Why are engine plain bearings damaged?

- Oct 08, 2018 -

1, mechanical damage refers to the alloy surface of the bearing of different degrees of groove marks, serious when the contact surface metal stripping and a large area of disorderly scratches; in general, contact surface damage and ablation phenomena exist simultaneously. The main cause of bearing mechanical damage is that the bearing surface is difficult to form oil film or oil film is seriously damaged. 


2, in the cylinder pressure impact load of the repeated action, the surface layer of plastic deformation and cold-hardening, local loss of deformation ability, gradually formed the pattern and continue to expand, and then with the peeling of the debris, in the surface layer formed Cavity. When cavitation occurs in the general bush, the pits are first appeared, and then the pits gradually expand and cause the interfacial cracking of the alloy layer, and the crack expands along the parallel direction of the interface until peeling off. The main reason for the cavitation erosion of sliding bearings is that the sudden change of the cross section of the oil groove and the oil hole causes the oil flow to be strongly disturbed, and the bubbles are formed in the vacuum area of the oil flow disturbance, and then the bubbles are collapse due to the pressure rise and Cavitation. Cavitation usually occurs in the high load area of the bearing, such as on the lower bearing of the crankshaft main bearing. 


3, The bearing fatigue pitting refers to, because the engine overload work, make the bearing work overheating and the bearing clearance is too large, resulting in the central bearing fatigue damage, fatigue pitting or fatigue fall off. Most of this damage is caused by overloading, excessive bearing clearance, or the fact that the lubricant is not clean and mixed with foreign objects. therefore, the use should be careful to avoid the bearing overload work should not be too low or too high speed, the engine to stabilize the idle speed, to ensure normal bearing clearance, to prevent engine speed too high or too low, check and adjust the cooling system work, to ensure that the engine operating temperature is Appropriate. 


4, Plain bearing alloy corrosion is generally the area for the lubricating oil is not pure, lubricating oil in the chemical impurities (acidic oxides, etc.) so that the bearing alloy oxidation and the formation of acidic substances, causing the bearing alloy part off, the formation of irregular micro-hole or small pits.The main cause of corrosion of bearing alloy is improper selection of lubricant, poor corrosion resistance of bearing material, or rough engine, high temperature and so On. 


5, the shaft neck and the bearing friction pair has the small convex metal surface direct contact, forms the local high temperature, in the lubrication insufficiency, the cooling bad condition, causes the bearing alloy blackening or the partial melting. This fault is often caused by tight fitting of the shaft neck with the bearing, and it is easy to burn out the bearings due to insufficient lubricant pressure. Regular inspection and maintenance of sliding bearings is needed.