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Diesel engine maintenance and repair skills

2019-09-17
The engine is the core component of a machine, so engine maintenance and repair are critical. Let's talk about the maintenance and repair techniques of diesel engines.
First, maintenance skills
1. The "speeding" phenomenon of diesel engines and emergency measures
"Speeding" or overspeed is a phenomenon unique to the engine. When the "speeding", the speed of the diesel engine is out of control, and it is getting faster and faster, and even exceeds the maximum allowable speed with a huge sound, which seriously causes the damage of the machine to be scrapped. There are two main reasons for the "speeding": one is the failure of the fuel pump governor itself, which causes it to lose its normal adjustment characteristics; the other is the change of the speed regulation characteristics of the diesel engine, which is characterized by the fuel pump governor itself. There is no fault, and the diesel engine has additional diesel or oil entering the combustion chamber during operation. In the event of a "speeding" phenomenon, emergency measures should be taken, and a malfunction occurs when the engine speed is high to a certain extent. Emergency measures to stop speeding are:
(1) Quickly retract the accelerator pedal to the parking position.
(2) If there is a deceleration device, quickly pull the decompression handle to the oil stop position (or decompression position).
(3) Hang in the high-speed gear in time, step on the brake pedal, lift the clutch, and turn off the engine.
(4) Quickly disconnect the high pressure oil pipe and stop the oil supply.
(5) Quickly wrap the air filter with clothes to shut off the engine.
The above five steps are referred to as “deceleration, decompression, braking, and gas breaking”.
2. Inspection method for working conditions of each cylinder of diesel engine
The working conditions of each cylinder of the diesel engine can be checked by the following methods during idle operation:
(1) Listening method: Use a stethoscope or a metal rod to approach the injector body to listen to the sound of the explosion of each cylinder. The normal sound is similar to the sound of metal tapping “Dangdang”. If there is only a continuous sound of “嗬嗬”, the cylinder will supply too little oil or will not catch fire in time. For example, the knocking sound is very loud, indicating that the cylinder is too large or the injection time is too early.
(2) Color observation method: When the diesel engine is working normally, the color of the exhaust gas discharged is light gray, and the load is slightly deeper when the load is large. If black gas is discharged, it means that the combustible gas is not completely burned. Blue smoke indicates that the lubricating oil is burning into the cylinder. When the white smoke is discharged, it means that there is water in the diesel engine, and the combustible gas is not burned and white smoke is also emitted. The exhaust pipe continuously discharges abnormal smoke color, indicating that the individual cylinders are not working properly.
(3) Sensing temperature method: In the initial stage after the diesel engine is started (the exhaust pipe temperature is high after working for a period of time, the hand will burn), the temperature of each cylinder exhaust pipe can be touched by hand to identify the working condition of each cylinder. If the temperature of each cylinder exhaust pipe is higher than other cylinders, it indicates that the cylinder oil supply is high; if the temperature is low, the cylinder oil supply is small, or does not spray oil, or does not completely burn or burn after injection.
(4) Pulse method: The high pressure oil pipe is pinched by hand, and the pulsation condition when the fuel is injected is small, the pulsation is small, the sound of the explosion is weak, and the oil supply of the cylinder with low temperature is small. The outburst sound is abnormal and the temperature is high. The injector oil pressure drops, the fuel injection is poorly atomized, or it cannot be ignited and completely burned in time. The pulsation is large, the sound of the explosion is strong, and the cylinder with high temperature is the oil supply amount. The burst sound is weak and the temperature is low for the injector hole or the needle valve is stuck.
(5) Oil cut method: In order to accurately determine which cylinder is faulty, the high pressure oil pipe can be cut off from the cylinder to the injector oil circuit, that is, the work is stopped to observe the change of the working condition of the diesel engine. When the cylinder oil circuit is cut off, if the diesel engine speed and sound do not change or change little, the cylinder is working normally. If the cylinder is intermittently knocked, when the black smoke is cut off, when the oil circuit of a certain cylinder is cut off, the fault phenomenon disappears, indicating that the fault is in the cylinder.
