Causes of crankshaft bearing failure include insufficient lubrication, dirt and foreign particles, engine overload and corrosion. Regardless of the cause of bearing failure, it should be corrected before final engine assembly to avoid further damage to these parts.
When checking bearings, they must be removed from their seats (from the cylinder block, crankshaft main bearing caps, connecting rod caps and connecting rods) and lay them out on a clean surface in the same order in which they were installed on the engine. This will allow the installation of a suitable crankshaft support where the bearing has been subjected to increased wear.
Dirt and foreign particles enter the engine for various reasons: during assembly, through filters or the crankcase ventilation system, and with the oil. Contaminants often include metal shavings formed during machining of engine parts or due to wear during normal engine operation. Sometimes the dirt contains residues of abrasive materials from lapping and grinding work, especially after careless washing and cleaning. Regardless of the cause of origin, foreign contaminants are usually embedded in the soft alloy of the bearing and are easily visible. Large particles cannot penetrate the bearing and lead to scratches and scuffs on the surfaces of both the bearing and the crankshaft journals. The best way to eliminate the cause of such wear is to thoroughly clean the parts and maintain impeccable cleanliness during the engine assembly process. To prevent premature wear, it is also recommended to change the oil and filters more frequently.
Insufficient engine lubrication can be caused by a number of interrelated reasons. These include excessive engine overheating (causes oil liquefaction), overloads (cause oil to be squeezed out from the surface of the bearings) and a decrease in pressure due to oil leakage (ejection) (due to increased clearances in bearings, wear of the oil pump, high crankshaft speed). Another cause of accelerated wear of crankshaft bearings is blockage of oil passages, usually due to misalignment of lubrication holes in the bearing and its housing components, which leads to insufficient lubrication and failure. If the cause of failure is insufficient lubrication, the bearing coating material is wiped or squeezed out from the steel base. The temperature rises so much that the steel base of the bearing turns blue due to overheating, and the possibility of deformation of the bearing caps and connecting rod cap bolts cannot be ruled out.
The durability of crankshaft bearings largely depends on driving skills and driving conditions. Bearings experience increased loads when driving with the throttle fully open, during long trips at low speeds and when slipping. Under increased loads, the oil film is squeezed out, and the bearings experience bending deformations, which cause microcracks to form (fatigue wear). Typically, the bearing coating breaks away from the steel base in the form of small particles. Short-distance travel can cause corrosive wear of bearings, as insufficient warm-up causes condensation and gases to accumulate, causing corrosion. These components accumulate in the oil, causing the formation of acids and insoluble precipitates. This oil, when applied to bearings, causes them to corrode under the influence of acids, resulting in their destruction and failure.
Bearing failure can also be caused by improper installation during engine assembly. Too tight a fit will result in insufficient clearance for lubrication and poor lubricant penetration. Dirt and foreign particles trapped under the back of the bearing cause uneven contact and premature failure.