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Adjustment and repair of fuel injection pump for diesel engine

- Aug 13, 2018 -

Adjustment and repair of fuel injection pump for diesel engine


The fuel injection pump is an important part of the diesel fuel supply system, which is regarded as the "heart" of the diesel engine, and once it is out of problems it will make the whole diesel engine work out of the wrong way.


The uneven fuel supply of the injection pump will lead to black smoke, unstable speed and insufficient power in the exhaust pipe, thus affecting the reliability and economy of the engine.



Cause of uneven oil supply in fuel injection pump


The failure of 

1. parts caused the inhomogeneous supply of oil. After long term use, the driving gear wear and the backlash increase because the fuel injection pump drives the loose shaft and the gap is too large. It will also affect the oil supply uniformity. High pressure oil pipe joint because of frequent vibration or tightened leakage, as well as tightening force over the joint metal off and blocking the tubing, also can cause uneven oil supply of each cylinder. In addition, in the fuel injection pump and governor spring, the plunger spring has higher breaking frequency because of its large deformation, strong force and high working frequency, so the light injection amount is reduced, the injection quantity of each cylinder is uneven, the interval time of each cylinder is too bad, the beginning time of the injection is delayed, and the heavy oil supply is discontinuous or even can not supply oil.



2. the oil supply is not uniform when debugging. When the fuel injection pump is debugged on the test bench, it is required that the fuel supply unevenness of each cylinder at rated speed should be less than 3%. In the actual debugging process, because the length, shape and caliber of the special injector and high pressure oil pipe of the test rig are not identical with the original machine, and the difference of the debugging technology is added, the oil quantity inhomogeneity in the actual jetting pump is often greater than 3% after the injection pump is installed.



Adjustment method of non uniform oil supply for fuel injection pump


1. After the fuel injection pump is installed, the fuel supply time is adjusted according to the prescribed standard, and the exhaust manifold is unloaded to observe the working condition of each cylinder.


2. start the diesel engine, the idle speed of 2 to 3min, touch each cylinder exhaust port and the cylinder head near the injector. If the temperature of a certain cylinder is too high, it can be preliminarily determined that the oil supply of the cylinder is much less.


3. When the engine temperature is over 50 degrees Celsius, let the engine run at rated speed, at the same time check the smoke color of the exhaust port, pay attention to the sound of the cylinder. If there is a black smoke in a certain cylinder, it shows that the supply of oil is too large


4. check the oil supply advance angle. In general, the oil spill method can be used to check the oil supply advance angle. The joint of the high pressure tubing of one end of the oil pump is loosened, the joint of one end of the fuel injector is removed, the oil pipe is turned to the horizontal position, then the high-pressure oil pipe joint of the oil pump is tightened, the throttle is pulled to the maximum position and the pressure reducer is opened until several drops of the high-pressure oil pipe exit. So far as diesel.


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How do the injection time of the fuel injection pump be incorrect?


The fuel injection time of the fuel injection pump is the starting time (expressed by the crankshaft rotation angle) when the engine is running and the nozzle injects fuel into the cylinder. After the diesel engine is injected into the cylinder, it is mixed with the air into a combustible mixture to ensure that the combustible mixture is fully burned and the combustion pressure is maximum at some time after the top stop to ensure the normal operation of the diesel engine. The injector must start at some point before the compression stop. The engine has different injection start time under different load and speed. The injection start time corresponding to the calibrated load is called the calibrated injection time. In use, it is reasonable to check the fuel injection time at the demarcated load, but due to the limitations of conditions and equipment, the fuel injection time should be checked instead. The oil supply time of the injection pump refers to the moment when the hand throttle is in the maximum position, rocking the crankshaft to drive the plunger pump oil, and when the oil valve is opened at the top of the oil hole (expressed in the crankshaft corner).


