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).
Series of questions regarding a report on oil consumption and cylinder wear, particularly concerning Bentley engines and piston ring design.
| Identifier | ExFiles\Box 144\3\ scan0267 | |
| Date | 11th October 1937 | |
| Oil Consumption File. 1220 To Rm{William Robotham - Chief Engineer}/Mths.{Reg Matthews} from Rm.{William Robotham - Chief Engineer} OIL CONSUMPTION AND CYLINDER WEAR REPORT. We have read your report on Oil Consumption with considerable interest. We should like to have an answer to the following questions:- (1) You state that you believe the increase in cylinder bore wear from the 1st. to the 2nd. series Bentley was due to higher compression rings being used. You point out that the 'L' section rings are more effective in controlling oil consumption and at the same time do not have the same tendency to flutter at the theoretical vibrating speed as the normal type of ring. This being so, why have we not persevered with the 'L' section ring on Bentley instead of higher unit pressures.? In any case, we should have thought that an 'L' section ring giving a pressure of about 18 lbs/sq.in. would have been better than the present standard type of scraper ring giving 32 lbs/sq.in. We should have thought this could have been easily obtained by using a Chevrolet section compression ring and removing an L. section ring from the back until the required unit pressure is obtained. (2) We should have thought we should have blow-by figures with L. section rings. (3) What evidence have we to show that with the present standard L. section ring used on the 25/30. we get bad oil consumption above 4000 R.P.M.? (4) Are we sure that the increase in oil consumption with oil pressure above 35 lbs/sq.in. is not due to the oil supply to the valve gear increasing on this pressure and causing oil to go down the valve guides.? (5) Have we no figures to show loss of power with high pressure rings and also increase in starting torque necessary.? We know that O.B.IV. does not start as readily as previous Bentleys. (6) What we should do at once is to take advantage of the Cold Chamber to get comparative results on cylinder bore wear. We ought to have a test stand made to which we can fit an engine. continued | ||