On June 28, 2010, Jinan Jimin industry and Trade Co., Ltd. accepted a case that WD615 Series engine replaced its cylinder block in Shanghai in October 2009 The crankshaft (overhauled) has been running for more than 40 days, resulting in the bearing bush accident of the engine crankshaft connecting rod journal. We organize relevant technicians to analyze the cause of the accident according to the actual damage fed back by the customer and the photos of the accident phenomenon on site, combined with the damaged cylinder block and crankshaft:
Because the damage of engine parts has different causes and manifestations, for the same damage, one or more causes may occur alone or at the same time. We must analyze the essential cause of the fault through the surface phenomenon of part damage. However, in many cases, the essential cause can not be accurately judged only from the surface damage trace of a certain part. It is also necessary to understand the working time, working conditions, service conditions, maintenance status, quality of replaced parts, quality of oil and damage of relevant parts for comprehensive analysis, To find out the real cause of the fault.
Due to the non local maintenance of the engine, the crankshaft of the engine is purchased by the owner, and the replaced cylinder block is a supporting product of the main engine factory. After the shoe holding accident, some high temperature signs appeared on the upper bearing surface of the main bearing of the upper cylinder block, while some incomprehensible signs appeared on the lower bearing surface of the main bearing of the lower cylinder block.
The specific position of the crankshaft bearing bush with bearing bush is on the connecting rod journal of the third cylinder of the engine, and the crankshaft connecting rod journal has seriously adhered to the bearing bush; In accident phenomenon 1, the second main shaft diameter surface showed many strain marks, but there was no same bearing pad (red arrow area). When observing the crankshaft journal surface, it was found that there were many light refraction phenomena caused by roundness problems (shown by green arrow).
1.The engine lubrication system of WD615 (from the oil passage) is the main shaft diameter of the upper cylinder block, and the upper bearing surface is the oil inlet direction (connected with the main oil passage of the engine). If the bearing bush is installed reversely, the second main shaft diameter and the first connecting rod journal of the engine will burn out in a very short time due to insufficient lubrication, but the second main shaft diameter and the first connecting rod journal of the engine will not burn out in a short time (it has been running for more than 2 months); we preliminarily judged that the extreme situation of the deviation in the number of upper and lower bearing shells is likely to occur during the assembly of main bearing shells; similar to the normal WD615 engine, a total of 14 main bearing shells are used (of which the upper 7 are with oil inlet holes and the lower 7 are without oil grooves), this engine may have 8 upper and 6 lower bearing shells during the assembly process.
Moreover, according to the distribution of the engine’s lubrication system, the oil supply of the third cylinder connecting rod journal with bearing is from the oil of the fourth main shaft diameter to the third cylinder connecting rod journal through the inclined oil hole of the crank arm. Therefore, the normal condition of this bearing bush is not directly related to whether the bearing bush of the second main shaft diameter is installed reversely or wrongly!
2. Through macroscopic observation on the surface gloss of engine crankshaft, it is found that there are many light refraction conditions caused by roundness problems. Let’s compare them with real pictures first:
They are all WD615 crankshafts, but it is obvious that the two crankshafts have different light refraction on the journal surface due to roundness problems under light irradiation.
Next, let’s look at the problem of light refraction affected by different roundness by establishing digital simulation. SolidWorks is used to establish the mathematical model of journal surface. As a comparison, one uses a circle with a radius of 50mm and the other uses a polygon with an included angle of 6 degrees of equal outer diameter to simulate:
After rendering, it can be seen that the scattering state of light can be caused only when the roundness is unqualified (polygon occurs)!
Therefore, it can be preliminarily inferred that the crankshaft with bearing pad is likely due to the out of roundness of the crankshaft, resulting in intermittent connection of the oil film of the engine lubrication system; After running for a period of time, under the condition of heavy load operation of the engine, when the impurities in the engine oil are doped on the surface of the connecting rod journal and destroy the lubricating oil film at the same time, the high temperature caused by too small local clearance will soon form the phenomenon of bearing shoe once local bonding is formed.
1. It is possible that the Bush holding phenomenon of this engine is due to the out of roundness caused by problems on the crankshaft surface during machining.
2. During the maintenance of the engine, the maintenance personnel may not have made detailed measurement and macro observation of the crankshaft.
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