Inspection
1. Although the main and connecting rod bearing shells should be replaced during an engine overhaul, keep the old bearing shells for detailed inspection as they can provide valuable information regarding the condition of the engine (see illustration).
2. Bearing damage may be caused by lack of lubrication, foreign matter intrusion, motor overload, or corrosion. Whatever the cause, it must be corrected before the engine can be reassembled.
3. Remove all main and connecting rod bearing shells and lay them out on a clean work surface in the same order as they are installed in the engine. This will allow you to link the bearing damage to the corresponding crankshaft journal. Do not touch the inner surface of the earbuds, you may damage it.
4. Foreign particles enter the engine in various ways. They can be left in the engine during reassembly, or get through filters or the crankcase ventilation system. Often there are grains of metal left after regrinding or formed during normal engine wear. Foreign particles caught in the bearings interspersed in the soft working layer of the liners, where they are easy to detect. Large particles do not sink into the liner material, but scratch the liner and neck. The best way to prevent bearing failure from this cause is to thoroughly clean all components and maintain impeccable cleanliness during engine assembly. In addition, it is recommended to change the engine oil and filter frequently and regularly.
5. Lack of lubrication has many interrelated causes. They can be: overheating (makes the oil less viscous, which thins its layer on the liners), overload (pushes oil away from the bearing surface) or leaks (bearing clearances excessive, oil pump worn or engine speed too high). Blockage of the lubrication channels, which is usually the result of misalignment of the lubrication holes of the bushings, also leads to a lack of lubrication and damage to the bearing. When the cause of a bearing failure is a lack of lubrication, the wear layer of the bearing will wear off or peel off from its steel backing. The temperature can rise to such a point that the base steel turns blue from overheating.
6. Driving style also affects bearing life. Full throttle and extended low speed operation (engine overload) give a very high load on the bearings, which leads to the displacement of the oil film from the liners. As a result, the liners bend and a network of small cracks forms on them (malfunction «fatigue»). Eventually, the wear layer of the bearing shell will break into pieces and break away from the steel backing.
7. Short trips lead to corrosion of the liners, as the engine does not heat up enough to repel compressed water vapor and corrosive gases. Vapors are adsorbed by engine oil, forming acid and sludge. When such oil enters the engine bearings, the working layer of their liners is oxidized.
8. Incorrect bearing selection will also result in bearing failure. Bushings that are too large and fit tightly into the bearing leave insufficient running clearance, resulting in a lack of lubrication.
9. When assembling, do not touch the working surface of the earbuds with your fingers, as you may scratch it.
10. As mentioned at the beginning of this Chapter, the liners should be changed after each removal.
Selection of main and connecting rod bearings
11. On sale there are liners of main and connecting rod bearings of both nominal and repair sizes (see specs).
12. After installing new liners, check the working clearances of the crankshaft bearings (see chapter 12).
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