bearings, and few studies have been conducted on small-end bearing test rigs. The current connecting rod-small-end bearing test rig mainly simulates the reciprocating motion of the piston in operation through a driven motor, providing a defined reciprocating motion to the tested part, whereas the pumping lubrication effect is simulated by a load applied to the piston pin via a hydraulic system. A swing piston pin and two loadable metal half-rings were designed by [PERSON] et al. [5] to simulate the oscillation of the piston pin relative to the bushing, and the load was imposed by the bushing. The test rig was used to measure parameters such as the rotation speed, loading pressure, and friction torque during the experiment. [PERSON] et al. [2,6] developed a bushing structure based on this concept and analyzed the effects of various parameters on the increase in friction, temperature, and other characteristics. The motion of the piston pin or bushing in the above test rigs is based on the assumption of an idealized motion while ignoring the fact that in a real engine, the relative motion is determined by uncertain frictional forces, which are determined by the lubrication conditions. Therefore, it is difficult for the current test rigs to accurately reflect the friction state of the piston pin, and these rigs cannot fully reveal the lubrication and kinetic characteristics of the piston pin in real reciprocating engines. The abovementioned studies have not been combined with a multifactor theoretical analysis of EHD lubrication. As the small-end bearing of the connecting rod falls under the category of journal bearings, the lubrication mechanism of its pair interface follows the hydrodynamic lubrication law. Small-end bearings can withstand a large load impact and large elastic deformation while exhibiting a low linear velocity during operation compared with large-end bearings or main bearings. These characteristics have a significant impact on hydrodynamic lubrication and asperity contact; therefore, they must be considered during the calculation and analysis. After [PERSON] and [PERSON] applied the mean Reynolds equation to lubrication analysis, a number of theoretical studies considered the microscopic morphology between the two surfaces, the gap and influence of the lubricant [11,12], and the lubricant viscosity-pressure and viscosity-temperature effects [12, 13, 14], which improved the accuracy of the calculations. [PERSON] [15] conducted an analysis of piston pin multi-body dynamics and examined the effects of different models on the calculations of lubrication characteristics, as well as the effects of piston pin stiffness and pin boss shape on lubrication characteristics. Using a small-end bearing EHD model, [PERSON] et al. [16] compared and analyzed the effect of oil film lubrication on stress distribution to establish the importance of considering oil film lubrication in mechanical analysis. [PERSON] et al. [17] established a multi-body dynamics model coupled with the EHD property of fully floating piston pin bearings to reveal the mechanism of friction reduction and scuffing resistance of these bearings. Furthermore, various studies have been conducted by different researchers regarding the factors affecting lubrication characteristics. [PERSON] et al. [18] analyzed small-end bearing clearance as a key parameter in multi-body dynamics modeling and lubrication performance analysis. [PERSON] et al. [19] demonstrated that the clearance between the piston pin and bushing must be considered when analyzing the reliability of connecting rods and generated a normalized parameter that includes the initial clearance and geometry to predict the peak stress within the pin boss. The effect of surface micromorphology on the Stribeck curve was examined by [PERSON] et al. [20] to improve the lubrication and tribological characteristics of the small-end bearing by controlling the surface properties. [PERSON] et al.