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PISTON-ring scuffing occurs most frequently during the break-in period and has been a problem to both the automobile and ring producers, for some time. Ring coatings have been under development for several years and their general adoption by nearly all automobile companies indicates both the need for them and their effectiveness. The coatings fall into two general classes, chemical and metallic. The chemical are: Ferrox, an iron oxide; Granoseal, an iron-manganese phosphate; Graphitox and Grafotox, a zinc-iron phosphate with colloidal graphite; and Surfide, ferrous sulphide. The metallic coating is of electrolytically deposited tin. Careful tests under accelerated wear or scuffing conditions on newly finished surfaces showed that untreated rings produced twice the wear that occurred on the coated rings when only the compression rings were coated. The difference in wear was even greater when both compression and oil rings were coated properly.

IN analyzing causes of cylinder-bore wear it is found that they fall generally into one of the following classifications: (1) Abrasion - wear due to foreign particles in the oil film. (2) Erosion - wear due to metal contact between the pistons or rings and the cylinder bore. (3) Corrosion - oxidization or chemical action of the cylinder wall by the products of combustion. Although these classifications place the three main factors in the approximate order of their importance, the conditions of operation, the design of the engine, the design of the air cleaner, the piston and ring equipment, or the lubricating oil used, may change the order completely. Four ways are described for abrasives to get into the engine, and three design factors are mentioned that will reduce cylinder wear in the presence of dust. Keeping the dirt out, however, is stated to be the only real solution, and air cleaners are recommended as the best method.