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).
The testing of Cadillac-type automatic tappets for Vulture and Phantom cylinder heads.
| Identifier | ExFiles\Box 17\6\ Scan193 | |
| Date | 20th February 1934 | |
| X 7060 20.2.34. Report on Cadillac Type Automatic Tappets for Vulture & Phantom Cylinder Heads. As a result of the results obtained on J-III silent tappets, two sets of such tappets have been constructed - one for the Vulture Cyl. Head and one for a Phantom Cyl. Head. These have been tested and the results and conclusions drawn are dealt with separately, as follows :- VULTURE. This set of tappets, as received from the Fitting Shop and fitted to the engine, did not work satisfactorily at first, owing to lack of end play on eccentrics and also tightness of eccentrics on shaft. After having these matters remedied, they functioned fairly reliably at engine revolutions up to approximately 3000 r.p.m. Above this speed, however, a fresh trouble presented itself - as soon as the r.p.m. exceeded 3150 the power of the engine fell off and it exhibited signs of having its valves held off their seats. On shutting down this was confirmed and they continued to be held off their seats at idling speeds for a long period - ten minutes or more. It was deduced that this trouble was due to valve bounce or incipient valve bounce, possibly started by valve spring surge, and to confirm this, the valve springs were changed for (a) a set which gave a higher loading with same rate, (b) a set which gave a lower loading with same rate. The results of these changes were (a) to put the speed at which trouble occurred up to 3350-3400 r.p.m., (b) to bring the speed at which this trouble occurred down to 2500 r.p.m. These results confirmed the valve bounce theory, but although the valves were examined at the above speeds with a Rotescope, no visual signs of valve bounce could be detected. Hence it is assumed that only very slight bounce is necessary to produce this trouble. | ||