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).
Letter from The S.U. Company discussing engine tick-over, noise, and mixture strength.
| Identifier | ExFiles\Box 31\4\ Scan069 | |
| Date | 24th August 1931 guessed | |
| THE S.U. COMPANY. W.A. Robotham, Esq., Messrs. Rolls Royce, Ltd. CONTINUATION NO. -2- Should you however, wish for an even better tick-over on this engine, I think it would be worth trying something along the lines of the sketch we discussed, in which piston leakage is cut out during idling by concentrating the air flow round the main jet by means of a passage drilled in the piston which can be brought to coincide with a port in the choke wall running directly to the neighbourhood of the butterfly. With regard to the matter of noise, it is obvious that this at the moment is rather serious. Mr. Skinner has instructed me to sketch out a pipe somewhat similar to that used on the Morris Oxford Engine for hot air, which could be carried back alongside the engine to draw its supply through a large air cleaner of the Vokes type, and I will forward you a sketch showing a suggestion on Thursday next (the 27th instant). I think a really efficient silencer of this type will serve to eliminate even the pronounced hiss which we appear to get at about 2/3rds of the piston lift. The third matter to which we have to give our consideration is that of providing mixture strength variation without affecting the idling adjustment. This, of course, presents considerable difficulty, except in the case where a separate slow running jet is employed. In fact the only solution which occurs to me at the moment, is to provide some mechanical restriction such, for instance, as a spring load to operate upon the choke piston. While in action this, of course, would increase the mixture strength by virtue of an increased depression and therefore air speed across the jet, without however effecting the setting for idling. Although we have not conducted any investigation along these lines it does present a possible solution, and we shall be interested to hear your views on this point. The fact is that with a perfectly cold engine the strength for the tick-over position does require to be rather greater than under normal working temperature conditions. continued:- | ||