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).
Investigating the failure of pistons on Geoffrey Smith's car, proposing material changes and further testing.
| Identifier | ExFiles\Box 90\2\ scan0075 | |
| Date | 26th May 1937 | |
| Rm.{William Robotham - Chief Engineer} c.C. c.Hs.{Lord Ernest Hives - Chair} 261 BY.1/G.26.5.37. MATTHEWS. RE: FAILURE OF PISTON ON GEOFFREY SMITH'S CAR B.100-GA. -------------------------------------------------- The results of the investigations which have been carried out by Messrs. Light Production Ltd. and in our own Laboratory show no reason for the failure of the pistons. The structure of the material appears to be satisfactory, and the only point which can be raised is that the magnesium is on the low side of the limit, but the variation in strength due to this can only be a small percentage, and furthermore we must have reasonable limit on the materials. In this connection, however, we propose to slightly raise the mean magnesium figure. The failure was not an isolated one in Geoffrey Smith's engine, as you will remember that whilst one piston had completely parted at the circumferential slot for trapping heat a second one had commenced to fail. From an examination of the parts it was clear that the engine had not been driven at abnormally high speeds, and the fact that cars which have been driven at abnormal speeds, such as Raymond Mays, have done 35,000 miles without failure against less than 10,000 miles on Geoffrey Smith's, might suggest that the higher temperature of the pistons under the heavy work imposed by Raymond Mays may have resulted in a better condition for resisting cracking at the oil return hole in the scraper ring groove where the trouble started by reducing its brinell and making it somewhat softer. We would therefore like to have a piston from a car which has done a long mileage to compare with the results we found on Geoffrey Smith's car. Rm{William Robotham - Chief Engineer}/Mts. promised to obtain this piston, but so far I have not received it, and it is important that we should leave no channel unexplored which may throw light upon the cause of the failure. There are two suggestions we would like to make which might be helpful in locating the trouble :- (a). We would suggest two sets of pistons are taken from production, one set is run at relatively low power with only very occasional short bursts of high speed and the second set is run at the high speeds and powers in the usual way. If there is anything in the suggestion I have made above then this experiment might confirm the views or wash out the suggestion completely. | ||