Examine and Repair of Crankshaft

Common damage to crankshafts are cracks, journal wear and shaft bending.

1. Inspection of crankshaft cracks

After cleaning the crankshaft, put it on the bracket, and hit each crank arm with a hammer. If it makes a crisp "clang, clang" sound, it means that there is no crack. If it makes a hoarse dull sound, it means that there is a crack. Generally, the cracks are located at the connection between the journal and the crank and around the lubricating oil eye. In order to further find out where the crack is, use a microscope to observe carefully, or soak the crankshaft in kerosene, wipe the surface of the crankshaft, and evenly apply a layer of white powder on the journal, and then tap the crank arm with a hammer. If the crankshaft has cracks, oil will seep out from the cracks and turn the white powder into yellow-brown. The length of the journal along the circumference of the oil hole does not exceed 5mm, or there are longitudinal cracks that do not extend to the arc and the oil hole. Repairs are allowed when the length does not exceed 15mm.

2. Inspection of crankshaft bending

Support both ends of the crankshaft on the "V-shaped frame on the flat plate. Use a dial indicator to measure, touch the probe of the dial indicator to the main journal in the middle of the curve, slowly rotate the crankshaft by hand, and observe the dial indicator pointer. Change, when the runout of the dial indicator (circular runout) is less than 0.15mm, it can be corrected by grinding the journal. When the curvature is greater than 0.15mm, it should be corrected. When the curvature exceeds 0.20mm, it should be scrapped. The bending of cranshaft is very important for its link with connection rod.

3. Measurement of the worn parts of the crankshaft.

The wear amount, roundness and cylindricity of the journal should be measured with an outer diameter micrometer. Two positions (I-I and I-I) should be measured along the axial direction on each journal, and a mutually perpendicular measurement should be carried out at each position. Measurements in both directions (A-A and B-B). The difference between the diameters of I and I measured in the same direction is the cylindricity; the difference between the diameters of A and B measured at the same position is the roundness; the minimum diameter measured and the standard diameter (or the last repair size ) is the wear amount of the journal. The roundness and cylindricity values ​​of journals refer to the values ​​specified in the standard. If it exceeds the specified value, the crankshaft should be polished. The crankshaft is the most important parts in engine spare parts, if there is any wearing in crankshaft, it has to be examined and relaired. 

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