1. The incorrect performance of the fuel injection time of the injection pump


The symptoms manifested by premature or late fuel supply of a diesel engine are the same: inability to work, difficult start-up, exhaust smoke, and excessive temperature. But each has its own characteristics. According to their different appearance characteristics, it can be judged whether the advance angle of oil supply is too big or too small.


The oil supply time is too early, the crankshaft is easy to reverse, the diesel engine works rough, the sound of the cylinder knocks, the sound of the knocking sounds like the sound made when the hardwood hammer knocks the piston, the sound of the sound is more obvious at the low speed, the more the oil supply angle is bigger, the clearer the percussion sound in the cylinder is. If the sudden increase of the throttle knock increases, quickly reduce the throttle sound disappears, the speed decreases and the sound appears again. The diesel engine runs well at high speed, deteriorates when it drops to low speed and emits black smoke intermittently from the exhaust pipe. According to such symptoms, it can be preliminarily concluded that the oil supply time is too early.


When the fuel supply time is too late, the diesel engine is easy to overheat, the water temperature rises faster, and the cooling water is easy to boil. For example, the performance of diesel engine in low speed is good, the work deteriorates after the speed is raised, the exhaust pipe is intermittent smoke, and the white smoke has a rough "Peng, bulging" sound, and the speed of the engine diesel engine increases slowly. But smoke and noise are more obvious. According to such symptoms, it can be preliminarily concluded that the supply time is too late.


2. The necessity of adjusting the time of oil supply


During the use, the oil supply time will change because of the wear of the parts or the change of the relative position. When it exceeds a certain range, the performance of the diesel engine will be deteriorated and the work is not normal. In addition, the engine cylinder, piston wear or crankshaft and connecting rod will also deviate from the injection time required by the normal combustion (plunger pair, the wear of the oil outlet valve, the change of the oil supply time, and the replacement of the new parts). Therefore, the fuel injection time of the engine in use should be adjusted regularly.



3. Adjustment method


We take 4125A4 diesel engine fuel injection pump as an example to illustrate the adjustment of fuel supply time. The fuel injection pump of 4125A4 diesel engine uses a disc to adjust the fuel supply time of the fuel injection pump. The disc adjusting mechanism is also a connecting device between the camshaft of the fuel injection pump and the timing gear, which is fixed by two bolts. In the adjustment device, there are 14 holes in the front end face of the timing gear (pointing to the direction of the tractor) and the flower tray (the screw holes on the end of the timing gear and the through holes on the disc), which are divided into two groups (each of the 7 holes is a group). The radial position of the two sets of holes is the same (two groups of holes are in the same circle diameter). The screw holes on the face of the timing gear are not grouped and changed to 16 holes, and the angle of each two holes is 22.5 degrees, and the disc is still 14 holes. The gears were divided into two groups with 16 holes distributed evenly on the end face of timing gears with an angle of 21 degrees between holes. Some tractors can solve the problem of adjusting the time of oil supply because of the long time of use and the serious wear of the driving mechanism of the injection pump. The time adjustment of the oil supply can be solved without timing gear error (near the mark teeth of the timing gear or the tooth meshing of the wrong front), and the 3 degree change of the time of the stepless adjustment of oil supply can be realized.


