Main and connecting rod bearings — inspection

1. Do not throw away the old main and connecting rod bearings after they have been replaced, inspecting them can provide valuable information regarding the condition of the engine.

2. Bearings fail due to lack of lubrication, dirt on them, motor overloads and corrosion. The cause of 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 with a specific crankshaft journal.

4. Dirt and foreign particles enter the engine in different ways. They may have been left after engine reassembly, or passed through filters or breathers. They could get into the oil and from there into the bearings. These can be metal particles left after regrinding parts or formed during normal engine wear. Grains of abrasive powder sometimes remain on engine components after repair, especially when the components have not been thoroughly cleaned. Whatever the source of 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 such bearing damage is to thoroughly clean all parts and keep everything spotlessly clean during engine reassembly. Frequent and regular engine oil and filter changes will also prevent premature bearing wear.

5. Lack of lubrication can occur for a variety of interrelated reasons. It can be caused by too high a temperature (oil loses viscosity, which means its layer becomes thinner), overload (oil is squeezed out of the bearing surface) and oil leaks or discharge (due to excessive bearing clearances, worn out oil carrier). Blocked lubrication channels (usually due to misaligned oil holes on the bearing shell) also lead to lack of oil and damage to the bearing. If the failure of the bearing is caused by a lack of lubrication, the bearing surface is badly worn.

6. Driving style can also affect bearing life. Full throttle, low speed, overloading the engine will give a very high load on the bearings, in which a layer of lubricant is squeezed out from the surface of the liners. 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 corrode the bearings because the engine does not get hot enough to disperse compressed water vapor and corrosive gases, which consequently dissolve in the engine oil, forming acid and sludge. If it gets on the bearings with oil, the acid causes corrosion of the bearing shell.

7. Installing the wrong size bearing shell will also cause it to break. Bushings that are too large leave insufficient lubrication clearance in the bearing, resulting in insufficient lubrication. In the increased working clearance of the bearing (if small inserts are installed) easier to get dirt and foreign particles.