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).
Modifications to improve engine idling on the high power head.
| Identifier | ExFiles\Box 132\4\ scan0253 | |
| Date | 27th October 1940 | |
| Jnr.{Charles L. Jenner} from Rm.{William Robotham - Chief Engineer} c. EV.{Ivan Evernden - coachwork} Cylinders general 1124 re IDLING OF THE HIGH POWER HEAD. We are not very happy about the potential idling of the Myth engines. The engines we have already made are none too good, and bad slow running on a "4" is likely to be more obtrusive than either a "6" or an "8". The trouble is due to the very large inlet valve which we have, having a high leakage factor when it is on the toe of the camshaft. We can get good idling with 15 thou: tappet clearance, but bad at 10 thou: We have therefore got to try and reduce the leakage factor between 10 and 15 thou: A very wide inlet valve seat should obviously improve matters. We should like you to look into the matter and see by what percentage you think you could increase the seat width. In addition to this, slight pocketing the valve to the extent of .015, with an annular clearance of .005, should help matters. The lost lift on the valve could be restored by a small alteration in the rocker ratio. If the above modifications improve the idling considerably, then we should be quite optimistic with regard to a fully masked valve, if we did it in the right way. We have, of course, tried it once before but we were not very thorough about it. If the modifications we suggest do improve the idling, we will get out some quantities as a basis for a masked valve, with a special camshaft to suit. Rm.{William Robotham - Chief Engineer} | ||