Checking main and connecting rod bearings (Mazda Capella GE)

Causes of bearing wear

Although main and connecting rod bearings must be replaced during a major engine overhaul, old bearings should be kept in their original location for careful inspection, as wear marks on these parts can help restore the overall condition of the engine.

Causes of crankshaft bearing failure include insufficient lubrication, the presence of 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.

(The original article is on: «MAZBOOK.RU»)

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, through the oil.

Often, contaminants contain metal particles from mechanical processing of engine parts, or as a result of wear during normal engine operation. Sometimes the contamination contains residues of abrasive materials after lapping and grinding work, especially if there is insufficient rinsing 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 will cause 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 blocked oil passages, usually due to misalignment of lubrication holes in the bearing and its housing components, which leads to insufficient lubrication and failure. When failure is caused by insufficient lubrication, the bearing coating material is wiped or squeezed out of the steel base. The temperature rises to such a level that due to overheating the steel base of the bearing is discoloured blue, and the possibility of deformation of the bearing caps and connecting rod bolts cannot be ruled out.



The durability of crankshaft bearings also depends significantly on driving skills and the nature of the movement. Bearings experience increased loads when driving with the throttle fully open, during long-term driving 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 is torn off from the steel base in the form of small particles. Short-distance travel can cause corrosive wear of bearings, as insufficient warming prevents the condensed moisture and gases that cause corrosion from being removed. These components accumulate in the oil, causing the formation of acids and insoluble precipitates. As oil reaches the bearings, they become corroded by the acids, causing them to deteriorate and fail.

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