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, connecting rod main bearing caps and their caps, lay them out on a clean surface in the same order as they are 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 the shaft journal. This cause is 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.
Insufficient lubrication has several interrelated causes. Excessive heat (which causes the oil to thin), overload (which causes the oil to be squeezed out of the bearing), oil leakage or blowout (due to excessive bearing clearance, worn oil pump, or high engine speeds) can all cause insufficient lubrication. Blocked oil passages, usually caused by misalignment of the oil bore when the bearing is assembled, also impair bearing lubrication and cause bearing failure. When bearing failure is due to insufficient lubrication, the bearing material is rubbed or squeezed out of the steel backing of the bearing. The temperature can rise so high that the steel backing turns blue from overheating.
The way the vehicle is driven can also affect the life of the bearing. Operating at low speeds in high gear (engine overload) places 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 failure). 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 can lead to its destruction. Strongly tightened bearings have a reduced oil clearance, which leads to a lack of lubrication.
Dirt or foreign particles will also damage the bearing.
The material was copied from the website mitsubishiman