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 theoretical effects of Cadillac automatic tappets on valve bounce speed and spring load for the Ph.II unit.
| Identifier | ExFiles\Box 17\6\ Scan256 | |
| Date | 21th June 1934 | |
| To E.{Mr Elliott - Chief Engineer} x7060 Hs{Lord Ernest Hives - Chair}/Smth.23/KW.21.6.34. Cadillac Automatic Tappets on Ph.II. The report Hs{Lord Ernest Hives - Chair}/Swdl.{Len H. Swindell}1/KW.15.6.34, deals with attempts which have been made on the Ph.II unit BJ-55 to overcome the tendency for the valves to be held off their seats when the Cadillac type of automatic tappets are fitted. The following additional points are of interest:- Theoretical Effect of Mechanism on Valve Bounce Speed. The diagram shows the arrangement of the mechanism. The spring under the plunger is loaded to 5 lbs. and the leverage of the eccentric is 8/1, giving a loading of 40 lbs. on the valve rocker spindle due to the plunger spring. If, when the engine is running, the sum of the loads on the two ends of the rocker falls below 40 lbs., the valve will be lifted off its seat. [Diagram with label: Sib SPRING] Examination shows, however, that even at 4,300 r.p.m. the theoretical valve bouncing speed for a standard engine, the reaction on the rocker spindle due to the accelerative forces would be 64 lbs. Hence, if the valves are operating according to the lift diagram, the Cadillac mechanism should not reduce the speed at which the valves bounce. This fact has been checked for every spring combination used in the trials. Effect of Spring Load. With the Vulture type head and the E.62448 camshaft, No. 6 exhaust valve was invariably first to give trouble. Table I shows the results obtained for this valve with different valve springs. | ||