compression ratio and directly affecting the normal operation of the diesel engine. The factors that cause changes in the combustion chamber volume include: incorrect piston position installation, improper cylinder gasket thickness, mechanical wear or bending of the crankshaft connecting rod, misalignment of the vortex chamber insert, and excessive valve depression, etc. During repair, these situations should be paid attention to.

4. Timing off

Timing control includes fuel supply timing and valve timing. If the fuel supply is not timed, the S195 and X195 diesel engines can be adjusted by means of the gasket between the fuel injection pump and the gear housing cover. For every 0.1mm thick gasket added or removed, it is equivalent to a flywheel arc length of 6.3mm. When the air supply is insufficient, the installation error of the timing gear should be checked and corrected first, and then the valve clearance should be adjusted. For every 0.1mm change in the valve clearance, the crankshaft Angle changes by 3 degrees, which is equivalent to a flywheel arc length of 11.1mm. During adjustment, it should be noted that when the piston is compressed to the top dead center, the intake and exhaust valve clearances (in cold running state) should not be less than 0.2mm to prevent the components from expanding due to heat. The valve does not close tightly, or the valve head hits the piston.

5. "Three filters" stage

Poor technical condition of the air filter will allow dust to enter the valves. Accelerate the early wear of piston rings, cylinders, valves and valve seats, causing difficulties in starting and a decrease in power. Poor technical conditions of diesel and oil filters can allow impurities to enter between related components, causing premature wear of the three precision pairs, accelerating the wear of the crankshaft and bearing shells, and in severe cases, leading to the early scrapping of the diesel engine.

6. Diesel atomization off

Poor technical conditions of the plunger pair, fuel outlet valve pair and injector needle valve pair can all lead to poor atomization of fuel injection, making it difficult to start the diesel engine, incomplete combustion, increased carbon deposits, resulting in a decrease in engine power and an increase in fuel consumption. Therefore, the fuel system, especially the precision mating parts, should be carefully inspected.

7. Through holes and small holes are closed

(1) Regarding the through holes, taking the S195 diesel engine as an example, the five through holes of the bearing and bushing must be aligned during installation.

A. Main bearings: Each pair of main bearings has oil holes drilled in the oil grooves, which are respectively connected to the oil on the cylinder block and the main journal. During installation, as long as the flange notches of the main bearings are aligned with the locating pins, it can prevent the main bearings from rotating, ensure that the oil holes are aligned, and keep the lubricating oil passage unobstructed to avoid burning out.

B. Rocker arm bushing. When the bushing is pressed into the rocker arm, if the holes are not aligned, the rocker arm shaft and the bushing will be burned out due to lack of lubrication and dry friction, causing the valve clearance to increase and generating a serious knocking sound.

C. Connecting rod bushings. The small end of the connecting rod is drilled with an oil collection hole, which is connected to the oil hole of the connecting rod bushing. When a copper sleeve is inserted into the small end of the connecting rod, if the two oil holes are not aligned, the copper sleeve and the piston pin will make a "ding-dong" knocking sound, or even seize.

D. Starting shaft bushings: When installing the starting shaft bushings, the oil holes of the two bushings should be respectively connected to the corresponding oil collection grooves on the engine block and the gear cover. Otherwise, the starting shaft and the bushings will wear out faster, causing changes in the fuel supply Angle and valve timing phase, and resulting in a decrease in the power of the diesel engine.

(2) The main small holes of the fuel tank cap are as follows: A. Vent hole of the fuel tank cap. After the hole is blocked, the fuel tank is no longer connected to the atmosphere. Due to the drop in the oil level at the top of the fuel tank, negative pressure will occur, causing the fuel supply to be interrupted. When the fuel is heated and evaporates, the pressure inside the fuel tank rises, which may cause oil leakage at the fuel tank switch. Therefore, this hole must not be blocked.

B. Crankcase vent hole: Once the vent hole is blocked, more and more exhaust gas will accumulate inside the crankcase, causing the air pressure inside the crankcase to rise. This will lead to oil leakage, and the high-humidity exhaust gas will mix into the oil, accelerating the deterioration of the oil and the wear of components. Therefore, it is essential to clear this hole during maintenance.

C. Oil drain hole of the oil transfer pump. If the oil drain hole on the fuel transfer pump is blocked, a small amount of diesel will seep into the fuel injection pump between the push rod and the guide pipe, diluting the lubricating oil in the housing and accelerating the wear of the parts. Therefore, this hole must not be blocked either.

D. The drainage hole of the water pump. If this hole is blocked, the leaked water cannot be discharged from the pump body and enters the bearing housing, which will accelerate the damage of the bearing. Therefore, during maintenance, it is essential to clear this hole.

8. Running-in stage

Cold running-in. Remove the fuel injector, drive the diesel engine to run with external force, and at the same time check the oil pressure and the temperature of each part. Pay attention to listening to the sounds of each component. After cold running-in, when the temperature is high, drain the oil and clean the oil filter and oil passage.

(2) Hot running-in. No-load hot running-in, pay attention to the working condition of the diesel engine and the noise of each part. Heat run-in according to the specified load and time. Always pay attention to the sounds from all parts, as well as the air leakage from the oil port, smoke exhaust, and oil return from the fuel injector. Any problems found should be promptly eliminated.