What material is the crankshaft bearing of a car made of?
The automotive crankshaft bearing (also known as crankshaft bearing or large bearing) is a sliding bearing sleeve with a composite structure. It is mainly composed of a steel back and a wear-reducing alloy layer. This structure combines strength and wear resistance to adapt to the high-speed, high-pressure, and high-temperature working environment of the engine.
Main material composition
Steel back: Usually made of low-carbon steel or alloy steel, providing structural support and rigidity.
Wear-reducing alloy: In direct contact with the crankshaft, it serves the functions of reducing friction, bearing load, and dissipating heat. Common types include:
Babbitt alloy (tin-based or lead-based)
Characteristics: Good wear resistance and good adaptability
Application: Mostly used in gasoline engines with lower reinforcement levels
Copper-based alloy (such as lead bronze, copper-lead alloy)
Characteristics: High strength, high wear resistance, and high temperature resistance
Application: Suitable for diesel engines or high-load gasoline engines
Aluminum-based alloy (high-silver or low-silver aluminum-based)
Characteristics: Light weight, good heat dissipation, and excellent wear resistance
Application: Currently the most widely used in internal combustion engine crankshaft bearings. Additional Explanation
Aluminum-based alloys have become the mainstream choice due to their outstanding comprehensive performance, especially suitable for modern engines with high rotational speed and continuous operation.
Some high-end products will also undergo treatments such as tin plating and phosphating on the wear-resistant alloy surface to further optimize the frictional properties.
The crankshaft journals are usually used in pairs (upper and lower), installed between the crankshaft main journal and the cylinder block, relying on an oil film of about 0.005 millimeters to achieve fluid lubrication and prevent direct metal contact.
To view the specific material of the crankshaft journals of a particular vehicle, you can refer to the maintenance manual or query the compatible information through Autohome Crankshaft Journal.
The crankshaft journals of automobiles are key sliding bearing components in the engine. Their core functions can be summarized as follows:
Support and fix the crankshaft: Ensure that the crankshaft maintains a stable radial position during high-speed rotation, avoiding shaking or deviation.
Form an oil film for liquid lubrication: Establish an extremely thin (about 0.005 millimeters) oil film between the crankshaft journal and the journal, converting direct metal friction into fluid lubrication, significantly reducing wear.
Reduce friction and wear: Through the sleeve structure composed of wear-resistant materials such as babbitt alloy and copper-lead alloy, effectively reduce friction resistance and extend the engine's lifespan.
Heat dissipation and cooling: Utilize the circulation of engine oil to remove working heat, preventing the bearings from failing due to high temperature.
Axial positioning (for some types): The flanged crankshaft journals can also limit the axial movement of the crankshaft along the axis, ensuring the precise relative position of the moving parts.
If the lubrication is poor, the assembly is improper, or the engine oil contains impurities, it may cause the oil film to rupture, leading to serious faults such as burning the journal, seizing the shaft, etc., manifested as decreased oil pressure, abnormal noise, and reduced power. Therefore, regularly changing the engine oil and filters, and maintaining the vehicle according to the specifications, are of great significance for protecting the crankshaft bearings.
The failure of the crankshaft bearing in a car (commonly known as "wearing out the bearing" or "breaking the bearing") is one of the most serious mechanical failures of the engine. It is usually caused by the failure of lubrication, resulting in dry grinding, high-temperature sintering, and even seizing between the crankshaft journal and the bearing. In severe cases, it can even lead to the destruction of the engine.
Main manifestations:
Abnormal noise: The engine emits a dull "tang, tang" or "buzzing" metallic knocking sound, especially more pronounced when accelerating.
Oil pressure alarm: The oil pressure indicator light on the dashboard illuminates, and the oil pressure gauge shows a low reading.
Power loss: The engine's output power decreases, and acceleration becomes weak.
Excessive exhaust: Black smoke may be emitted.
High-temperature alarm: Abnormally high water temperature or oil temperature.
Unable to start or engine stalling: In extreme cases, the crankshaft and bearing are burned and stuck together, preventing the engine from rotating.
Common causes:
Lubrication system problems:
Insufficient oil pressure (oil pump wear, pressure limiting valve failure, oil circuit leakage).
Insufficient or deteriorated oil quantity (long-term lack of replacement, use of inferior oil).
Oil emulsification (coolant seeping into the oil pan, such as failure of the water-blocking ring of the cylinder liner).
Blocked oil passages (impurities, carbon deposits, metal shavings blocking the main oil passage or crankshaft oil holes).
Assembly and clearance problems:
Excessive or insufficient bearing clearance (affecting the formation of the oil film).
Incorrect bearing selection or installation.
Operation and usage habits:
Starting the engine at a high speed and under heavy load immediately after cold start.
Long-term overloading and high-speed driving.
Immediately stalling the engine after it gets hot, causing the oil film to be damaged.
Design or manufacturing defects:
Poor surface finish and material quality of the crankshaft or bearing.
Out-of-specification crankshaft journal roundness, deformation, etc.
Treatment suggestions:
Stop the vehicle immediately: Once suspected symptoms of bearing failure (such as abnormal noise, oil pressure alarm) occur, stop the vehicle immediately and do not continue driving. This is to avoid further damage.
Professional maintenance:
Replace the crankshaft main bearing (large bearing) and connecting rod bearing (small bearing).
Check if the crankshaft journal is scratched, oxidized, pulled, or deformed; if the damage is severe, it is necessary to "grind the shaft" or replace the crankshaft.
Clean the oil passage, replace the oil pump and filter, and repair leakage points in the cooling system.
Evaluate if it can be used further:
If it is a "minor bearing failure", after professional grinding repair and replacement of the new bearing, it may be used again.
If the crankshaft journal is severely worn, the crankshaft is deformed or broken, then it is necessary to replace the crankshaft. It is not recommended to continue using the old part.
Preventive measures:
Regularly check and replace the oil and filter that meet specifications.
Before driving, confirm that the oil level is within the normal range (the middle scale of the dipstick).
Avoid high-speed or heavy-load operation immediately after cold start.
Preheat the engine to a water temperature above 40°C before starting in winter.
Pay attention to the oil condition: If there is emulsification (white color, much foam), decreased viscosity, or a gasoline smell, immediately repair it.
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