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).
Engine valve seat warping, comparing different models and proposing solutions.
| Identifier | ExFiles\Box 158\4\ scan0235 | |
| Date | 26th May 1938 | |
| -2- Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}4/R.26.5.38. (2) That the 25/30 is comparatively free from seat warping, and the metal section between the valves is .437. A 25/30 head, as 'mocked up' on a Wraith unit and run in 27.G.VI for 6,000 miles is free of the trouble. (3) That the 3½-litre Bentley is never as bad as the 4¼-litre Bentley, the former having a metal section of .350 against .250 on the latter. The conclusion from the above is that the thicker the section between valves, the less the distortion of valve seats, and tests being carried out are as follows both for confirmation and a solution to this trouble:- (1) Trial of venturi shaped inlet port which we know gives identical power to a standard shaped port, and although having the same section of metal in the proximity of the valve seats has a much thicker web section. This is shown on the attached drawing Rm.{William Robotham - Chief Engineer}531 and is being run on 28.G.VI to get in some mileage before inspection for warping. (2) We have run a head with a 1.5 diameter inlet and 1.3 diameter exhaust valve in comparison with the standard sizes 1.6 and 1.4 diameter respectively. This condition gives a metal section of .350 against the normal .250, and so far as we have run on the test bed, namely, 10 hours of power curves, etc. the seats are free from warping. This head, however, is, approximately, 4-6 B.H.P. down compared with standard valves, and we are going to open up the inlet back to standard to note if power is re-gained still maintaining the small exhaust valve, which will leave a metal section of .300. (3) The valves can be spread by, approximately, .125 which would approach the 25/30 metal sectional thickness, but is regarded as a last resource as it affects a number of things in the design and tear up of existing parts. Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} | ||