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).
Automatic tappet trouble on the Vulture engine, theorizing valve bounce as the cause and requesting information on Cadillac's experience.
| Identifier | ExFiles\Box 173\1\ img112 | |
| Date | 26th January 1934 | |
| To Rm.{William Robotham - Chief Engineer} from Hs{Lord Ernest Hives - Chair}/Std. The Athletic Club, Detroit, Michigan, U.S.A. Hs{Lord Ernest Hives - Chair}/Std.18/KW.26.1.34 Cadillac Type Silent Tappets. We are having trouble with the automatic tappets for the Vulture engine when running at top speeds. The trouble, which commences at a definite speed for a given set of valve springs (3150 r.p.m. for the double taper springs instructed for this head) consists of a drop in power after a very short period of running (say one minute) pointing to the fact that the valves, both inlet and exhaust, are being held open. This is confirmed if we shut down and check the valves. Using valve springs of different loadings (but same rates) we can produce this trouble at 2500 r.p.m., 3150 r.p.m. and 3400 r.p.m. Our theory is that the trouble is due to valve bounce - this may be only very slight - which is followed up by the eccentrics and plungers; the latter being unable to leak sufficiently quickly to allow the valve to seat when cam and valve gear are in contact again. We should like to know whether the Cadillac people have had any trouble due to valve bounce, as we cannot see how an automatic tappet mechanism can fail to break down when this occurs. Weaker plunger springs and larger plunger clearances have been tried without improvement, but we are proposing to try higher rating valve springs. Hs{Lord Ernest Hives - Chair}/C.S. Steadman. | ||