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 development, discussing camshaft clearances, valve bounce, springs, timing gears, and lubrication.
| Identifier | ExFiles\Box 6\6\ 06-page258 | |
| Date | 19th August 1937 | |
| -3- noted from the above that the practical clearances for quietness with each cam are the same amount short of the theoretical figures, which leads us to believe that this may be partially due to 'squash out.' This shortness figure of approximately .010 on Wraith III. can be compared with a figure of .005 on the 25/30 and is attributed to the higher rocker ratio on the former, with a consequently greater load on the mechanism. With our latest long toe camshaft Rs.{Sir Henry Royce's Secretary}607 as previously mentioned with theoretical quietness up to .020 clearances, the valve gear is satisfactory up to .008 - .010 at idling speeds, but there is a period at 1500-1600 R.P.M. which is objectionable, but hardly detectable from the driving seat. By use of the information on the mock-up unit, regarding the reduced valve lift with consequent weaker valve springs, we anticipate that it may be possible to make the Wraith valve mechanism a good job. VALVE BOUNCE AND SPRINGS. Since during the 'scuffing' and consequent damage to the camshaft we have again checked over the valve bounce figures and find that with the Rs.{Sir Henry Royce's Secretary}540 springs and Rm.{William Robotham - Chief Engineer}400 top washers, the valves are just starting to bounce at 4400 R.P.M. The above arrangement gives a closed valve spring length of 1.625 with a seat loading of 50 lbs. and has close coiling of the two base coils for anti-surge. These have been coiled in our own works in Swedish heat treated wire. Although the choc-stress is not in excess of 90,000 lbs/sq.in. we have had several failures, but are proceeding with our investigation of this particular wire as coiled by us, in view of its cheapness. TIMING GEARS. The gears on No.3. and No.4. units have been a considerable improvement on the first No.1. and 2 units and undoubtedly due to more correct production of the gears and set up. An experimental set of gears with a higher helix angle are being produced in accordance with instructions by Rm{William Robotham - Chief Engineer}/PJR. for trial. LUBRICATION Having a definitely controlled pressure to the valve gear, the flow to the valve tips is excessive and would undoubtedly run us continued | ||