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 Wilcox-Rich discussing cam design, valve lift, tappet types, and camshaft materials.
| Identifier | ExFiles\Box 174\2\ img235 | |
| Date | 28th December 1937 | |
| WILCOX-RICH a DIVISION OF EATON MANUFACTURING COMPANY 9771 FRENCH ROAD DETROIT, MICHIGAN PLANTS MARSHALL BATTLE CREEK PRODUCTS VALVES VALVE SEAT RINGS TAPPETS HYDRAULIC LIFTERS December 28, 1937 Mr. A.{Mr Adams} A.{Mr Adams} Robotham Rolls-Royce, Ltd. Derby, England Dear Mr. Robotham: Regarding your inquiry of the 6th with reference to lifts over .550, the only thought I have on this is to design the cam following the method outlined in the attached paper. This permits maximum possible lift for a given set of conditions; i.e.: fixed tappet diameter, bearing diameter, etc. I have cut this down more or less to the data shown on the attached sheet although I have not taken into account the desired ramp but this is quite clear in the paper and I am sure you will have no difficulty with that. It is not necessary to show flank radii, etc. on the cam drawing if a chart of degrees travel against lift is covered and we suggest that you follow this procedure; then the master cam manufacturer can work directly from this chart. would suggest a limit on the rate of rise to very not more than .0002" per degree. I do not quite understand your reference to the Hudson but I infer that you mean they are using their present design to enable them to get the highest possible lift. They are using a lift of .343" with quite a wide timing angle which with a follower of reasonably large radius enables them to obtain a relatively full cam. However, if the same angle is maintained and the cam designed according to the attached paper, then a somewhat better outline is the result with the advantages of the mushroom type from the viewpoint of lower maximum spring pressures although the acceleration is high. The maximum lifts that we have encountered are on commercial engines where the speeds are relatively low; one being .570 and the other .400. As far as materials are concerned, we have obtained the best results with a chilled-type of tappet and a case-hardened camshaft. Of course, the chilled-iron shaft with a steel lifter is also giving good results but we do not have knowledge of anything of this type operating with as heavy loads as are carried on the first combination. Whether the tappet is the all-steel type with the puddled face, or the built-up type, does not seem to be much of a factor. We would be very much interested in learning whether or not you still consider the Brightray when used on valve seats as well. [Handwritten Note] A.C.L. Could you give me this information for Young. Sim | ||