A truck, traveling 300 thousand kilometers, due to lubrication oil cause second cylinder connecting rod ablation, through the flaw detector to detect the crankshaft has no scar, the crankshaft increase the correction, repair the engine. Driving for about 20 thousand kilometers, the fracture in third cylinder connecting rod shaft neck and neck joint fourth main section, we think traffic is poor, can not afford to increase the rated load of crankshaft after work.

Is often rated cargo or even overloaded work caused. Therefore the replacement of a new crankshaft, crankshaft and driving second cylinder connecting rod fracture in the neck and neck joint third main section after more than 20 thousand kilometers, the accident caused our attention.

1 crankshaft fracture reason

The reasons for the crankshaft fracture of the North V3 fittings are summarized as follows:

The overload driving, often in the engine speed or overdrive; high speed travel, often brakes; poor road conditions, improper operation of the driver; the uneven material, poor anti fatigue strength of the crankshaft itself; injury; lubricating oil quality is poor, with a holding tile phenomenon; main bearing looseness; main bearing hole deformation.

2 Analysis and detection

2.1 ask

According to the reasons above beiben fracture V3 parts of the crankshaft, we talked with the driver and his deputy, carefully understand the use of the car, the driver of the car engine reflected after repair, and powerful engine sounds small, no black smoke, the normal fuel consumption. Recently all run in the city on the road, the speed is not fast, no previous brake phenomenon, the driver is driving a car for 20 years old driver, driving experience. And according to the recent operation of our company, it can be proved that the above talk is true. Therefore, we can exclude the reasons for “overloading, driving, braking, road conditions” and so on.

2.2 detection

In addition to the above-mentioned crankshaft uneven material, anti fatigue strength is poor “temporarily unable to test, the engine after dissection from ground surface observation of the fracture, no old scars; and the connecting rod connecting rod bearing tile with surface normal wear, no holding tile phenomenon; demolition of main bearing tile, installed on the main bearing bush cover, according to the provisions of the bolt force tighten the indicator measuring aperture, the deviation is less than 0. 01mm, but third, fourth seat hole is provided with a scratch mark; and then remove the main bearing cap, according to the Kong Wei oil benchmark, measuring seven hole deviation with the steel ruler, found three or four holes and other than a difference of 0.5mm. This shows that the fracture of the crankshaft is caused by the hole scraping and the hole seat deformation.

3 repair and disposal

The car has been running for nearly 400 thousand kilometers, and considering the approaching scrap period, it would be uneconomical to replace a new cylinder block from an economic perspective. But considering the overall performance of the car, the car is still valuable. So we use the machining method: buy a new crankshaft, a large cylinder boring 2mm main bearing, to increase the 2mm crankshaft main bearing hole seat, a pair of reconstituted thick 2mm, the diameter according to the standards of crankshaft machining. Engine repair has traveled more than 40 thousand kilometers from the North Benz V3 engine accessories sound, smoke, power, fuel consumption and other aspects of the evaluation, the performance of normal car.