The causes of the camshaft fracture of Type B fuel injection pump, repair methods and preventive measures

At present, the main engineering equipment of the Engineering Corps (Division) of our army, such as the TY120 bulldozer, ZL series loader, PY160 road leveler and 75KW mobile power station, are mostly powered by the 6135 diesel engine as the mechanical power source. As the "heart" of the 6135 diesel engine, the B-type fuel injection pump often breaks its camshaft during equipment training, field pulling and other processes, seriously affecting the smooth completion of military training and exercise tasks. Based on equipment teaching and repair practice, this paper introduces the fault causes, repair methods and preventive measures of the CAM shaft fracture of the B-type fuel injection pump of the 6135 diesel engine.

1. Cause of Malfunction

The B-type pump adopted by the 6135 diesel engine is an integral plunger fuel injection pump. It is fixed on the bracket on one side of the diesel engine block through four bolts and is driven by the diesel engine crankshaft through timing gears. The camshaft of the fuel injection pump and the drive shaft of the fuel pump are connected by a coupling. The lift of the fuel injection pump CAM is 10mm, the center distance between the pumps is 40mm, and the maximum rotational speed of the fuel pump reaches 1000 revolutions per minute. Due to the high-speed operation of the fuel injection pump, the installation form of "four-point support", and improper use and maintenance, the arc surface of the pump body at the junction of the fuel injection pump and the bracket is worn (the arc surface inside the bracket is relatively less worn), and the pump body moves downward, causing the camshaft and the fuel pump drive shaft axis to shift. The camshaft of the fuel injection pump is subjected to forces such as twisting, bending and swinging, generating additional alternating stress, which eventually leads to fatigue fracture of the camshaft.

2 Repair Methods

The surface finish of the camshaft journal of the B-type fuel injection pump for the 6135 diesel engine is no less than 8, the hardness is no less than HRC45, the cylindricity tolerance is 0.10mm, and the full-length straightness tolerance is 0.05mm. It is a precision part. For the repair of a broken camshaft, the "replacement repair method" is generally adopted, that is, the camshaft is replaced. However, if the root cause of the camshaft fracture is not eliminated after the replacement and repair, it will inevitably lead to the camshaft breaking again. To prevent the camshaft from breaking repeatedly, it is usually necessary to replace the B-type fuel injection pump body or the B-type fuel injection pump assembly. This approach is neither economical nor easy to guarantee (the method of replacing the B-type fuel injection pump body requires a fuel injection pump test bench for pump calibration), especially under field conditions where the guarantee is even more difficult. After years of practice, the following three emergency methods are quite suitable for the repair of the camshaft fracture of the B-type fuel injection pump of the 6135 diesel engine under field conditions.

2.1 Original Restoration Method

The fundamental cause of camshaft fracture is the wear of the fuel injection pump body. Based on this, we can adopt the "patching" method for welding the pump body by electric welding or copper welding. The thickness and area of the patching are slightly larger than the amount of wear. After welding, the welding area is polished and leveled by filing and grinding to restore the original geometric shape of the pump body. All parts are cleaned. After installation and commissioning, it can be used. The original repair method can also be used to repair the fuel injection pump body with metal glue. That is, apply the prepared metal adhesive to the worn area. The thickness and area of the metal adhesive coating should be slightly greater than the wear amount. After the metal adhesive has solidified for 20 to 30 minutes, grind and polish the area coated with the metal adhesive, clean all parts, and it can be used after installation and debugging.

2.2 Disassembly and assembly method of parts

The material of the pump body of the B-type fuel injection pump for the 6135 diesel engine is generally cast iron or aluminum alloy. Despite the different materials, its installation dimensions and internal structure are exactly the same. Therefore, in the scrapped B-type fuel injection pump of the 6135 diesel engine, the usable pump body, camshaft and other parts can be disassembled as needed and reassembled into a complete B-type fuel injection pump. After passing the debugging test, it can be installed and used.

