Repair and Scraping of Crankshaft Bearings for Diesel Engines Part 1

The basic process of repairing the main bearing (crankshaft bearing) of a diesel engine, the requirements for the contact area of the journal, and the handling of the relationship between the tightness and contact area are basically the same as those of the connecting rod bearing (connecting rod bearing). But the connecting rod bearing is a single fitting, while the crankshaft bearing is supported by several crankshaft bearings, which requires that the center lines of each repaired crankshaft bearing must be consistent. Therefore, the horizontal line should be corrected first, and then the bearings should be combined.

1. Before repairing and scraping the horizontal line, first check whether each bearing is on the same horizontal line when the diesel engine bearing is installed into the seat hole. Inspection method: Apply a layer of red lead oil on the crankshaft journal and place the crankshaft on the cylinder block with bearing shells. Install the bearing shell cover and tighten the bolts appropriately (using a lever about 60cm long to pry the crankshaft with arm force is recommended). Pry the crankshaft several times, then remove the bearing shell cover, lift the crankshaft, and check the contact between each bearing shell.

If the contact area between each bearing shell is significantly different or some bearings do not make contact at all, additional bearings should generally be selected. If the bearing shells are not consistent but similar, the heavy contact area of the lower bearing shell can be scraped off until it reaches 75% or more of the contact area. At this point, the horizontal line of the lower bearing shell is calibrated (there are three common structural forms of the crankcase: base type, tunnel type, and suspension type. When calibrating the horizontal line, the first two are calibrated for the lower bearing shell, and the latter is calibrated for the upper bearing shell). In the process of correcting the horizontal line, as the horizontal lines of each bearing are very different and they affect each other, it is necessary to regularly and accurately observe and analyze the changes and reasons of each bearing, and pay attention to the following two points.

It is best not to scrape the upper tile before the horizontal line is calibrated, otherwise it may cause adverse phenomena such as poor contact and excessive looseness of the upper tile even when the torque has reached the specified value before the horizontal line is calibrated.

After the horizontal line is calibrated, it is best not to use the method of scraping the lower tile to achieve appropriate tightness, except for a few heavier parts of the lower tile that need to be scraped off appropriately. Otherwise, the calibrated horizontal line may be damaged again.

2. After aligning the horizontal lines of each bearing bush, pick up the crankshaft and install the main bearing bush cover according to the markings. Tighten the bolts in a certain order one by one, rotate the crankshaft several times for each tightening, loosen the bolt of that one, and then tighten the other. After all of this is done, remove the main bearing bush cover and repair the bearing bush alloy according to the contact surface condition.

The scraping method is the same as that of the connecting rod bearing. The sequence of tightening tile covers:

Three bearing shells: 2, 1, 3.

4 bearing shells: 2, 3, 1, 4.

5 bearing shells: 3, 2, 4, 1, 5.

7 bearing shells: 4, 2, 6, 3, 7, 1, 5.

Dingbo Power was founded in 1974 and is one of the earliest manufacturers of generators and diesel generator sets in China. If you want get more information, please feel free to send email to sales@dieselgeneratortech.com we will pay highly attention on your question.