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There are many parts in the engine with high speed movement and high precision. The installation accuracy of these parts is directly related to the performance of the engine, and the engine bearing bush is one of the key parts.
There are many parts in the engine with high speed movement and high precision. The installation accuracy of these parts is directly related to the performance of the engine, and the engine bearing bush is one of the key parts.
The role of bearing bush
The bearing bush between the crankshaft spindle neck and the support seat is called the main bearing bush (big tile), and the bearing bush between the big end of the connecting rod and the crankshaft connecting rod journal is called the connecting rod bearing bush (small tile). The bearing bush is made of thin-walled steel back, and the surface is cast with wear-resistant alloy layer. The alloy layer has the characteristics of soft quality, small friction resistance and not easy to wear. There is a lubricating film between the journal and the bearing bush to reduce wear on the surface of the mating parts.
When the engine is working normally, the wear degree of the bearing bush is very small, but when the lubrication condition inside the engine becomes worse, or when mechanical failure occurs, it will cause abnormal wear of the bearing bush.
Bearing bush failure forms and causes
1.Burning tile holding shaft
Fault phenomenon: the poor lubrication between bearing bush and journal leads to dry wear, the high temperature of the contact surface causes the melting and sintering of bearing bush, and the journal is locked, so that the engine cannot run.
Cause of failure:
1.Bearing bush clearance is too large. Bearing bush normal wear to a certain extent, and the gap between the journal becomes larger, resulting in oil pressure relief and not very good terrain oil film, bearing bush between the oil supply is insufficient.
2.The high temperature. Cooling system failure or lack of coolant, resulting in long-term high-temperature engine operation, oil viscosity decline, can not form an oil film between the bearing bush and the journal.
3.Improper maintenance. Do not replace the oil for a long time, the use of fake oil or oil additives, resulting in the bearing bush can not be lubricated.
2.Peeling of the alloy layer
Fault phenomenon: bearing bush surface coated with anti-friction alloy coating, can reduce the coefficient of friction, reduce wear. If the alloy layer is peeled off, the gap between the bearing bush and the journal will become larger, eventually leading to the failure of the burning tile holding shaft.
Cause of failure:
1.Corrosion. While lubricating the bearing bush, the oil will also oxidize and corrosion the alloy surface of the bearing bush, resulting in the spalling of the metal on the surface of the alloy layer. If poor quality oil is used, the oxidation corrosion of the alloy layer will be accelerated.
2.Thermal fatigue. If the engine runs for a long time at low speed and under heavy load, the alloy layer of the bearing bush will flake off because of overheating.
3.Scratches from impurities. Dust, metal particles random oil into the bearing bush and journal, scratch the alloy layer, resulting in the peeling of the alloy layer.
3.Abnormal wear
Fault phenomenon: During engine operation, some moving parts fail, resulting in abnormal wear of bearing bush.
Cause of failure:
1.The link bends. Due to some reasons, such as water in the combustor, the connecting rod is bent due to excessive load, and the surface of the bearing bush alloy layer is seriously worn due to excessive force.
2.Bearing cover bolts are too tight or too loose. Too large or too small tightening torque will cause abnormal wear of bearing bush.
Key technical points of bearing bush assembly
No matter what the cause of engine overhaul, bearing bush needs to be replaced in accordance with technical requirements. The bearing bush matching with the engine model should be selected, and the following technical points need to be paid attention to when assembling the bearing bush.
1.Clean bearing bush and bearing housing to ensure no dust and impurities.
2.The back of the bearing bush is coated with clean lubricating oil and placed on the bearing seat/bearing cover. The positioning lip of the bearing bush corresponds to the corresponding groove of the bearing seat and bearing cover. If the positioning lip and groove do not match, usually the upper and lower shingles installed in reverse.
3.The bearing cover and bearing seat are pieced together on the journal, and the fixing bolts are tightened according to the specified torque to ensure the clearance between the bearing bush and the journal.
4.When installing the bearing bush, pay attention to whether the oil hole of the bearing bush is aligned with the oil hole on the bearing seat.
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