Crankshaft bearing failures are caused by insufficient lubrication, dirt and debris, engine overload, and corrosion. Regardless of the cause that caused the destruction of the bearings, it should be eliminated before the final assembly of the engine in order to avoid repeated 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 spread out on a clean surface in the same order in which they were installed on the engine. This will allow you to install the appropriate crankshaft bearing, in which the bearing has undergone increased wear.
Dirt and foreign particles enter the engine for various reasons: during the assembly process, through filters or the crankcase ventilation system, with oil. Contaminants often include metal chips from machining engine parts or from wear and tear during normal engine operation. Sometimes there are residues of abrasive materials in the dirt after lapping and grinding, especially after carelessly carried out 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 scuffing on the surfaces of both the bearing and the crankshaft journals. The best way to eliminate the cause of this wear is to thoroughly flush 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 often.
Insufficient engine lubrication can be due to a number of interrelated reasons. These include excessive engine overheating (causes oil to thin), overload (cause oil to be squeezed out of the bearing surface) and pressure drop due to leakage (ejection) oils (due to increased clearances in the bearings, wear of the oil pump, high crankshaft speed). The cause of accelerated wear of the crankshaft bearings is also the blockage of the oil channels, usually due to misalignment of the lubrication holes in the bearing and its housing parts, which causes insufficient lubrication and failure. If insufficient lubrication is the cause of failure, the bearing coating material will be chafed or extruded from the steel base. The temperature rises so much that the steel base of the bearing is painted blue due to overheating, the possibility of deformation of the bearing caps and connecting rod cap bolts is not ruled out.
The durability of crankshaft bearings largely depends on driving skills and driving conditions. Bearings experience increased stress when driving at wide open throttle, during long trips at low speeds and slip. Under increased loads, the oil film is squeezed out, the bearings experience bending deformations, in which microcracks form (fatigue wear). As a rule, the bearing coating comes off the steel base in the form of small particles. Short journeys can lead to corrosive wear of bearings, as condensates and corrosive gases accumulate due to insufficient warm-up. These components accumulate in the oil, causing the formation of acids and insoluble deposits. Such oil, entering the bearings, causes them to corrode under the influence of acids, as a result of which they are destroyed and fail.
Bearing failure can also be caused by improper installation during engine assembly. Too tight a fit causes insufficient lubrication clearance and poor lubricant penetration. Dirt and foreign particles trapped under the underside of the bearing cause uneven fit and premature failure.