Common rail injector repair- valve assemble


Common rail injector repair- valve bonnet and valve stem matched

Engine shake, black smoke and other symptoms are often encountered in the diesel vehicle repair , reasons that lead to the above problems may be numerous and diverse, of which the greatest probability of common rail injector failure. But today, I am happy to share some knowledge regarding the common rail injector repair cases,

Repair man Mr. Yang recently repaired a FAW J6 dump truck, Xichai 6DL engine, installed 0445120393 injector. Driver’s feedback is engin weakness, and sometimes not good start.


After Yang’s  detection, the total fuel return quantity of the common rail injector is too large. So remove the six fuel injector and be tested on the common rail injector test bench, found that there are two injectors are with large fuel return quantity. So Yang replaced the two fuel injector valve components, tested on the common rail tester, and find the common rail injector working well, fuel injection and return volume are all under normal range,  loaded the injector well and driver left.

But after half a day, the Driver come back with the truck, and feedback that:the truck is intermittently shivering. Yang tested and find driver did not tell lies, the car is also intermittent black smoke serious. Doubt again the njector problem.

Master Yang once again measured the total volume of fuel injector, return quantity is only one minute more than 40 ml at idling,  well below 100 ml. Yang does not know what happened, according to detection of diagnosic scanner, the computer has no fault code, the injector is also just calibrated well, should not be a problem. So Yang contacted with us and trying to find a solution.


Our technician one again think it is common rail injector problem, and has conducted in-depth communication with Mr.yang, got that,  As there is no 657 valve set in Yang’s workshop, so he demolished two original 692 valve set,  use two new Bonnet of 692, put to the valve rod of the original injector

At this point, our technician suddenly realized the problem, So advise Yang to replace the whole new original 657 valve set, re-try again

Three days later, Yang contacted with us and tell us the problem is totally solved.


Theoretical analysis of the common rail injector valve bonnet and stem working principles


So what is the theoretical basis for such a strange phenomenon?


In fact, every one of Bosch valve components are matched parts. What is the match? Simply speaking, there is a strict gap between the bonnet and the valve stem, can not be too large nor too small, in the valve assembly production process, for each set of valve components will be strictly pneumatic clearance measurement to ensure that the gap in the established The control range (only a few microns).


If the match between the bonnet and the valve stem is too large or too small, will result in varying degrees of adverse consequences:

1. if the matching gap of the valve bonnet and valve stem is too large

1) Injector oil return will exceed the standard

If the mating clearance is too large, too much high-pressure fuel will leak into the low-pressure oil gallery of the injector from the control chamber of the valve assembly through the gap between the bonnet and the stem, resulting in excessive oil return to the injector.


2) easy to partial eccentric stem guide

If the valve assembly guide gap is too large, the stem easily in the course of the work side, leading to increased wear side of the guide surface, and ultimately affect the injector life.

2. if the matching gap between valve boonet and stem is too small

During injector operation, high pressure fuel in the control chamber of the valve assembly acts around the bonnet to create an inward pressing force. If the gap is less than the amount of deformation, the bonnet will tightly hold the stem resulting in movement block or even lock, and then the injector injection disorder. As shown below:

If the gap is only small, but will not lead to locking, valve guide is also easy to wear and affect the short usage life of the injector. The higher the rail pressure, the greater the impact.


As the aftermarket injector test bench test takes the average of thousands of times the total fuel value, therefore, for the random match the valve bonnet and valve stem components, the test of the oil is difficult to detect a single injection uneven Abnormal. Only installing the fuel injector with the valve assembly on the engine may cause the engine to become weak, smoke or shake under dynamic conditions.