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

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