Repair after Crankshaft Wear

Generally speaking, the axle journal diameter is below 80mm, the crankshaft with the roundness and cylindricity error exceeds 0.025mm; or the axle journal diameter is above 80mm, the crankshaft with roundness and cylindricity error exceeds 0.0400mm, which all should be ground according to the specified size, or carry out vibration surfacing, chrome plating, iron plating and then grinding to the specified size or repair size.

1. Grinding of the crankshaft

Grinding of the crankshaft journal is based on crankshaft correction. In addition to the dimensional accuracy and surface roughness of the journal surface, the crankshaft grinding must meet the requirements of the geometrical tolerance: When grinding the crankshaft, the coaxiality of the axial line of the main journal and the connecting rod journal and the parallelism between the two axial lines must be ensured to limit the crank radius error and to ensure the accuracy of the angle between the connecting rod journal. Grinding of the crankshaft is usually carried out on a dedicated crankshaft grinder.

2. Grinding of the connecting rod journal

Due to the uneven wear of the connecting rod journal, two grinding methods are produced: eccentric grinding and concentric grinding. The concentric grinding method is to keep the axial position of the connecting rod journal after grinding, that is, the crank radius and the distribution angle are unchanged. When the crankshaft of a diesel engine is ground, the concentric method is often used to keep the crank radius constant, and keep the compression ratio of the diesel engine constant, but the amount of grinding is large each time. Currently, during the life of the car, the number of overhauls is reduced, and the concentricity method can ensure that the engine performance remains unchanged. The eccentric grinding method is to position the grinding according to the worn journal surface of the connecting rod, at this time, the center line position and the crank radius of the journal are changed.

Generally, the crank radius after grinding is larger than the original crank radius, so that the compression ratio is increased, and the cylinders are unevenly changed. At the same time, the mass center of the entire crankshaft is not on the centerline of the crankshaft main journal, causing the crankshaft to be unbalanced, resulting in additional dynamic loads during operation. Therefore, when the connecting rod journal is ground, the increase of the crank radius should be minimized to ensure that the coaxiality error of the shaft axis of the co-located connecting rod is not more than ±0.10mm, so as to ensure the balance in the crankshaft operation.