‘Zero-wear’ of piston skirt surface topography

An analysis of the surfaces of a large number of piston skirts after engine operating was performed. Changes of piston skirts surfaces under the “zero-wear” condition were analysed. The amplitude of worn piston skirt surfaces decreased, the ordinate distribution became asymmetric, summit density increased and lay direction changed from circumferential to axial during wear. The relationship between microgeometry parameters was studied using correlation and regression analysis. It follows from the study that one can fairly precisely describe a piston skirt surface topography using the following parameters: Sq, SSk (or Sp/St), Str and Sdq. The parameters St±3σ, Sku, Sds, SSc and PΔax/PΔay are recommended for detailed description. It was decided to determine the local wear of piston skirts based on the changes in amplitude parameters. An increase in the initial surface height caused and increase in piston skirt wear. The local linear wear of piston skirts was bigger on the thrust side than on the anti-thrust side of the cylinder.