What Engine bearings Failure types are known and what are their causes?
Typical bearing shell failure causes are below:
Normal wear
Observed small, hairline marks on bearing surface, with relatively few signs of foreign particles are normal signs of wear.
Fatigue (overload)
Worn and degraded areas located only on the top bearing in the connecting rods, or on the lower bearing in the block are a sign of fatigue. Excessive loads caused by detonation due to advanced ignition, poor quality fuel, and excessive compression may lead to this type of damage. Lugging the engine when pulling heavy loads can also contribute to bearing fatigue.
Dirt embedment
Solid particles embedment could be observed on the bearing shell surface. Inadequate maintenance because of infrequent oil changes and lack of maintenance to the air filter contributes sand and dust particles into the oil. Unclean conditions when assembling an engine during an overhaul will also result in bearing damage of this type.
Misalignment ( Connecting Rod )
This type of wear could be judged by highly worn one side of the shell. Misalignment may be caused by a distorted bearing bore, bent connecting rod, or combustion problems causing irregular side loading on the piston and connecting rod.
Lack of oil
A bearing suffering from excessive friction and fusing caused by lack of oil has deep and wide tear marks with signs of overheating. Some of the causes of lubrication failure are a blocked oil filter cartridge, broken oil line, failure of the oil pump, or excessively low oil level in the working engine.
Cavitation
This bearing shows signs of erosion caused by noxious acids in the oil. Some of the causes are an extreme flow of gases caused by blowby, fuel pump leaking fuel into the crankcase, oil contamination by coolant, and excessive operating temperatures.
Distorted crankcase
Depending on the type of block distortion, the bearing wear will be most extreme on the tops of the outer bearings and the bottoms of the center bearings, or the tops of the center bearings and the bottoms of the outer bearings.
The block straightness must be checked and align honed or bored to correct this problem.
Distorted Crankshaft
Bearing failure which produces severe wear on both the upper and lower halves of the bearing are usually caused by excessive distortion of the crankshaft. This may be a result of unusually high loading conditions and excessive speed. A bent crankshaft will also produce this type of wear.
