A three-dimensional finite-element model was developed for the diesel-engine piston. The model, which consists of a half section piston to accommodate the eccentric bowl in the piston head, is used to calculate operating temperatures and the corresponding thermal expansion, skirt flexibility, and operating stresses due to thermal and mechanical loads. The accuracy of the model was verified by using temperature data published in the literature, skirt thermal expansion data measured by the piston supplier, and skirt flexibility data measured in GMR.A technique to analyze the skirt-to-bore interaction was also developed. This includes calculations of the piston translation and rotation, skirt deformation, as well as the skirt-to-bore contact area and contact force under operating conditions. The analytical tool developed in this study was demonstrated to be useful for piston design.