**Analysis and Treatment of the Origin of Crankshaft Cracking** Home > Bearing Knowledge > Discussion and Disposal of Crankshaft Cracking in the Initiator *Created on 2018/5/16* var cpro_id = "u3440131";

Analysis and Treatment of the Origin of Crankshaft Cracking

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/*250*250 was created on 2017/12/25*/ var cpro_id = 'u3171089';

A CPB14RHH Japanese heavy-duty truck, with a launcher model from Japan Nissan NE6, experienced ablation of the third cylinder connecting rod due to oil edge issues after traveling 300,000 km. The crankshaft showed no damage during flaw detection. However, after approximately 20,000 km, the crankshaft cracked at the junction between the third cylinder connecting rod journal and the fourth main journal. We initially suspected poor driving conditions, but the crankshaft could not withstand additional load after being enlarged. This often occurred due to overloading or improper cargo handling. A new crankshaft was replaced. However, after more than 20,000 km, the second cylinder connecting rod journal and the third main journal joint also cracked. This incident prompted us to pay close attention to the issue. ### 1. Summary of the Origin of Crankshaft Cracking Common causes of crankshaft cracking include: - Overloading - High-speed or overspeed operation - Frequent sudden braking - Poor road conditions - Improper driver behavior - Uneven crankshaft material - Poor fatigue resistance - Loose main bearings - Deformation of the main bearing housing ### 2. Analysis and Detection Based on the above reasons for crankshaft cracking, we interviewed the driver and his assistant. They provided detailed information about the vehicle's usage. According to the driver, the car had been modified to have a more powerful engine, which gave an illusion of improved performance. Recently, it had been driven mostly on city roads, with moderate speed and no frequent braking. The driver had been working for our company for 20 years, with extensive driving experience. Based on the recent operational conditions, it is clear that factors such as overloading, sudden braking, and poor road conditions can be ruled out. ### 2.2 Detection In addition to the "uneven crankshaft material and poor fatigue strength," which are difficult to detect, we conducted a thorough inspection of the crankshaft after disassembling the engine. No old cracks were found, and the wear on the connecting rod bearing and the contact surface of the connecting rod tile appeared normal. When checking the main bearing tiles, we removed the cover, tightened the bolts according to specifications, and measured the bore using a dial gauge. The error was less than 0.01 mm. However, there were slight scratch marks on the third and fourth seat holes. Using the oil passage hole as a reference, we measured the seven-hole error with a steel ruler and found that the third and fourth holes differed by 0.5 mm from the others. This indicated that the crankshaft had been damaged due to scratches and deformation in the hole seats. ### 3. Correction and Disposal The vehicle had traveled nearly 400,000 km, indicating it was nearing the end of its service life. Replacing the entire cylinder would not be economically viable. However, considering the overall functionality of the vehicle, it still held value. Therefore, we opted for a machining solution: we purchased a new crankshaft, increased the main bearing housing bore by 2 mm, and manufactured thickened 2 mm spindle bushes from the head. After processing, the crankshaft was installed and has now run for over 40,000 km. From the sound, smoke color, power, and fuel consumption, the vehicle is functioning normally.

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