2. Bearings fail due to lack of lubrication, dirt getting on them, engine overloads and corrosion. The cause of the bearing failure must be found and corrected before the engine is assembled.
3. Lay out the old bearings on a clean work surface in the same order as they were installed on the crankshaft. This will allow you to associate the problems that have arisen with a specific crankshaft journal.
4. Dirt and foreign particles enter the engine in different ways. They could have been left over from engine assembly or passed through filters or breathers. They could get into the oil and from there into the bearings. These may be metal particles left over from regrinding parts or formed during normal engine wear. Abrasive powder particles sometimes remain on engine components after repair, especially when the components have not been thoroughly cleaned. Whatever the source of the contamination, these foreign particles are pressed into the soft bearing material and are easy to detect. Large particles scratch the bearing and shaft. The best prevention for this type of bearing damage is to thoroughly clean all parts and keep everything spotlessly clean during engine assembly. Frequent and regular replacement of engine oil and filter will also prevent premature bearing wear.
5. Lack of lubrication can occur due to a number of interrelated reasons. It can be caused by too high a temperature (the oil loses viscosity, meaning its layer becomes thinner), overload (oil is squeezed from the bearing surface) and oil leaks or discharges (due to excessive bearing clearances, worn oil carrier). Blocked lubrication channels (usually due to misaligned lubrication holes in the bearing shell) also lead to lack of oil and bearing damage. If the bearing failure is caused by a lack of lubrication, the surface of the bearing shell is heavily worn.
6. Driving style can also affect bearing life. Full throttle, low speed, and engine overload will place a very high load on the bearings, causing the lubricant layer to be squeezed off the surface of the bearings. In addition, such a load causes the liners to bend, which leads to the appearance of small cracks. Eventually, the bearing shell breaks into pieces and flies out of the bearing. Short trips lead to bearing corrosion because the engine does not get hot enough to dissipate compressed water vapor and corrosive gases, which then dissolve in the engine oil, forming acid and sludge. When the acid gets into the bearings with oil, it causes corrosion of the bearing shell.
7. Installing the wrong size bearing shell will also cause it to fail. Too large liners leave insufficient lubrication clearance in the bearing, resulting in insufficient lubrication. In increased bearing working clearance (if small inserts are installed) dirt and foreign particles get in more easily.