Piston Assemblies for Road Transport Oil Engines

Abstract

After reviewing the more usual types of piston failures such as breakage, seizure, ring sticking, land breakage, land scuffing, and groove destruction, means are suggested for their avoidance. There follows a consideration of the limiting factors of piston life, as indicated by the oil consumption of the engine. Dangers of overscraping new engines are emphasized and a method of retaining a minimum consumption over a long life is suggested. Examination of the rates of wear of the various components of the piston assembly leads to the conclusion that the top compression ring is the weakest point. Service test results with different piston ring materials are given and improved materials are suggested. Chromium-plated piston rings give the best results and are recommended for use as the upper compression ring. Finally, suggestions are given for designing the successful oil engine piston with a strong recommendation for the use of 12 per cent silicon alloy material and an adequate path for heat flow from the piston crown to the ring zone. Gudgeon-pin design is an important feature and design formulae are given. In summarizing, a model piston ring layout is given in detail.