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Inspection And Repair Of Common Faults Of Diesel Generator Crankshaft Journal

Mar. 15, 2023

I. Inspection of roundness and cylindricity error of diesel generator journal.


For the inspection of roundness and cylindricity errors of crankshaft journal and connecting rod journal, generally use an outside micrometer to measure at multiple points on the same cross section of the journal. The difference between the maximum diameter and the minimum diameter is the roundness error. The diameter difference measured at both ends is the cylindricity error.


The roundness and cylindricity tolerance of journal is 0.025mm for those with diameter below 80mm and 0.040mm for those with diameter above 80mm. If it exceeds, it shall be polished according to the specified repair size. In addition, you can also find the abrasion, grooving, roughness, scar and ablation of the journal by looking and touching.


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II. Repair and grinding of journal wear, roundness and cylindricity out of tolerance.


1. Repair of journal wear scar.

If the roundness and cylindricity of each journal of the crankshaft do not exceed the specified limit, but there are only slight scratches, grooves, roughness, scars and ablation, etc., a long strip of fine emery cloth with the same width as the journal can be wrapped on the journal. Then use hemp rope or cloth strip to wrap two or three circles on the abrasive cloth, and pull the two ends of the rope by hand to and fro for polishing, or use special polishing fixture for polishing.

After the scar of the journal is removed, in order to reduce the surface roughness of the journal, the abrasive on the journal and grinding clamp can be cleaned, coated with a layer of lubricating oil, and then the final polishing can be carried out.


2. Repair of out-of-tolerance roundness and cylindricity of journal.

When the roundness and cylindricity of the crankshaft journal and the connecting rod journal exceed 0.025mm or 0.04mm, it is necessary to grind and repair them according to the next repair size, or carry out vibration surfacing, and then grind them to the specified size after chrome plating.


The grinding of crankshaft is generally carried out on a special crankshaft grinder or equipment modified with an ordinary lathe. In general small repair units, some use a fine file to carefully round the journal, carefully inspect it, repeat it, and then use a rope or grinding clip to polish it according to the above method. Using this method to repair requires skilled fitters to ensure certain repair quality. General repair personnel should not follow suit.


3. Turning and grinding of journal.

For the repair dimension of journal, diesel engines have 6 levels, with each reduction of 0.25mm as the first level (0.25mm, 0.50mm, 0.75mm, 1.00mm, 1.25mm, 1.50mm), and gasoline engines have 16 levels, with each reduction of 0.125mm as the first level (0.125mm, 0.250mm, 0.375mm, 0.500mm, 0.625mm, 0.750mm, 0.875mm, 1.000mm, 1.125mm, 1.250mm, 1.375mm, 1.500mm, 1.625mm, 1.750mm, 1.875mm, 2.000mm). The maximum reduction of the journal shall not exceed 2mm. If it exceeds 2mm, it shall be repaired by overlaying, chrome plating and spray plating.


(1) Determine the repair size.

The repair dimension of upper grinding is determined as follows: repair dimension of crankshaft journal=minimum diameter of the most worn journal - machining allowance x2

The machining allowance for general dimensions is 0.05mm. The value obtained is compared with the repair dimension table to see which level of repair dimension this value is close to, and then select which level of repair dimension. After the repair size is selected, grind it on the grinder.


(2) Precautions.

① When repairing, take the most worn journal as the standard, and grind each journal to the same size. Because the wear degree of main journal and connecting rod journal is different, their repair dimensions are not necessarily the same level, and the repair dimensions of each main journal or connecting rod journal should generally be the same level.

② The round root of the crankshaft should be kept intact, and the radian of the round corner should not be reduced. Generally, the radius of the round corner is 4-6 mm.


(3) Requirements after grinding.

Its out-of-roundness and taper shall be within the specified range. Generally speaking, when D<80mm, the allowable range of out-of-roundness and taper of main journal and connecting rod journal is 0.015mm and 0.02mm respectively. When D>80mm, the allowable range of out-of-roundness and taper of main journal and connecting rod journal is 0.02mm and 0.03mm respectively.


Jiangsu Starlight Electricity Equipments Co.,Ltd., as an OEM supporting manufacturer authorized by Cummins to provide Chinese diesel generator sets, has professional manufacturing technology, perfect quality management system and strong R&D technical strength. It can provide users with generator sets of various specifications from 15KW to 2500KW. It can also provide users with one-stop service of design, supply, debugging and maintenance at any time. welcome contact us by email sales@dieselgeneratortech.com.

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