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).
Analysis of cam loading and valve gear performance for various engine designs.
| Identifier | ExFiles\Box 110\1\ scan0074 | |
| Date | 26th May 1941 | |
| Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}6/ET.26.5.41. 2. A.{Mr Adams} If the acceleration figures illustrated are to be thought of in terms of maximum loading of the cam, they do not mean very much without an accurate analysis of the valve gear weights. It is alleged by Mitchell on his preliminary B.60 valve lift drawing PD.83 that the maximum permissible loading is 1100 lb/in. width of the cam. It is claimed that the B.II loading is 1013 lb/inch @ 4200 R.P.M. With the cam in its original form the B.60 inlet cam loading was in the region of 650 lb/inch @ 4200 R.P.M. This cam, however, was chamfered at the nose in order to rotate the tappets. This resulted in making the line of contact shorter at the heavy acceleration changeover. It became about 35% of its original length and the loading went up to over 1800 lb/inch. Under these conditions the tappets showed signs of rubbing but did not fail. Since, in theory, line contact is made and the actual loading is infinite the cam or tappet must distort, and the actual loading is probably dependent on the static curvature of the cam. For what it is worth the Myth inlet cam loading is in the region of 1030 lb/inch @ 4750 R.P.M. B. As already explained in Ev{Ivan Evernden - coachwork}/JD.{J. Draper - Frames}1/SW.22.4.41, the velocity with which the inlet cam strikes the tappet on Myth has been increased to the same value as for the exhaust, which is the same as B.60 exhaust. (B.60 inlet velocity is reduced through the rocker ratio). The argument is that if this velocity is acceptable on the exhaust, it should be so on the inlet. With regard to noise on closing, the inlet and exhaust valves on the car engines all strike their valve seats at the same velocity, i.e. .0006 in/deg. or .075 ft/sec. @ 250 R.P.M. Rm.{William Robotham - Chief Engineer} | ||