Hexagonal bolts refer to fasteners composed of heads and screws. Bolts are divided into iron bolts and stainless steel bolts according to their materials, namely, hexagonal head bolts (partially threaded)-Class C and hexagonal head bolts (full threaded)-Class C, also known as Hexagon head bolts (coarse) wool hexagon head bolts, black iron screws.
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 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 increases. Large, 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, which is 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 had replaced the connecting rod bolts, there were also fracture failures. Some engines suddenly broke the connecting rod bolts during operation.

The cause of the failure:
① The tightening torque is too large and the force is uneven during assembly.Since there is no strict 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 bolts to yield deformation, causing them 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 not carefully 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. 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 lead to poor positioning of the serrations of the joint surface, which may easily cause the connecting rod cover to loosen during engine operation, which may result in the breakage of the connecting rod bolts.
③If 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 checked once and the connecting rod bolts should be replaced; if a certain cylinder has been severely pulled during operation, the connecting rod bolts should also be replaced when replacing the cylinder-piston assembly.
④Material problems, processing defects and heat treatment process problems can also cause connecting rod bolts to break during engine operation.