On June 3, 2011, a relatively serious cylinder tamping accident occurred not long after a customer in Jinan sold four supporting in bulk. Since the customer did not provide all the pictures of damaged parts, we can only organize relevant technicians to analyze the cause of the accident according to the pictures of piston, cylinder block, camshaft and crankshaft provided by the customer:
1. The piston has an overall fracture between the piston head and skirt from the pin seat hole;
2. The engine cylinder liner is cracked near the lower part of the piston stroke BDC;
3. At least one perforation caused by instantaneous impact occurs in the cylinder block (two side perforation occurred in this accident);
4. There are obvious collision marks between the connecting rod bearing cap corresponding to the tamping cylinder and the outside of the connecting rod body;
5. The camshaft is broken;
6. Crankshaft flywheel bolt is cut off;
In this accident, the piston fracture seemed to be the focus of the user’s query, but it could not withstand the detailed scrutiny of the damage of parts and components;
Combined with the partial drawings of the piston connecting rod group in the longitudinal sectional view of the engine, we can see that assuming that this type of fracture occurs when the piston moves to the bottom dead center, it is unlikely that the small end of the connecting rod with the piston pin will leave the cylinder liner bearing hole under any state. If the piston breaks, When the engine is still working, the piston fracture residual head in the figure above will certainly be collided by the small end of the connecting rod or the piston pin due to upward loss of positioning, but there is no impact trace in the figure above.
The piston is called the heart of the engine. It is one of the most important parts in the engine. Because the piston is constantly doing high-speed reciprocating motion under the action of high-temperature and high-pressure gas, it bears the thermal load and mechanical load of high-temperature and high-pressure, and its working conditions are very bad. The piston is the only aluminum part in the main moving parts of Steyr engine. The failure of any related part in the engine or the working state of the engine is likely to cause the piston to be damaged or broken. Therefore, the engine failure is often exposed to the piston, but the part that really causes the engine failure is not necessarily the piston, Specific analysis needs to be carried out according to specific conditions. Many friends don’t know how to analyze a pile of damaged parts. In fact, they can see the essence through the phenomenon. After mastering enough basic knowledge, they can still analyze it as long as they deliberate carefully!
The yellow arrows in the figure above are the damaged parts in this accident, and the blue arrows are the damaged parts in similar accidents. The fault performance characteristics are of the same type. In the figure above, it can be seen that there are serious impact traces in the middle of the damaged connecting rod body, and there are traces formed by impact and extrusion due to the bearing cap and camshaft;
Judging from the marks and size of the cylinder block, the picture on the left is not large in volume, which is inconsistent with the marks formed by abnormal tamping of the piston pin and connecting rod. The picture on the right is the marks formed by extrusion after the camshaft is broken. Combined with the instantaneous cutting of the flywheel bolt of the engine crankshaft, after the crankshaft locating pin is broken, assuming that the engine is suddenly blocked and stopped, if the whole vehicle is instantaneously subjected to a driving inertia converted to a huge torque shear force formed by the clutch part under heavy load, if the fatigue strength of the flywheel bolt exceeds, the fracture is very normal.
Many phenomena reflected in this accident are mainly caused by overload of connecting rod or overload of connecting rod bolt. Because there is no description of maintenance parameters and relevant maintenance processes, including the operation methods before conditions occur during vehicle operation, we can only briefly describe them.
The use and maintenance industry has now formed a habit. When something breaks down, it is the car that is bad. When the car is repaired, the repair shop says that the parts are bad. In China, it is the impetuous society that has caused too many similar sad things.
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