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).
Oil feed to rockers, valve operation, and associated noise issues, including tappet clearance and camshaft design.
| Identifier | ExFiles\Box 96\2\ scan0232 | |
| Date | 1st June 1937 | |
| -2- (3) The oil feed to the valve tip through the rockers was also in excess of what was desired in view of our past troubles. This was metered down to what we consider correct by drilling the hole in the rocker bush (.062 dia) and not the full sized hole of the same bore as that drilled in the rocker. Our experiments are leading us to the fact that it will be possible to replace the milled flats on the rocker shafts, together with the .031 dia holes by .062 holes drilled horizontally, and which are not in line directly with the rocker hole. We are fixing up the 15,000 mile unit in the above manner according to the drawings Rm.{William Robotham - Chief Engineer}380/1/2, and will confirm our initial results. (4) In order to obtain the following pressures which we consider satisfactory as run at 4,000 R.P.M. and 100° inlet oil temperature we have had to modify the relief valve springs in accordance with (Rm.{William Robotham - Chief Engineer}384/5). NOISE. As previously stated, in its present new condition the valve operation is very quiet, and we would say that with the rocker covers in position, is as quiet as the present hydraulic system. The camshaft, which is to LcO.5401, has low velocity opening and closing toes up to .020 of the valve lift. Our observation on noise has been with a tappet clearance of .012, at .015 the noise is just audible which shows that if set at .010 cold there is no "Warming up period noise". It is, however, more reliable to set at .012 with the engine thoroughly warmed; both oil and water. The figure of .012 is sufficient to allow the exhaust valve full expansion (.008-.010) at high speeds full throttle without being off the seat. Our chief concern on the noise question is whether, after long periods of running when the seat has distorted slightly, the valves will become noisy on seating due to the "cookover" on the seat, allowable by the clearance in the valve guide. | ||