Influence of the initial clearance on the peak stress in connecting-rod small ends

Abstract

The stress increase that is caused by the presence of an initial clearance within the small end of connecting rods for motorbike and car engines is investigated. Plane analytical and numerical modellings of the dry contact between the small-end and piston pin are adopted. Based upon a recent analytical result, a normalizing parameter is introduced, which allows the stress concentration factor at the small-end bore sides to be expressed as a function of a proper combination of the initial clearance between the small end and gudgeon pin, the applied load, and Young's modulus, for prescribed aspect ratios of the small end and hollow pin. Design diagrams summarizing the consequences of an initial clearance between the small-end bore and gudgeon pin on the eye peak stress are reported, which cover a wide range of geometries, clearances, and loadings. Selected comparisons between two-dimensional and three-dimensional models are carried out.