Briefly describe the reason why the connecting rod bolt is easy to break

Diesel engines are high-strength diesel engines, and the connecting rods are subject to greater impact load, much larger than ordinary diesel engines. Repeated use of connecting rod bolts can easily cause breakage, damage the engine cylinder block, and cause the engine to be scrapped. Although some units have replaced the connecting rod bolts, they also experienced fracture failures. Some engines suddenly broke the connecting rod bolts during operation.

　　 The connecting rod bolts of the diesel engine are for one-time use and are not allowed to be reused. If the connecting rod bolts are used repeatedly, the bolts will be elongated due to the large force, which will easily cause the bushing to roll and burn due to insufficient bolt tightening force. At the same time, due to the insufficient tightening force, the matching gap between the bearing bush and the crankshaft journal is increased, resulting in low oil pressure, causing excessive wear of the bearing bush and causing a bush burning accident.

　　Precautions (Guide: Installation steps of wire thread inserts and how to use tools)

　　①Each time you run 12000km for secondary maintenance, you should disassemble the engine oil pan and check the use of the engine bearing bush. If you find that the gap between individual bearing bushes is too large, you should replace it. The replacement should also replace the connecting rod bolt. If you find that the engine is running unsteadily or abnormal noise during normal operation, you should stop and check in time.

　　② In each repair, the newly replaced connecting rod bolts should be inspected. Pay attention to whether there are cracks or dents on the head of the bolt, the guide part, and the threads. Whether the shape of the thread and the pitch of the thread are abnormal. Resolutely not use it.

　　③When assembling the connecting rod cover, use a torque wrench to tighten it according to the specified standard to prevent excessive or small torque.

　　④Select connecting rod bolts produced by the supporting factory.

Analysis of the cause of the failure:

　　① The tightening torque during assembly is too large and the force is uneven. Since there is no strict matching torque wrench in the assembly, the specific tightening torque is not well understood, and the tighter the better; the longer the afterburner is used to fasten the connecting rod bolts, the tightening torque is too large and exceeds the bolt material The yield limit causes the connecting rod bolt to yield deformation, causing it to break due to excessive elongation under the action of impact load. It should be emphasized that the connecting rod bolts must be tightened according to the standard. It must not be considered that the tighter and the greater the strength, the better.

　　② The connecting rods of diesel engines are divided into multiple levels. During maintenance, attention should be paid to not changing to connecting rods of different levels. If the connecting rod cover is carelessly messed up or installed incorrectly during maintenance, it will cause the coupling surface of the connecting rod big end to not fit tightly, and cause the connecting rod cover to loosen during engine operation and cause the connecting rod bolt to break. The big end of the connecting rod of WD615 series diesel engine is of the oblique cut type with a 45° bevel angle. The connecting surface of the connecting rod cover and the big end of the connecting rod adopts a 60° sawtooth positioning structure. This structure has a tight fit, accurate positioning, reliable and compact structure. specialty. If the connecting rod cover is messed up or installed incorrectly during maintenance, it will inevitably lead to poor positioning of the serrations of the joint surface, which will easily cause the connecting rod cover to loosen during the engine work, and cause the connecting rod bolt to break.

　　③The diesel engine has a runaway fault or the piston burns to death in the cylinder during operation, and the connecting rod bolt is pulled off. If the engine has a runaway failure during use, a comprehensive inspection of the engine should be done, and it is best to replace the connecting rod bolts; if a certain cylinder has been severely pulled during operation, the connecting rod should also be replaced when replacing the cylinder-piston assembly Bolt replacement.

　　④Material problems, processing defects and heat treatment process problems can also cause connecting rod bolts to break during engine operation.

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