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).
Letter from a supplier discussing their design and manufacturing practices for valve springs.
| Identifier | ExFiles\Box 158\4\ scan0031 | |
| Date | 18th May 1936 | |
| COPY. X1360 Barnes-Gibson-Raymond-Inc., 6400 Miller Avenue, Detroit, Mich. 18th May, 1936. Mr. W.A. Robotham, Rolls-Royce Co., Derby, England. Dear Sir, We have received a letter from Mr. Alexander Taub requesting that we write you regarding our practice in the design and manufacture of valve springs. It is rather difficult for me to answer the questions which are in your mind without some idea of the information that you desire. I shall therefore outline as near as I can our practice, and hope if I do not make myself clear, you will write and ask me questions concerning it. The first thing to be considered is the design of the valve spring. We are very fortunate here in that our customers co-operate with us in furnishing us motors with the cam and valve mechanism they desire operated ready for us to insert springs and test them. Our first attempt is usually to design a spring for the correct loads, figured from the weight of the parts in the acceleration of the cam, allowing a small percentage for friction. These springs are put in the motor and they are looked at with some stroboscopic means. In our case either a mecury or neon light is geared directly to the cam shaft and synchronized with it. If the springs go into a surge period we usually try to make them self-dampening, and to do this we have coils which close before the valve closed position is reached, and after this position is reached and the valve starts to open, the spring further changes its own period as the coils continue to close, so that perhaps with a valve closed position we would have four active coils, and in the valve open position we would have but three and one quarter active coils. We have found that this takes quite a little work, as a difference of .010" in the spacing of these coils often means success or failure. The springs are of course designed to work within a definite stree range, and we have enclosed a copy of our work on helical springs in the catalog which is going forward to you under separate cover, also an additional copy of the stress range which we use in designing the valve springs. All the stresses are calculated by the Wahl formula which you will find in our catalog. | ||