Tell the story behind, analyze the reason why the connecting rod bolt is fragile

The connecting rod bolts of diesel engines are for one-time use and are not allowed to be reused. If the connecting rod bolts are repeatedly used, due to the large force and the elongated bolts, it is very easy to cause the bearing bush to roll and burn due to the insufficient bolt tightening force; at the same time, due to the insufficient tightening force, the matching clearance between the bearing bush and the crankshaft journal Increased, resulting in low oil pressure, resulting in excessive wear of bearing bushes and bush burning accidents. 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 lead to 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 cause of the failure: ①The tightening torque is too large and the force is uneven during assembly. Since there is no strict matching torque wrench in the assembly, and the specific tightening torque is not well understood, 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.

②The 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 the maintenance, the joint surface of the connecting rod big end will not fit tightly, and the connecting rod cover will loosen during engine operation and cause the connecting rod bolt to break. WD615 series diesel engine connecting rod big end is oblique cut type, the bevel angle is 45°, connecting rod cover and connecting rod big end joint surface adopts 60°sawtooth positioning structure, this structure has close fit, accurate positioning, reliable and compact structure specialty. If the connecting rod cover is messed up or installed incorrectly during maintenance, it will inevitably result in poor positioning of the serrations on 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.

③When the diesel engine has a runaway fault or the piston burns to death in the cylinder during operation, the connecting rod bolt is pulled off. If the engine has a runaway failure during use, the engine should be thoroughly inspected, and it is best to replace the connecting rod bolt; if a certain cylinder has serious cylinder pull 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.

Precautions

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, and you should also replace the connecting rod bolts at the same time. If you find that the engine is running unsteadily or abnormal noise during normal operation, you should stop it for inspection.

②In each repair, the newly replaced connecting rod bolts should be inspected, and attention should be paid to whether there are cracks or dents in the head of the bolt, the guide part, and the thread parts, and whether the tooth shape and 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 standards to prevent excessive or small torque.

④Select connecting rod bolts produced by the supporting factory.