Technical report on carburetter adjustments, exhaust valve issues, and preignition testing from France.
| Identifier | ExFiles\Box 11\4\ 04-page036 | |
| Date | 6th May 1932 | |
| To Hs {Lord Ernest Hives - Chair} /Rm. {William Robotham - Chief Engineer} From G.W.H. X7941 Hotel de France, Chateauroux(French test region), FRANCE. May 6th 1932. 19-EX. RE. CARBURRETTER. We have overcome the "kick back" or "luffing up" when accelerating from slow speeds, by fitting a spring under the air valve to lessen its weight for the first portion of its lift. It now lifts more readily and is not so sluggish for light opening of the throttle, and consequently overcomes the flat spot. The spring becomes inoperative after an approx. lift of .025" of the stroke of the piston, so does not interfere with the metering of the carburetter at higher speeds. We have changed the needle from 3°.28 to 3°.12 to try and cut down the petrol consumption at high speeds. We find that up to speeds of 75 m.p.h. we get an average consumption of 10.4 m.p.g. but over this speed it drops to 8 m.p.g. We have got more spare needles to further reduce it, if we find it necessary. RE. EXHAUST VALVES. We shall have to have some spare exhaust valves E.82459, as No.2 & 5 are stretching. They have already gone approx. .015". This happens during the time the engine is preigniting, as during our run to Le Canadel(Henry Royce's French residence) and back, the clearance was maintained, and it is only since higher speeds, with the preignition, that the trouble has occurred. I believe they have longer shanks than standard, and only six were made. Re. the push-rods bending. We are certain that these must have been bent when the engine was first started up, and the asbestos packings were full length, as there is ample clearance between the coils of the springs. RE. PREIGNITION. As events have turned out, we are fairly satisfied that during your run on Brooklands you were only using the magneto ignition, and consequently did not run into preignition trouble. We have definitely established the fact that a considerable distance has to be run on one ignition to bring about preignition, where as with the two ignitions three miles is sufficient to produce preignitions, so bad that the engine will continue to run, power falls off and speed drops. You are aware that we found the coil ignition out of action after crossing over, and we came to the conclusion that it had petered out during your tests. | ||
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).