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).
Development of a photographic valve motion indicator to study the difference between actual and theoretical valve lift at speed.
| Identifier | ExFiles\Box 17\6\ Scan324 | |
| Date | 29th November 1934 | |
| To E.{Mr Elliott - Chief Engineer} c. to Wor.{Arthur Wormald - General Works Manager} Hs{Lord Ernest Hives - Chair}/Smth.12/KW.29.11.34. Development of a Photographic Valve Motion Indicator. As a result of development work on automatic tappet adjusters the conclusion has been arrived at that positive contact may momentarily break down at some point in the valve mechanism at speeds very much lower than the bouncing speed as commonly understood (i.e. the speed at which the valves bounce on their seats sufficiently violently to cause a drop in power). This fact has necessitated an increase in valve spring loads when silent tappets are fitted. On Ph.II this increase amounts to 13½% in spite of the fact that the valves have been lightened. Both the adoption of silent tappets and the general tendency towards higher engine speeds emphasise the need for an investigation into the actual motion of the valves when an engine is running. Owing to several factors there is a considerable discrepancy between the actual and theoretical valve lifts and a certain amount of experimental work will be necessary if we are to get the highest possible bouncing speed without increasing the spring loading or decreasing the valve lift. With this end in view an experimental rig has been developed to enable a photographic record to be made of the valve motion under running conditions. This rig is built on similar principles to the one used by General Motors. Fig. 1 shows the arrangement of the apparatus. A portion of a scrap Ph.II crankcase top half, cylinder block and head were used, the camshaft being turned by a variable speed D.C. motor. A canopy was built over the apparatus so as to exclude light during the photographic tests. During an experimental run the procedure was to expose the sensitized paper with the camshaft running very slowly so as to obtain a standard reference diagram. The camshaft was then run at the speed intended for investigation, and a second exposure made over the first. On developing the paper, comparison of the two diagrams showed the departure of the actual valve lift at high speed from the theoretical. | ||