Repair Of Worn Crankshaft

Generally speaking, the journal diameter is below 80mm, and the roundness and cylindricity error exceeds 0.025mm; Or a journal diameter of more than 80mm. Crankshafts with roundness and cylindricity errors exceeding 0.0400 shall not be repaired or ground according to the specified dimensions, or shall not be ground or repaired before purchasing the specified dimensions after vibration surfacing, chromium plating, or tin plating.

1. Crankshaft grinding

The grinding of the crankshaft journal is based on the correction of the crankshaft. In addition to meeting the technical requirements for the dimensional accuracy and surface roughness of the journal surface, crankshaft grinding also meets the requirements for shape tolerance. When grinding the crankshaft, ensure the coaxiality of each axis of the journal and connecting rod journal and the parallelism between the two axis lines, and limit the radial error of the crankshaft. Ensure the accuracy of the position and angle between the connecting rod journals. Grinding of the crankshaft is usually carried out using a dedicated crankshaft grinder.

2. Grinding of connecting rod journal

Due to uneven wear of the connecting rod neck, two grinding methods, eccentric grinding and concentric grinding, have emerged.

Concentric grinding means that the axis position of the connecting rod journal is kept certain after grinding, that is, the crankshaft radius and distribution angle are kept certain. When grinding the crankshaft, the concentric method is often used to keep the crankshaft radius constant and the compression ratio of the diesel engine constant, but the amount of grinding is large each time. Currently, during the use of automobiles, the number of major repairs is reduced, and the concentric method can ensure that the performance of the engine remains unchanged.

The eccentric grinding method locates grinding according to the worn surface of the connecting rod journal. At this point, the centerline position of the journal and the radius of the crankshaft change. Generally, the radius of the crankshaft after grinding is larger than the original radius of the crankshaft, increasing the compression ratio, and uneven changes in various cylinders. At the same time, the overall mass center of the crankshaft is not located on the centerline of the crankshaft neck, causing imbalance in the crankshaft, causing movement of the crankshaft. Therefore, when grinding the connecting rod journal, minimize the increase in the crank radius as much as possible, so that the coaxiality error of the centerline of the odd and even connecting rod journals is less than 0.10 mm, to ensure balance in the operation of the crank.