Recently, brother Jun, a senior maintenance technician, met such a card friend. He was proud of driving a Guosan Iveco. During the driving process, he suddenly felt that the engine was running heavy. Finally, the machine stalled for no reason. When it was started again, he obviously felt that the machine had great resistance and couldn’t hit the motor car at all, so he broke down on the road.
It is a big fault to break down on the way.After receiving a call from the customer, Junge learned that the vehicle was not driven by the owner, and the vehicle had been parked for some time before it broke down. The owner suspected that the engine cylinder was pulled.
The vehicle was towed to Junge’s maintenance station. Junge removed the front wall cover of the vehicle and turned to judge the fault. During turning, it was found that the engine was difficult to rotate, and even the resistance of piston compression could not be felt. Therefore, it is judged that the fault of the engine occurs internally, which is very likely to be the mechanical fault of the crank connecting rod mechanism in the lower part of the middle cylinder.
Disassemble the engine and check the fault points one by one.Disassemble the engine on the ground, remove the timing belt, rotate the accessory box and drive wheel by hand, and find that the whole accessory box is also difficult to rotate.
Since the oil pump of SOFIM engine is integrated in the accessory box, if the accessory box cannot rotate, the operation of the oil pump will also be abnormal, and the poor lubrication of the whole accessory box will eventually lead to jamming.
Continue to disassemble the engine. After lifting off the cylinder head, it was found that there was no strain on the cylinder wall of the four cylinders, and the collision trace with the valve was found on the top of the piston of the four cylinders. Therefore, it was concluded that the fault point was mainly in the fourth cylinder.
There may be a problem with the connecting rod bush or the copper sleeve at the small end of the connecting rod. Due to the loose hinge point, the piston moved beyond the top dead center and collided with the valve.
Turn the engine over and remove the oil pan. A large amount of metal powder is found in the oil pan. The big end of the four cylinder connecting rod has changed color caused by high temperature.
When the big end of the connecting rod is removed, it is found that the upper and lower connecting rod pads have been engaged together and tightly held on the crankshaft. The crankshaft journal is seriously worn and the crankshaft is scrapped.
The engine was completely disassembled and inspected, and the main bearing bush was seriously strained. The bearing bush rotates in the shaft seat together with the crankshaft, commonly known as walking the outer circle.
Fault cause analysis.On the surface, the fault phenomenon: the driving gear of the accessory box is stuck, the bearing bush is seriously worn, and the bearing hole of the cylinder block is deformed. The reason is that because the oil pressure is too low, each friction pair can not get good lubrication, resulting in dry friction.
The low oil pressure may be caused by the oil itself, the pressure relief of the oil passage, or the abnormal operation of the oil pump caused by the failure of the drive gear of the accessory box. After careful observation, it is found that the engine is not caused by the three reasons mentioned just now. The oil pressure is too low.
Finally, the inspection found that the oil pan that did not attract people’s attention was deformed. It was supposed to be flat, and the bottom was connected with an inward big pit by an unknown object!
In order to determine the relationship between the deformation of the oil pan and the low oil pressure, try to install the filter collector and the oil pan. It is found that the oil inlet of the filter collector is almost blocked by the deformed oil pan, and a bright annular trace has appeared at the contact between the oil pan and the oil inlet of the filter collector.
So far, we have restored the whole process of scrapping the engine: deformation of the oil pan → blocking the oil inlet of the filter collector → insufficient oil absorption of the oil pump → low oil pressure → locking of the connecting rod bush + rolling bush of the main bearing bush + gear jamming of the accessory box → anchoring.
This kind of fault does not happen suddenly. If the driver pays attention to the instrument during driving and stops immediately when he finds that the oil pressure is insufficient, the whole engine will not be scrapped. Here, the truck house and Junge remind card friends that they must timely observe the changes of instruments and indicators during driving, and check them in time in case of abnormalities. Temporary negligence may cause heavy losses.
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