Conventionally, the engines are calibrated under the assumption that engines will be made exactly to the prints, and all the engines from the production line will be identical. However, engine-to-engine variations do exist which will affect the engine performances, and part-to-part variations, i.e., the tolerance, is an important factor leading to engine-to-engine variations. There are researches conducted on the influence of dimensional tolerances on engine performance, however, the impact of straightness, which is an important geometric tolerance, on lubrication is an unsolved issue. This study presents a systematic method to model the straightness and to analyze its effects on the friction loss. The bearing model is built based on elastohydrodynamic (EHD) theory. Meanwhile a novel modeling method to represent the straightness in three-dimensional space is proposed. Then the meta-model with straightness as inputs and friction loss as outputs is built based on Kriging interpolation theory. Genetic algorithm (GA) is utilized to determine the straightness configurations for the best and worst lubricating conditions. Results show that the straightness can benefit the bearing lubrication under some configurations, and may increase the friction power loss under other configurations. It is also shown that the degree of friction variation is determined by the curvature of the straightness.