Reasons for Diesel Engine Connecting Rod Bolt Breakage

Normally, the connecting rod bolts of a diesel engine are for single use and should not be reused. If the connecting rod bolts are reused, due to the increased stress, the bolts will stretch. This can easily cause the bearing shells to spin or burn out because the tightening force of the bolts is insufficient.

Meanwhile, due to the insufficient tightening force, the clearance between the bearing shell and the crankshaft journal increases, resulting in low oil pressure. This causes excessive wear of the bearing shells and leads to a bearing burnout accident. So, what are the reasons for the failure of diesel engine connecting rod bolt breakage? Below, the editor of Dingbo Power will introduce them to you in detail:

1.When the diesel engine experiences a runaway fault or the piston seizes in the cylinder during operation, the connecting rod bolts will be pulled off. If the engine has experienced a runaway fault during use, a comprehensive inspection of the engine should be carried out, and the connecting rod bolts should be replaced. If severe cylinder scoring occurs in individual cylinders during operation, the connecting rod bolts should also be replaced when replacing the cylinder piston components.

2.Excessive tightening torque and uneven force during assembly. Since no torque wrench is strictly used during assembly and the specific tightening torque is not well - understood, it is wrongly thought that the tighter, the better. A long extension rod is used to tighten the connecting rod bolts, resulting in excessive tightening torque that exceeds the yield limit of the bolt material. This causes the connecting rod bolts to yield and deform, and they break due to excessive elongation under impact loads. It should be emphasized that the connecting rod bolts must be tightened to the standard torque. Never think that the tighter and the greater the force, the better.

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

4.Diesel engine connecting rods come in various grades, and care should be taken not to interchange connecting rods of different grades during maintenance. If the connecting rod caps are mixed up and incorrectly installed during maintenance due to carelessness, the mating surfaces of the big ends of the connecting rods will not fit tightly. This will cause the connecting rod caps to loosen during engine operation and lead to the breakage of the connecting rod bolts.

For example, the big end of the connecting rod of the WD615 series diesel engine is of the oblique - cut type, with an oblique cut angle of 45°. The mating surface between the connecting rod cap and the big end of the connecting rod uses a 60° serrated positioning structure. This structure has the characteristics of tight fit, accurate and reliable positioning, and compact structure. If the connecting rod caps are mixed up and incorrectly installed during maintenance, it will inevitably result in poor serrated positioning of the mating surfaces, which can easily cause the connecting rod caps to loosen during engine operation and lead to the breakage of the connecting rod bolts.

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