Inspection of main bearings and connecting rod bearings

Reasons for bearing wear

Although the main and connecting rod bearings must be replaced during engine overhauls, old bearings should be stored at the place of their installation for a thorough inspection, since wear marks on these parts will restore the general condition of the engine.

Causes of failure of crankshaft bearings are insufficient lubrication, the presence of dirt and foreign particles, 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 the bearings, they must be removed from the 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, through the oil.

Contaminants often contain metal particles from the machining of engine parts, or due to wear during normal engine operation. Sometimes there are residues of abrasive materials in the dirt after lapping and grinding, especially with insufficient 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 will not be able to 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. When insufficient lubrication is the cause of failure, the bearing coating material is chafed or extruded from the steel base. The temperature rises to such a level that overheating causes the steel base of the bearing to become blue in color, and the possibility of deformation of the bearing caps and connecting rod bolts is not ruled out.

The durability of crankshaft bearings is also significantly dependent on driving skills and the nature of movement. Bearings experience increased loads when driving at wide open throttle, driving for a long time at low speeds, and slipping. Under increased loads, the oil film is squeezed out, the bearings experience bending deformations, in which microcracks form (fatigue wear). As a rule, there is a separation of the bearing coating from the steel base in the form of small particles. Short trips can cause corrosive wear of bearings, because due to insufficient warm-up, condensed moisture and corrosive gases do not have time to escape. These components accumulate in the oil, causing the formation of acids and insoluble deposits. As oil enters the bearings, they corrode under the influence of acids, causing their destruction and failure.

Bearing failure can also be caused by improper installation during engine assembly. Too tight fit causes insufficient lubrication clearance and poor lubricant penetration. Dirt and foreign particles trapped under the back of the bearing cause uneven fit and premature failure.