3, diesel engine fuel economy five methods
(1) Use a fuel-saving and smoke-reducing device. The fuel-saving and smoke-reducing device is vertically fixed in the front end oil passage of the fuel injection pump, and is connected to a DC power source. Used on diesel engines, smoke reduction is significant. It not only reduces environmental pollution, but also saves about 5% of fuel.
(2) Install the inertia booster. The use of an inertial supercharger on a diesel engine generally increases power by 15% and fuel consumption by 3% to 5%.
(3) Wrap the toilet paper on the filter element. Packing 2 to 3 layers of highly absorbent toilet paper on the diesel oil filter can improve the cleanliness of the oil and reduce fuel consumption.
(4) Add foam plastic air filter. In the two-layer filter of the air filter, add a layer of 8-20mm thick foam with good air permeability to improve the filtration effect, keep the fuel burning normally and reduce fuel consumption.
(5) The return pipe is diverted. The diesel oil return pipe is connected to the high pressure oil pipe to make the oil return to the low pressure oil circuit, which can ensure normal combustion, and the fuel saving effect is very remarkable.
Second, maintenance skills
1, "three leaks" off. To repair the diesel engine, to prevent and solve the "three leaks" problem, we can adopt the "five-word" principle, that is, strict, clean, wipe, grind and tight.
Strict: The parts must be dismantled and installed in strict accordance with the operating procedures, and it is strictly forbidden to knock and knock. For example, when tightening the bolts, tighten them in order and several times. Do not twist them in order to prevent the parts from deforming.
Clean: The parts must be cleaned before assembly to prevent contamination. If the oil valve and the seat contact ring are mixed with very small debris, it will not only leak oil, but also directly affect the work of the engine.
Wipe: Apply asbestos oil to asbestos mats, paper mats, various plugs and oil spills. Make the asbestos oil thin and uniform, don't be too thick, don't smear the entire surface of the pad, just apply the oil spill.
Grinding: The joint surface of the ground or milled part, which is used to restore the surface finish and precision, so that the tubing joint or gasket can be sealed after grinding without oil leakage.
Tight: The tightness of the sealing device should be appropriate and should not be too tight or too loose. For example, various contact surfaces of the diesel engine and sealing nuts must maintain proper tightness.
2. The cylinder pressure is off. In order to ensure sufficient cylinder pressure, the clearance between the piston and the cylinder sleeve, the end and side clearance of the piston ring must meet the requirements, the sealing of the valve and the valve seat, the sealing of the front end of the injector is better, the cylinder head gasket is better, and the thickness Meet the requirements.
3. The volume of the combustion chamber is off. After the diesel engine is repaired, the volume of the combustion chamber will change, and the original compression ratio will be changed, which directly affects the normal operation of the diesel engine. The factors that change the volume of the combustion chamber include: the piston position is reversed, the cylinder gasket thickness is improper, the crank connecting rod is mechanically worn or bent, the vortex chamber insert is misaligned, and the valve sag is too large. Pay attention to these situations when repairing.
4, the timing is off. Timing off includes oil supply timing and valve timing. If the oil supply is not correct, the S195 and X195 diesel engines can be adjusted by the gasket between the fuel injection pump and the gear chamber cover, and each 0.1 mm thick gasket is added. The equivalent of the flywheel arc length is 6.3mm. If the gas is insufficient, check and correct the error on the timing gear installation, then adjust the valve clearance. The valve clearance changes by 0.1mm, the crank angle changes by 3°, which is equivalent to the flywheel arc length of 11.1mm. When compressing to the top dead center, the intake and exhaust valve clearances (cold state) should not be less than 0.2mm to prevent the components from being thermally expanded, the valve closing is not strict, or the valve head hits the piston.
