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).
Design and performance of Myth valve diagrams, springs, and cam forms.
| Identifier | ExFiles\Box 110\3\ scan0127 | |
| Date | 26th April 1941 | |
| 754 1030 To Rm.{William Robotham - Chief Engineer} from Ev{Ivan Evernden - coachwork}/JD.{J. Draper - Frames} Copy Ev.{Ivan Evernden - coachwork} Rm{William Robotham - Chief Engineer}/HH. Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation} MYTH VALVE DIAGRAMS. We attach to Rm{William Robotham - Chief Engineer}/HH's copy the original of the valve acceleration, velocity and displacement diagrams for Myth, PL.533. Myth valve springs (RE.1887, RE.1888) were already in being when this design was begun. The decelations have been arranged such that these springs will be satisfactory from a loading point of view at 4750 RPM. The excess of spring load over decelerating force is not constant over the decelerating portion of travel. This is to enable the nose section of the cam to remain circular and of the largest possible radius. In the case of B.60 a factor was used in the deceleration formula to make the excess spring load the same at all points of the deceleration. This has the effect of producing a cam nose of a varying radius, the radius decreasing as the centre line of the cam is approached. In other words, for the same lift and duration, the ideal excess spring load condition may be satisfied at the cost of a more pointed cam. The B.60 cams were designed for a spring rate which was subsequently altered, and these springs (EB.3256) were used on the exhaust valve without trouble although the excess load at one point was only 5 lb. at 4200 RPM. It has not, therefore been considered necessary to adhere strictly to this ideal. The advantages gained by not doing so are:- a - a simplified cam form, and b - a larger nose radius. This is of much importance if the camshaft is ever to be made in 'Monicrom'. Ev{Ivan Evernden - coachwork}/JD.{J. Draper - Frames} Original to Rm{William Robotham - Chief Engineer}/HH. Prints to Ev.{Ivan Evernden - coachwork} Rm{William Robotham - Chief Engineer}/HH. and Ashby. | ||