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During the inspection adjustment, if the 4 hole is fixed to the 4 hole and the oil supply time is too late, the two fixed bolts should be moved in clockwise direction to the other corresponding hole positions (for example, the 5 hole of the flower plate to the corresponding screw hole of the timing gear face). When adjusting, the fixed bolt is screwed out, clockwise (to adjust the time of oil supply in advance) or counter clockwise (for oil supply time later adjusted) inserted into the same direction, the same hole position of Kong Zhong (for example: the flower plate is in the 4 hole before adjustment, adjust to the 6 hole position in advance; the timing gear is also to be adjusted before the adjustment. " The hole is moving two holes in the direction of clockwise. When adjusting the oil supply time, the fixed bolt inserted into the variable hole position can not be corrected because the angle between the disc and the end face of the timing gear is not equal. From the structure analysis, the angle between the holes of the disc is small (21 degrees), the angle between the timing holes of the timing gear is large (22.5 degrees). If the fixed bolt is changed in the direction of clockwise, it is necessary to rotate the disc in clockwise direction in order to make the two holes correct when the timing gear is not moving. If the disc does not move, the timing gear must be turned counterclockwise. Similarly, when the fixed bolt changes counter-clockwise, it must rotate the disc counter-clockwise or the timing gear clockwise to align the positive hole position. When the fixed bolt moves clockwise, rotating the disc clockwise to make the hole position correct, the essence of the problem is to move the oil supply starting point of the injection pump camshaft to the front of the top of the compression point. The reverse clockwise rotation of the timing gear is the essence of the anti roll crankshaft (driven by a small starter), and the injection pump camshaft oil supply starting point is fixed at the front of the compression point. The fixed bolt is moving in the direction of clockwise. The quality problem is also the position of the oil supply starting point of the injection pump camshaft, which is close to the compress stop point, so that the time of oil supply is postponed.


Therefore, it is necessary to clear two points when adjusting the time of oil supply with the structure of the flower plate: 

(1) the fixed bolt moves clockwise, the time of oil supply is ahead of time; the time is moved against clockwise direction and the time of oil supply is later later. When the fixing bolt moves, it must be screwed out of the original installation hole and inserted into the corresponding hole of the flower plate and the timing gear in the same direction and the same number of moving holes. (2) When the bolt is moved to the new hole position, the cam or crankshaft can be rotated to make the disc and the timing gear align in the same hole position. But it must be noted that the direction of the two turns is opposite. When adjusting properly, it is necessary to tighten and lock the fixed bolt of the disc and timing gear.


S195 diesel engine uses gaskets between the mounting surfaces of the pump body to adjust the fuel supply advance angle. The oil supply advance angle decreases with the increase of gaskets and increases with the decrease of gaskets.


Maintain


Injection pump is one of the most important components of diesel engine, its quality will directly affect the power, economy and reliability of the engine. So how should the injection pump be maintained?


1. Use good diesel and filter. Because of the special working mode of diesel engine, the requirement of diesel filter is much higher than that of gasoline engine. Therefore, it is necessary to strengthen the cleaning and maintenance of diesel filter, timely cleaning or replacement of filter elements.


2. Check the quantity and quality of oil in the oil pool of fuel injection pump. If the oil is mixed or inadequate, the light causes the wear of the plunger and the oil valve, which leads to the lack of power, the difficulty of starting, and the corrosion rust of the plunger and the oil valve.


3. Check the advance angle of fuel supply and the interval angle of each cylinder regularly. If the fuel supply advance angle of the injection pump changes, the power and economy of the diesel engine will be worse, the start-up will be difficult, the operation will be unstable, and the engine will emit abnormal sound.


4. Regularly check and adjust the fuel supply of each cylinder of the injection pump. If the fuel injection quantity of each cylinder is not uniform, it will lead to difficult start-up, insufficient power, increased fuel consumption and unstable operation of the diesel engine.


5, check the camshaft clearance regularly. The oversize of the camshaft will increase the impact of the cam surface and change the advance angle of the oil supply, so the camshaft clearance should be checked regularly to keep it between 0.03~0.15mm.


6. Use the standard high pressure oil pipe. As the diesel engine works by the mode of compression ignition, the fuel supply pressure is much larger than that of the gasoline engine, so the standard high pressure oil pipe is needed to ensure the uniform oil supply interval angle and the uniform supply of the oil.


7. Check the wear and tear of the key slot and fixing bolt regularly. For example, the camshaft keyway, the semicircle key, the fuel injection pump camshaft keyway and so on.


8. Replace the worn plunger and the oil outlet valve coupling in time. When the diesel engine is difficult to start, the power decline, and the fuel consumption increases, it should be checked if the wear of the plunger and the oil valve is caused by the wear and tear. If it is, it should be changed in time. This will make the diesel engine's power and economy significantly improved.