THIS paper covers the work carried out by the Research and Standardization Committee of Cylinder Wear in gasoline engines. The report is divided into two sections, the first reviewing the work which has already been reported on in two issues of the Journal of the Institute.1 These issues are June, 1933, and August/September, 1934.
The experiments have been carried out on a number of single-cylinder units of 3⅜-in. bore, which can be fitted with either water-cooled or air-cooled barrels, and direct measurements of bore wear made by means of gages, piston-ring wear being measured by weighing. All readings of bore wear referred to in this paper were taken at the top of the ring track where wear is a maximum, and the readings are expressed in equivalent wear per 1000 miles of road operation.
The paper draws attention to the importance of corrosion under cold-running conditions. This importance was discovered through a systematic study of the effect of several different variables showing that below certain cylinder-wall temperatures there was a very rapid increase in wear. This study was confirmed by observations on the stained or pitted appearance of the cylinder walls and piston-rings of engines which had run at low cylinder-wall temperature; the presence of relatively large quantities of water in the lubricating oil under such operating conditions; the fact that the sudden increase in cylinder wear occurred when the cylinder-wall temperature approximated the calculated dew point or condensation temperature of the products of combustion at the pressure existing during the combustion cycle; the use of corrosion-resisting materials, namely, austenitic cast iron, for piston-rings and cylinders effects a considerable reduction in wear under low-temperature conditions.
The importance of thermostats in reducing cylinder-liner wear is shown, as is also the rapid increase in wear with increasing m.e.p. and cold-running conditions.
It is concluded from the result of the experiments on lubricants that pure medicinal paraffin gives inadequate protection from corrosion under cold-running conditions and that the presence of a fatty acid, or fatty oil, is necessary under such conditions. At high cylinder-wall temperatures representing abrasive conditions pure medicinal paraffin gave a very low rate of wear that was approximately the same as that of commercial lubricant, and various additions of fatty oils to the pure medicinal paraffin did not effect any marked improvement in wear.
The effect of increasing skirt clearance from 0.0058 in. to 0.0300 in. on the wear of the top piston-rings was quite marked, while the effect on cylinder wear was much less appreciable. The effect of radial piston-ring pressure was not of great importance, particularly within the range of pressure usually met with in practice. The effect of increasing piston-ring width from 3/64 in. to 3/16 in. at high cylinder-wall temperature, that is, under abrasive conditions was quite important. The rate of wear with the narrower rings being from 5 to 7 times greater than that with the wide rings.