What is the automotive connecting rod bearing?
The crankshaft pin (commonly known as "small pin") is a crucial sliding bearing component in an engine. It is installed between the large end of the connecting rod and the crankshaft connecting rod journal, serving to connect the piston, connecting rod and crankshaft, and facilitating power transmission and motion conversion. Core function
Reduce friction: By using high-maintenance-resistant materials, the sliding friction between the connecting rod and the crankshaft is reduced.
Support and positioning: Ensure that the connecting rod rotates stably around the crankshaft during high-speed oscillation.
Heat dissipation: Convey the heat generated by friction to the large head of the connecting rod to prevent local overheating.
Fuel supply and lubrication: Some connecting rod journals are designed with oil grooves and oil holes, which supply oil to the piston inner wall to cool the piston.
Structural features
Material composition: Usually composed of steel back + wear-reducing alloy layer (such as Babbitt alloy, high tin-aluminum-based alloy, lead bronze, etc.).
Thickness: The steel back is approximately 1–3mm, and the wear-reducing layer is approximately 0.3–0.7mm.
Split design: It is divided into upper and lower journals, and the installation direction and marking must be noted during installation.
Positioning structure: There are positioning protrusions or notches to prevent rotation or incorrect installation.
Common alternative names and distinctions
"Small journal": Named because the connecting rod journal is thinner than the main journal (the "large journal"), and it is smaller in size.
Difference from main journal:
Main journal (large journal): Supports the crankshaft journal and is fixed on the cylinder block. The structure often has oil holes and grooves for oil supply, used for stable support.
Connecting rod journal (small journal): Follows the reciprocating oscillation of the connecting rod, with a simpler structure. Some high-speed engines have a coating to enhance wear resistance.
Fault manifestations
Excessive clearance: Decreased oil pressure and "knocking cylinder" sound.
Insufficient clearance: Accelerated wear, and in severe cases, it may cause "crankshaft locking".
Abnormal noise: The fault of connecting rod journal is mostly manifested as a clear "tapping" sound, especially more obvious during sudden acceleration.
Maintenance suggestions
When replacing connecting rod journals, it is necessary to use original or matching specifications of genuine journals.
Installation must strictly follow the torque requirements to tighten the connecting rod bolts, and ensure the assembly specifications such as the direction of the journal, marking, and the arrow direction of the piston towards the timing gear.
During daily maintenance, pay attention to the quality of the oil and the replacement cycle, as inferior oil will accelerate the wear of the journal.
Car connecting rod journals (commonly known as "small journals") are key sliding bearing components in the engine, installed between the large head of the connecting rod and the crankshaft journal. Their core functions can be summarized as follows:
Reduce friction and wear: Through the wear-reducing alloy layer (such as white alloy, aluminum-based alloy, etc.), the direct friction between the large head of the connecting rod and the crankshaft journal is reduced, protecting both from excessive wear.
Support and positioning: As a sliding bearing, it supports the crankshaft journal, ensuring the stable connection between the connecting rod and the crankshaft, maintaining the precise motion trajectory.
Transmit power: Transfers the gas pressure and reciprocating inertia force borne by the piston to the crankshaft, achieving the conversion from piston linear motion to crankshaft rotational motion.
Lubrication and heat dissipation:
The oil grooves and oil holes on the journal precisely convey the oil, forming a stable oil film, achieving lubrication;
The thin steel back conducts the friction-generated heat to the large head of the connecting rod, assisting in heat dissipation, preventing local overheating.
Extend service life: Through wear-resistant design and reasonable assembly, reduce journal wear, and improve the overall durability of the engine.
Connecting rod journals are usually divided into upper and lower journals. The upper journal has oil grooves and oil holes for supplying oil to the piston inner cavity for cooling; the lower journal has no oil grooves and mainly assumes the supporting role. During installation, pay attention to the direction of the positioning protrusions and torque standards, otherwise, it is prone to cause abnormal noise, burning of the journal, or even crankshaft locking.
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