Causes Of Bolt Failure

The connecting rod bolts of diesel engines are one-time use and are not allowed to be reused. If the connecting rod bolt is reused, due to the large force and the elongated bolt, it is easy to cause the bush to burn the bush due to the insufficient tightening force of the bolt; at the same time, due to the insufficient tightening force, the clearance between the bush and the crankshaft journal Increased, resulting in low oil pressure, resulting in excessive wear of the bearing bush and burnout. The diesel engine is a high-strength diesel engine, and the connecting rod is subjected to a larger impact load than the ordinary diesel engine. The repeated use of the 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 have broken failures, and some engines have suddenly broken the connecting rod bolts during operation.

Cause of failure:

① The tightening torque is too large during assembly, and the force is uneven. Because there is no strict torque wrench [1] in the assembly, the specific tightening torque is not well understood. It is believed that the tighter the better; the longer torque bar used to tighten the connecting rod bolts, the tightening torque is too large and exceeds The yield limit of the bolt material is exceeded, which causes the connecting rod bolt to yield deformation, causing it to break due to excessive elongation under the effect of impact load. It should be emphasized that the connecting rod bolts must be tightened according to the standard, and the tighter the stronger, the better.

②The connecting rods of diesel engines are divided into multiple grades. During the maintenance, it should be noted that connecting rods of different grades cannot be used. If the connecting rod cover is not carefully messed up or misinstalled during maintenance, the coupling of the large connecting surface of the connecting rod will not be tight, and the connecting rod cover will become loose during engine operation and cause the connecting rod bolt to break. The big end of the connecting rod of WD615 series diesel engine is oblique cut type, the angle of bevel is 45 °, the connecting surface of the connecting rod cover and the big end of the connecting rod adopts 60 ° zigzag positioning structure, which has close fitting, accurate positioning, reliable and compact structure specialty. If the connecting rod cover is messed up or misassembled during maintenance, it will inevitably result in poor positioning of the jagged teeth on the joint surface, which will easily cause the connecting rod cover to loosen during the operation of the engine and cause the connecting rod bolt to break.

③During the running of the diesel engine, or the piston burned in the cylinder, the connecting rod bolts were broken. If the engine has experienced a speeding failure during use, a full inspection of the engine should be performed, and it is best to replace the connecting rod bolts; if the individual cylinders have experienced serious pulling cylinders during operation, the connecting rod should also be replaced when replacing the cylinder piston assembly Bolt replacement.

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

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