Causes Of Hexagonal Bolt Failure

① The tightening torque is too large during assembly, and the force is uneven. Since there is no strict torque wrench in the assembly, the specific tightening torque is not well understood, and it is believed that the tighter the better; a longer force rod is used to tighten the connecting rod bolt, and the tightening torque is too large, which exceeds the yield limit of the bolt material, causing the connecting rod bolt to yield and deform, and causing it to break due to excessive elongation under the impact load. It should be emphasized that the connecting rod bolts must be tightened according to the standard, and it must not be considered that the tighter and the greater the force, the better.
② The connecting rods of diesel engines are divided into multiple levels. During maintenance, care should be taken not to replace connecting rods of different levels. If the connecting rod cover is messed up or installed incorrectly due to carelessness during maintenance, the matching of the connecting rod big end joint surface will not be tight, and the connecting rod cover will loosen during engine operation, resulting in the breaking of the connecting rod bolt. The connecting rod big end of the WD615 series diesel engine is bevel cut, with a bevel angle of 45°. The connecting rod cover and the connecting rod big end adopt a 60° sawtooth positioning structure. This structure has the characteristics of close fitting, accurate positioning, reliability and compact structure. If the connecting rod cover is messed up or installed incorrectly during maintenance, it will inevitably cause the sawtooth positioning of the joint surface to be poor, which will easily cause the connecting rod cover to loosen during operation, resulting in the breakage of the connecting rod bolt.
③ The diesel engine has a runaway fault or a piston burnt in the cylinder during operation, which will break the connecting rod bolt. If the engine has a runaway fault during use, a comprehensive inspection of the engine should be carried out, and it is best to replace the connecting rod bolt; if a serious cylinder pull has occurred in individual cylinders during operation, the connecting rod bolt should also be replaced when the cylinder piston assembly is replaced.
④ Material problems, processing defects and heat treatment process problems can also cause the connecting rod bolt to break during engine operation.