Bearing damage is caused by lack of lubrication, dirt or foreign particles, motor overload and corrosion. Regardless of why the bearings are damaged, this cause must be corrected before the engine is reassembled.
When checking the bearings, remove them from the cylinder block, main bearing caps, connecting rods and their caps, lay them on a clean surface in the same order as they are in the engine. This will 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 fully pressed in, they will scratch the bearing and the shaft journal. This cause is eliminated by thorough cleaning of 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. Excess heat (which makes oil liquid), overload (causes oil to be squeezed out of the bearing), oil leakage or ejection (due to too much bearing clearance, worn oil pump or high engine speed) can lead to lack of lubrication. Blockage of oil passages, usually caused by misalignment of oil holes during bearing assembly, also interferes with bearing lubrication and leads to bearing failure. When bearing failure is caused by lack of lubrication, the bearing material is worn or extruded from the steel backing of the bushing. The temperature can rise so much that the steel base turns blue from overheating.
Vehicle driving patterns can also affect bearing life Low RPM operation 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, resulting in surface cracking (fatigue damage). Eventually, the bearing material will chip and be carried away from the steel base. Driving for short distances causes corrosion of the bearings, as the engine does not warm up enough to remove condensed water and corrosive gases. They accumulate in the oil, forming acids and sludge. When oil enters the bearings, the acid will corrode the bearing material.
Incorrect installation of the bearing can lead to its destruction. Heavily tightened bearings have a reduced oil clearance resulting in a lack of lubrication.
Dirt or foreign particles will also destroy the bearing.