From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Cylinder bore wear, its causes, and related experiments.
| Identifier | ExFiles\Box 132\5\ scan0127 | |
| Date | 1st January 1939 | |
| 18 DISCUSSION ON CYLINDER BORE WEAR advantages which the author claimed. When it was discovered in this country that phosphorus seemed to be what was needed, they endeavoured again to get cylinder blocks containing phosphorus. The foundries, however, were unable to supply proper castings; they were blown, porous, and thoroughly unsatisfactory. Manufacturers were reduced, therefore, to fitting new engines with liners containing about 1 per cent of phosphorus. Though the organization with which he was associated could not carry out mass experiments to the same extent as the authors, it was in one respect perhaps in a more fortunate position in that a very large number of engines were being operated by a single concern with whom the closest touch was maintained. Experiments had shown that hardness in itself was quite useless in avoiding cylinder wear. At first the high-phosphorus liners were hardened, but more recently it had been decided to eliminate the hardening as an unnecessary cost. The difference in wear between the hardened and unhardened liners had proved to be negligible; they were running 8,000-10,000 miles per 0·001 inch wear on city transport services, which compared favourably with the author's figure for his trucks. Those engines were, of course, much bigger, but the service which they operated was rather arduous. The worst type of vehicle from the point of view of cylinder wear was the tank wagon, which ran from garage to garage, at each of which its engine was stopped because of fire risk. The next worst offenders were the city omnibus services, in which the engines were always starting and stopping, while the best were those on long-distance runs where the engine remained hot. Thermostats were by no means an unmixed blessing. On vehicles running under fairly steady conditions the thermostat corrugations filled up with time, so that the apparatus did not shut when the engine cooled off again. Like Wing Commander Cave-Browne-Cave he did not see how a small vacuum in the crankcase could be of any service. It could not prevent the crankcase accumulating 100 per cent of the blow-by gases, which would not be taken away with any certainty unless there was a steady flow of fresh air through the crankcase. He had carried out a great number of tests of considerable duration on lubricating oils and various fuels on an air-cooled engine with a high cylinder temperature. Some engines were run more or less continuously for several thousand hours, and under those conditions the cylinder wear was negligible—about 0·004 inch after running for 10,000 hours. The rate of wear was about the same when running on alcohol, paraffin, petrol, or the natural gas available in the neighbourhood. It was not then CYLINDER BORE WEAR Plate 1 realized, however, that the engines were being run under the best possible conditions for avoiding cylinder wear. To run a fleet of cars non-stop for thousands of miles round the country gave no idea of the wear and tear of cylinders under ordinary service conditions. It was the combination of corrosion, which occurred under cold conditions, with mechanical wear, that gave rise to trouble. Continuous running gave a measure of the real abrasive wear. Service running gave the combined effects of wear and corrosion. If the cylinder head of any internal combustion engine were removed after a run, rust would be found at the top of the cylinder barrel. This, when wiped off, meant that a certain amount of iron was gone. Under service conditions that loss of iron would occur at least once every day. Mr. ARTHUR HOARE, M.I.Mech.E., observed that the author did not define bore wear. One would surmise that in America bore wear was uniform, and dimensions which needed no explanation or qualification. That, however, hardly applied in Great Britain. Nothing had been said about the average journey lengths in the U.S.A. as compared with this country. The number of starts and stops made per thousand miles was closely associated with the question of corrosion; and he felt that corrosion could not be dismissed lightly. The author turned from the question of suitable materials and, almost sneering at austenitic sleeves and rings as a solution, mentioned five points—of which only the first had any quantitative definiteness—which ensured long life of cylinder bores regardless of the materials used. It was here that the greatest exception must be taken to the information which the paper contained. Whilst it might be contended that the examples he wished to bring forward were not applicable because of their size or piston speed or side thrust or connecting rod stroke ratio, the fact remained that with 28 liners in continuous use under similar conditions, and all showing similar indications of wear, the various data obtained with change of material or function could be readily repeated and accepted as a definite achievement by a definite method. An investigation into cylinder liner wear gave the following information. The average increase in diameter per cylinder at the worst position—fairly close to the arrest point of the top piston ring at the top of the stroke—was 0·005 inch per 1,000 hours working. The liner was of a standard type and this wear persisted fairly regularly through every liner in every engine under review. Using a special mixture iron with an inexpensive alloy, with no change in lubrication or other operating details, the wear was less [I.Mech.E., 1939] Fig. 6a Fig. 6b Fig. 6c Fig. 6. Thermostatically Controlled Heated Intake Manifolds Fig. 7. Tubular Ejector and Air Collector Fig. 9. Effect of Blow-by on the Surface of the Ring Fig. 15. Arrangement of Apparatus for Measuring Oil Consumption Text in images: WEIGHT FLAP HEAT AFFECTED SPRING | ||