Inspection and Replacement of Diesel Fuel Injection Pump Couple

by MOU YONG HONG on December 02, 2021

Abstract: The technical status of diesel fuel injection pump couples directly affects the performance of diesel engines. This article introduces the inspection method of the technical status of the fuel injection pump coupler and focuses on how to ensure the assembly quality of the plunger coupler and the fuel outlet valve coupler when the fuel injection pump is assembled.

The fuel injection pump is also called a high-pressure fuel pump. Its function is to increase the pressure of the diesel fuel sent by the fuel delivery pump and supply fuel to each fuel injector regularly and quantitatively. The important components of the fuel injection pump are the plunger assembly and the fuel outlet valve assembly, and the injector needle valve assembly is called the three most important precision fittings of the diesel engine fuel system. The integrity of the technical status of the plunger couple and the outlet valve couple directly affects the quality of the fuel injection pump and has a great impact on the performance of the diesel engine.

 1 Technical inspection of the fuel injection pump

1.1 Plunger

Plunger and plunger sleeves are collectively called plunger couples, which are the key parts for high pressure generated by the fuel injection pump. When the fuel injection pump works, the plunger reciprocates up and down in the plunger sleeve to complete the pumping process of oil suction, pumping oil, and returning oil. The main reason for the failure of the plunger couple is wearing. The area of ​​the plunger facing the oil inlet is the most severely worn. If the surface has scratches along the axis and the scratches are widely distributed, when the wear area is milky white, new parts should be replaced. When the plunger stops supplying, the edges and edges are straight and blunt, and when the irregular collapse occurs, it cannot be used any longer, and new parts need to be replaced. In addition, the tightness test of the plunger pair should also be carried out. The test is carried out on special instruments. If there is no special instrument, the high-pressure fuel pipe joint of the fuel injection pump can also be blocked by a non-through hole nut, and then the fuel pump tappet is continuously pried with a crowbar to keep the diesel on the top of the plunger in compression. If after a period of prying pressure, the tappet can no longer continue to move up and down, indicating that the plunger pair has good tightness performance. If you can always pry the tappet up and down, it means that the tightness of the plunger pair has been destroyed and can no longer be used. It should be replaced. When the plunger pair is replaced, the whole set should be replaced.

1.2 Oil valve assembly

The outlet valve couple is also one of the important couplers on the fuel injection pump. After long-term use of the outlet valve coupler, due to the force of the outlet valve spring, the residual pressure of the fuel in the fuel pipe and the effect of mechanical impurities, the sealing cone surface of the outlet valve coupler and the sealing ring of the pressure relief ring is often poor, resulting in The pressure-reducing effect is reduced, the fuel in the high-pressure fuel pipe leaks back, afterburning of the diesel engine, the fuel injector is not twelve brittle, and the cylinder knocks at high speed.

At present, there are several methods commonly used for testing the tightness of the oil outlet valve coupler, such as the direct observation method, the sealing performance test method, and the mechanical inspection. There are obvious signs of external wear to be replaced. The seal test is generally performed by using the fuel pressure of the fuel injection tester before the fuel injection pump is disassembled or after it is installed.

2 Points for attention when replacing the fuel injection pump

Ensuring the assembly quality of the plunger and the fuel outlet valve assembly is an important part of ensuring the maintenance quality of the fuel injection pump, and thus ensuring the power, economy, and reliability of the diesel engine. Pay attention to the following items when correctly assembling the plunger and the oil outlet valve assembly:

(1) Before and during assembly, carefully clean the plunger and the oil outlet valve assembly, the injection pump plunger sleeve mounting seat hole, the oil outlet valve seat, and the oil outlet valve sealing gasket.

(2) The support shoulder of the mounting seat hole of the plunger sleeve should be smooth and free of deformation, scratches, and cracks. The seat hole is squeezed by the shoulder of the plunger sleeve to cause local shrinkage deformation, which causes stress to the plunger sleeve, causing the plunger to move up and down, left and right rotation blocked, or even stuck. At this time, an adjustable hand reamer should be used to hinge it to the standard size.

