Reasons for the failure of high-strength bolts and nuts:
① The tightening torque is too large during assembly, and the force is uneven. Since the torque wrench is not strictly used in the assembly, the specific tightening torque is not well understood, and it is believed that the tighter the better; the connecting rod bolts are tightened with a longer afterburner rod, and the tightening torque is too large, exceeding the bolt material. The yield limit causes the connecting rod bolt to yield and deform, causing it to break due to excessive elongation under the action of the impact load. It should be emphasized that the connecting rod bolts must be tightened according to the standard. Never think that the tighter and the stronger the force, the better.
②The connecting rod of the diesel engine is divided into various grades. During the maintenance, it should be noted that the connecting rod of different grades cannot be replaced. If the connecting rod cover is messed up or wrongly installed due to carelessness during the maintenance, it will cause the joint surface of the connecting rod big end to not fit tightly, and the connecting rod cover will be loosened during the engine operation, resulting in the breakage of the connecting rod bolt. The big end of the connecting rod of WD615 series diesel engine is a bevel cut type, and the bevel angle is 45°. The connecting surface of the connecting rod cover and the big end of the connecting rod adopts a 60° serrated positioning structure. This structure has the advantages of tight fit, accurate positioning, reliability and compact structure. specialty. If the connecting rod cover is messed up or installed incorrectly during maintenance, it is bound to cause poor positioning of the serrations on the joint surface, which will easily lead to the loosening of the connecting rod cover during the operation of the engine, resulting in the breakage of the connecting rod bolts.
③If the diesel engine has a speeding failure or the piston burns to death in the cylinder during operation, the connecting rod bolt is pulled off. If the engine has a speeding failure during use, a comprehensive inspection of the engine should be carried out and the connecting rod bolts should be replaced; if there is a serious cylinder pulling in individual cylinders during operation, the connecting rod bolts should also be replaced when replacing the cylinder piston assembly. .
④Material problems, machining defects and heat treatment process problems can also cause connecting rod bolts to break during engine operation.
Precaution
①Every time you run 12,000km for secondary maintenance, the engine oil pan should be removed, and the use of the engine bearing bushes should be checked with Shenyang high-strength bolts. If the clearance of individual bearing bushes is found to be too large, they should be replaced, and the connecting rod bolts should also be replaced at the same time. If it is found that the engine is not running smoothly and there is abnormal noise during normal operation, it should also be stopped in time for inspection.
②In each maintenance, the newly replaced connecting rod bolts should be inspected, and attention should be paid to whether there are cracks or dents in the head, guide part, and thread parts of the bolts, and whether the tooth shape and pitch of the threads are abnormal.
③ When assembling the connecting rod cover, use a torque wrench and tighten it according to the specified standard to prevent the torque from being too large or too small.
④ Use the connecting rod bolts produced by the supporting factory.
