2. Damage to the bearings may be caused by insufficient lubrication, foreign particles getting on them, engine overload or corrosion (see illustration). Regardless of the cause, it must be eliminated before reassembling the engine.
14.2 Typical damage to bearings
A Scratched by foreign particles - grains are visible, immersed in the working layer of the liner
B Lack of oil - the top layer is worn off
C The inserts are incorrectly positioned during installation - there are shiny spots (polished) areas
D The neck is tapered - the top layer is removed from the entire surface
E Wear of the liner edge
F Fatigue fault - craters or pockets formed
3. To inspect the bearing shells, remove them from the cylinder block/caps/connecting rods. Lay them out on a clean work surface in the same order as they are in the engine. This will help you determine which bearing is causing the problem.
4. Dirt and foreign particles enter the engine in various ways. They can be left in the engine after overhaul or pass through filters or the crankcase ventilation system. Often there are metal grains left after regrinding or formed during normal engine wear. Foreign particles that get into the bearings are embedded in the soft working layer of the liners, where they are easy to detect. Large particles do not sink into the material of the liners, but scratch the liners and journals. The best way to prevent bearing failure for this reason 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. These may include: overheating (makes the oil less viscous, which causes its layer on the bearings to become thinner), overload (squeezes oil from the bearing surface) or leaks (bearing clearances are excessive, oil pump is worn out or engine speed is high). Blockage of the lubrication passages, which is usually the result of misalignment of the bearing lubrication holes, also leads to a lack of lubrication and causes bearing failure. When a bearing fails due to lack of lubrication, the bearing layer is worn or peeled off from its steel base. The temperature can rise to such a level that the steel base turns blue from overheating.
6. Driving style also affects bearing life. Full throttle and long hours at low revs (engine overload) put a very high load on the bearings, which causes the oil film to be pushed away from the liners. As a result, the liners bend and a network of small cracks forms on them (a "fatigue" failure). Ultimately, the working layer of the bearing liner will disintegrate into pieces and break away from the steel base.
7. Short trips cause corrosion of the bearings because the engine does not heat up enough to repel compressed water vapor and corrosive gases. The vapors are adsorbed by the engine oil, forming acid and sludge. When this oil gets into the engine bearings, the working layer of the bearing shells oxidizes.
8. Incorrect selection of the bearing shell will also cause bearing failure. Shells that are too large and fit tightly into the bearing will leave insufficient operating clearance, which will result in insufficient lubrication.
9. As mentioned at the beginning of this Chapter, the bearings should be replaced after each removal during an engine overhaul.
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