2.3 Additional Parts Method

Under field conditions, when the "original component repair method" and the "parts disassembly and assembly method" cannot be utilized, the "additional parts method" can be adopted. The specific method is as follows: ① Use a file and abrasive sandpaper to polish and smooth the worn parts of the pump body (the worn parts are the mating surface with the support, and the end near the oil pump drive shaft is more severely worn). ② Use a depth caliper to measure the depth of the worn parts of the pump body after grinding. The wear depth is generally between 0.5 and 1mm. ③ Gaskets made of copper or iron sheets to form additional parts. The thickness of the additional parts is determined based on the depth of the wear area measured. The width of the additional parts is approximately equal to the thickness of the support, and the length of the additional parts is approximately equal to the arc length of the wear area of the pump body. ④ Attach the fabricated gasket between the worn parts of the bracket and the pump body. The number of additional gaskets is determined based on the depth of the wear area measured, and generally should not exceed three. After installation and adjustment, start the test run and put it into use.

3 Preventive Measures

The wear of the B-type fuel injection pump body of the 6135 diesel engine is mainly caused by the relative loosening between the pump body and the bracket. Therefore, prevention can be carried out from the following three aspects.

3.1 Installation must be correct

The B-type fuel injection pump of the 6135 diesel engine is often disassembled as a whole for repair and reinstallation after pump calibration due to reasons such as uneven fuel supply to each cylinder and inaccurate fuel supply interval angles. When installing, please pay attention to the following points: ① The fixing bolts should be tightened diagonally. If the two bolts on the outer side or the side close to the engine block are tightened first, on the one hand, it may cause the adjusted fuel supply advance Angle to be damaged. First, tighten the two fixing bolts on the side close to the machine body and advance the fuel supply advance Angle. First, tighten the two fixing bolts on the outside. The fuel supply should be postponed in advance. On the other hand, it may cause the camshaft axis of the fuel injection pump to be offset from the drive shaft axis of the fuel injection pump during installation. After the engine starts, the camshaft is directly subjected to additional alternating stress and fatigue fractures. The fixing bolts should be tightened in 2 to 3 steps. ③ The tightening torque of the fixing bolts should be between 1.5 and 2.5 kilograms of force (the fixing bolts have fine threads of M8×1 or M10×1. Excessive tightening torque is prone to damage the thread). All the fixing bolts should be tightened in place. In practice, it often occurs that the two fixing bolts on the side close to the machine body are not tightened properly due to the limitation of the installation position, while the two fixing bolts on the outside are tightened excessively instead.

3.2 Maintenance should be appropriate

The B-type fuel injection pump of the 6135 diesel engine is an important component of the fuel supply system of the diesel engine. During the usage and maintenance process, the following three points should be noted: ① The quantity and quality of the engine oil in the oil pump must meet the requirements. If the lubrication is poor, it may cause premature wear of the transmission components inside the pump at the least, and at the worst, it may lead to the bearing getting stuck and the camshaft being twisted off. ② The axial clearance of the camshaft should be appropriate. The axial clearance of the camshaft is generally around 0.03 to 0.15mm. If the clearance is too large, the camshaft will wear out faster, the engine will run unsmoothly, and it will cause early wear of the pump body. ③ The oil supply advance Angle of the oil pump and the oil supply interval angles of each cylinder should meet the requirements. If the fuel supply advance Angle and the fuel supply interval Angle of each cylinder do not meet the requirements, it will not only make the engine's power performance and economy deteriorate, but also cause difficulty in starting the engine, unstable operation, and accelerate the wear of the pump body.

3.3 Inspections should be timely

The loosening condition of the pump body and bracket of the B-type fuel injection pump of the 6135 diesel engine is generally inspected during weekly maintenance. If any abnormal condition of the engine or loosening of the pump body is found, it should be checked and tightened in time. The method for checking the tightness shall be carried out in accordance with the aforementioned installation requirements.

The above is an introduction to the causes, repair methods and preventive measures of the camshaft fracture of the B-type fuel injection pump in the 6135 diesel engine. Practice has proved that the above-mentioned emergency methods and preventive measures are scientific, reasonable, feasible and practical, and have high military and economic benefits. For colleagues' reference.