Bearing damage is caused by lack of lubrication, dirt or foreign particles, engine overload and corrosion. Regardless of why the bearings are damaged, the cause must be corrected before the engine is assembled.
When checking bearings, remove them from the cylinder block, main bearing caps, connecting rods and their caps, and lay them out on a clean surface in the same order in which they are located in the engine. This will allow you to determine the cause of damage for each specific shaft journal.
Damaged bearings
Dirt and foreign particles are pressed into the soft material of the liners. Large particles cannot be pressed in completely, they will scratch the bearing and shaft journal. This cause can be eliminated by thoroughly cleaning all parts and keeping them clean during assembly. It is also recommended to change the oil and oil filter in a timely manner.
Lack of lubrication has several interrelated causes. Excessive heat (which makes the oil liquid), overload (causes oil to be squeezed out of the bearing), oil leak or spill (due to too much bearing clearance, worn oil pump or high engine speed) may lead to a lack of lubrication. Blockage of oil passages, usually caused by misalignment of oil holes during bearing assembly, also disrupts bearing lubrication and leads to bearing failure. When bearing failure is caused by lack of lubrication, the bearing material is rubbed or squeezed out of the steel bearing shell. The temperature can rise so high that the steel base will turn blue from overheating.
The way you drive your vehicle can also affect bearing life. Operating at low revs in high gear (engine overload) leads to very high loads on the bearing and causes the oil film to be squeezed out. These loads cause the bearings to bend, which leads to surface cracking (fatigue failures). Eventually, the bearing material is chipped and carried away from the steel base. Driving short distances causes bearing corrosion because the engine does not warm up enough to remove condensed water and corrosive gases. They accumulate in the oil, forming acids and sediment. When oil gets into the bearings, the acid causes corrosion of the bearing material.
Incorrect installation of the bearing may result in its destruction. Over tightened bearings have reduced oil clearance, resulting in insufficient lubrication.
Dirt or foreign particles will also damage the bearing.