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).
Valve timing and design characteristics for the Aspin valve engine.
| Identifier | ExFiles\Box 134\1\ scan0225 | |
| Date | 21th June 1940 | |
| Jnr.{Charles L. Jenner} from Rm.{William Robotham - Chief Engineer} Rm.{William Robotham - Chief Engineer}14/ML.21.6.40. ASPIN VALVE. With reference to Jnr.{Charles L. Jenner}5/JH.18.6.40. the overlap which you show on the Aspin engine will not give poor low speed torque, but is likely to upset the idling. Since the Aspin valve, in any case, has an excess of area on the exhaust side, there seems to be no justification whatever for using such a long duration exhaust, particularly in view of the fact that towards the end of the closing the Aspin shows up a marked gain in area over the poppet valve. We think therefore that the right treatment for the Aspin valve for our engines, would be an inlet valve opening, 6 degrees before top dead centre and an exhaust valve closing 6 degrees after. We cannot see any justification for opening the exhaust more than 48 degrees before bottom dead centre. If we cut down the exhaust valve duration like this we can get quite a reasonable degree of overlap and yet use a long duration inlet. We should still like to see the proportions of Aspin Drawing No: C.144, applied to your PL.252, to see where we finish up. The other question I would like to ask you is, have we taken full advantage of the engine length? In other words, have we got the valve as big as we possibly can? It is really clear that only a test of the Aspin valve can indicate how it will compare with 4-valve aviation engine practice, but I am quite satisfied that it's breathing would be adequate for the 2-cycle engine we are contemplating. Could you contact Wd.{Mr Wood/Mr Whitehead} and see what Kadenacy is suggesting for a rate of opening, because the Aspin valve seems to have one big advantage in that it's rate of opening for the first 12 degrees is higher than that of any other valve gear which we at present use. Rm.{William Robotham - Chief Engineer} | ||