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 earbuds are incorrectly positioned during installation - there are shiny (polished) plots; D - The neck is reduced to a cone - the top layer is removed from the entire surface; E - Wear of the edge of the liner; F - Fault "fatigue" - craters or pockets formed
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. The size of the earbuds is printed on the back and this information should be given to the supplier of the new earbuds.
2. Bearing damage can be caused by lack of lubrication, foreign matter, engine overload or corrosion (refer to illustration above). Regardless of the cause, before assembling the engine, it must be eliminated.
3. To inspect the bearing shells, remove them from the cylinder block/caps/rods. Lay them out on a clean work surface in the same order as they are in the engine. This will allow you to find out in which particular bearing the problem is localized.
4. Dirt and foreign particles enter the engine in various ways. They may be left in the engine after overhaul or pass through filters or the crankcase ventilation system. Often there are grains of metal left after regrinding or formed during normal engine wear. Foreign particles that have entered the bearings are actively 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 for this reason is to thoroughly clean all components and keep the engine as clean as possible. 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 are excessive, oil pump is worn or engine speed is 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 liner is worn away or peeled off from its steel base. 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 continuous slow running (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. Short trips lead to corrosion of the liners, as 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 such oil enters the engine bearings, the working layer of the bearing shells oxidizes.
7. 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.
8. If it is necessary to install new liners, before assembling the engine, it is required to measure the operating clearances to make sure that the liners are selected correctly (refer to sectionInspection of the crankshaft). If there is any doubt as to which bearings should be used, consult your Renault representative.