(3) The sealing gasket between the shoulder of the plunger sleeve and the supporting shoulder of the mounting seat hole of the plunger sleeve should be intact, and the thickness of each sealing washer should be the same.

(4) After the positioning screw of the plunger sleeve is tightened, the plunger sleeve should move slightly axially in the seat hole, and there should be no rotation around the axis. Set screw sealing washer should be intact to ensure sealing. At the same time, we must pay attention to the thickness of the washer and the length of the screw. In any case, the screw should not be pressed against the plunger sleeve, and the plunger sleeve should not be blocked into the oil return hole.

(5) The plunger tail moves axially in the plunger spring seat, generally 0.25 ~ 0.55 mm. When it does not match, it can be adjusted by changing the relative position of the adjusting arm axial. When the bearing surface of the tappet body adjustment screw is badly worn, the adjustment screw can be repaired or replaced separately. If the clearance is too small, do not grind the end of the plunger, because it not only affects the surface shape and position tolerance but also affects the starting angle of the camshaft oil supply.

(6) The plunger groove should be aligned with the return hole of the plunger sleeve. When the plunger sleeve has two oil holes and is at the same height, although the amount of oil in the oil hole can be adjusted for the plunger groove, but because the air return hole often discharges air bubbles, the air is often discharged. When the oil is fed into the plug sleeve, the plunger groove should face the side of the fuel injection pump return passage (with the return valve assembly). Otherwise, it will affect the calculation accuracy of the fuel injection pump.

(7) Pay attention to the preload when installing the oil valve spring. Do not install without volume reduction, and do not add without volume reduction. When the oil valve sealing gasket is replaced or replaced, the size and material should be carefully selected. If necessary, match the trial installation and check the preload.

(8) Outlet valve sealing gasket that has a sealing effect on the low-pressure oil in the oil channel of the fuel injection pump,  such as 4125A diesel engine A4CB-8. × 10-75 fuel injection pump, 195 diesel engine A pump or No. 1 pump, do not be difficult because of disassembly Grind it cylindrically. Otherwise, it is easy to break the seals of the high-pressure oil circuit and the low-pressure oil circuit, so that the fuel injection pump cannot work normally. In order to ensure that the plunger does not block in the plunger sleeve, the tight seat of the oil outlet valve should be tightened according to the specified torque. The amount of torque generally varies with the injection pump model, and the same model often varies. Mainly related to the contact area of ​​the parts, the material of the oil valve sealing gasket, the processing accuracy, and the peak pressure of the pump end. If the contact area is small, the processing accuracy is high, and the peak pressure is low, the torque is small, and vice versa. After the tight seat of the oil outlet valve is tightened, it must be clamped with the eldest son to prevent loosening.

(9) After the tight seat of the oil outlet valve is tightened, the plunger that originally moved and rotated flexibly may be blocked or stuck, indicating that the plunger sleeve is under stress and deformation, and it should be reassembled or replaced in pairs; When it is eliminated, the tight seat of the oil valve can be twisted while tapping the plunger sleeve with a small hammer; do not use abrasives to grind the plunger and plunger sleeve, which will shorten the service life of the plunger couple. The top of the plunger is pressed against the oil outlet valve seat, and the burr caused by the deformation of the top will also cause the plunger to block or jam. So it must be noted that there is plunger clearance, generally should be greater than 0.3 mm.

(10) Before assembling the plunger, check the fit clearance of the plunger adjustment arm in the lever adjustment fork. If it is too large or stuck, repair the adjusting arm, adjusting fork, or replace the adjusting fork. For Type A split pumps, check the adjustment gear bar and its guide holes for burrs and deformations before assembling the adjustment gear bar. If any, remove it first and pay attention to the assembly marks.


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