5, "three filters" off. The air filter technology is not in good condition, which will cause dust to enter the cylinder and accelerate the early wear of the piston ring, cylinder, valve and valve seat, resulting in difficulty in starting and power reduction. The technical state of diesel oil and oil filter is not good, which will cause impurities to enter between the relevant parts, causing early wear of the three precision parts and accelerating the wear of the crankshaft and the bearing bush. In severe cases, the diesel engine will be scrapped early.
6, diesel atomization off. The technical state of the plunger pair, the outlet valve pair and the injector needle pair are not good, which may result in poor injection atomization, difficulty in starting the diesel engine, incomplete combustion, and increased coke, resulting in a decrease in engine power and an increase in fuel consumption. The fuel system, especially the precision parts, should be carefully checked.
7. The through hole and the small hole are closed.
(1) Through hole closing: Now take the S195 diesel engine as an example. The five through holes of the bearing and bushing should be aligned during installation.
A, the main bearing. Each pair of main bearing oil grooves is drilled with oil holes, which are respectively communicated with the oil holes on the cylinder block and the main shaft. When the flange of the main bearing is aligned with the positioning pin, the main bearing can be prevented from rotating and the oil hole is ensured. Align to make the lubricating oil road unobstructed and avoid burnout.
B. Rocker bushing. When the bushing is pressed into the rocker arm, if the hole is not aligned, the rocker arm shaft and the bushing will be burnt due to lack of lubrication and dry friction, which will increase the valve clearance and cause a severe knocking sound.
C, connecting rod bushing. The small rod of the connecting rod has an oil collecting hole, which communicates with the oil hole of the connecting rod bushing. When the copper sleeve is sleeved inside the small end of the connecting rod, if the two oil holes are not aligned, the copper sleeve and the piston pin are knocked "dang" Hit the sound and even kill.
D. Starting shaft bushing. When installing the starting shaft bushing, the two bushing oil holes should communicate with the corresponding oil collecting grooves on the body and the gear cover respectively, otherwise the starting shaft and the bushing will accelerate wear, causing the oil supply angle and the gas distribution phase to change. This causes the diesel engine power to drop.
(2) Small hole off: There are mainly 4 small holes below.
A, fuel tank cover vents. After the hole is blocked, the fuel tank is no longer open to the atmosphere, and the upper part of the oil tank will have a negative pressure due to the oil level falling, causing the oil supply to be interrupted, and the fuel will evaporate after being heated, causing the pressure in the oil tank to rise, causing oil leakage at the fuel tank switch. This hole cannot be blocked.
B, crankcase ventilation hole. After the venting hole is blocked, the exhaust gas in the crankcase accumulates more, the air pressure in the crankcase increases, the oil leaks, and the high-temperature exhaust gas mixes into the oil, which also accelerates the deterioration of the oil and accelerates the wear of the machine. Therefore, it must be repaired. To clear this hole.
C. Oil pump drain hole. The oil drain hole on the oil pump is blocked, which will cause a small amount of diesel oil leakage between the push rod and the pipe to enter the fuel injection pump, which will dilute the lubricating oil in the casing and accelerate the wear of the parts. Therefore, the hole cannot be blocked.
D. Pump drain hole. If the hole is blocked, the leaked water will not drain out of the pump body and enter the bearing housing, which will accelerate the damage of the bearing. Therefore, it is necessary to clear the hole during maintenance.
8, wear and close.
(1) Cold running. Remove the injector, use external force to drive the diesel engine, check the oil pressure and the temperature of each component, pay attention to the sound of each component, after cold running, release the oil when the temperature is high, clean the oil filter and the oil passage.

(2) Thermal running-in. No load heat running, pay attention to the working condition of diesel engine and the sound of all parts, heat-run according to the specified load and time, always pay attention to the sound of each part and the helium of the oil port, smoke exhaust, oil return to the injector, etc.

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