Analysis and treatment of the origin of crankshaft cracking

**Analysis and Treatment of Crankshaft Cracking in the Initiator** 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** Source: China Bearing Network | Time: 2013-04-23 --- A CPB14RHH Japanese heavy-duty truck, with a Nissan NE6 model launcher, experienced issues when it reached 300,000 km. The third cylinder connecting rod was ablated due to oil edge problems. However, the crankshaft was not found to have any flaws during flaw detection. After traveling about 20,000 km, the crankshaft cracked at the joint between the third cylinder connecting rod journal and the fourth main journal. We initially suspected poor driving conditions, but after the crankshaft was enlarged, it could no longer handle extra loads, often caused by overloading or improper cargo. The solution was to replace the entire crankshaft. However, after running more than 20,000 km again, the crankshaft cracked at the joint between the second cylinder connecting rod journal and the third main journal. This incident raised serious concerns and led us to conduct a thorough investigation. ### Summary of Common Causes of Crankshaft Cracking Crankshaft cracking can be attributed to several factors: - Overloading during travel - The engine frequently operating at high or overspeed - High-speed driving - Sudden braking - Poor road conditions - Improper driver operation - Uneven crankshaft material - Poor fatigue resistance - Loose main bearings - Deformation of the main bearing housing ### Analysis and Detection After considering the above causes, we interviewed the driver and co-driver to better understand the vehicle's usage. The driver reported that the machine had been modified to be more powerful, which created an illusion of improved performance. Recently, the vehicle had been running mainly on city roads, with moderate speeds and no signs of sudden braking. The driver had been with our company for 20 years and had extensive experience. Based on recent operational data, it seems that factors like overloading, sudden braking, or poor road conditions were unlikely. During the inspection, we found no old cracks or damage on the crankshaft. The connecting rod bearings and their contact surfaces showed normal wear. 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 0.01mm. However, there were slight scratch marks on the third and fourth main bearing holes. Further measurements revealed a 0.5mm discrepancy between these holes and the others. This indicated that the crack originated from the hole scratches and deformation. ### Correction and Disposal The vehicle had traveled nearly 400,000 kilometers, nearing the end of its service life. Replacing the entire engine would not be cost-effective. However, from a functional perspective, the vehicle still had value. To address the issue, we opted for a machining solution: purchasing a new crankshaft, enlarging the main bearing housing bore by 2mm, and creating thickened 2mm bushings. After processing, the engine ran smoothly for over 40,000 km. It was evaluated based on sound, smoke color, power, and fuel consumption, and the vehicle functioned normally. --- **Related Bearing Knowledge** - Classification of NSK Imported Bearings' Inner Packaging - Characteristics of Four-Point Contact Ball Bearings - How to Distinguish Whether Needle Roller Bearings Can Be Reused - Methods of Common Damage in TIMKEN Bearings --- This article is linked to http:// Please indicate the bearing network: http:// Previous: Bearings Common Sense (Part I) Next: The Use and Development of RH’s Elite Skills in Bearing Production

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