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).
The design and testing of engine tappets, discussing noise, clearances, and performance.
| Identifier | ExFiles\Box 17\6\ Scan204 | |
| Date | 25th April 1934 | |
| -3- HS{Lord Ernest Hives - Chair}/Swdl.{Len H. Swindell}2/KW. 25.4.34. An Enota petrol filter has been placed in the oil feed line as the smallest particle of dirt is fatal to the operation of these tappets. When the oil is reasonably cool, below say 40°, the tappets are dead quiet, but with oil temperatures ranging from 70° to 100°C., they are audible if listened for. This noise is identical with that of standard tappet clearance set at .003 with a hot engine and it may be assumed that .003 is the amount which is lost by the oil squeezing out during each cam lift. This implies that the leakage factor is too high for the load to which the plunger is subjected and we think that the dimensions of this plunger mechanism are more suitable for the Bentley or 25 HP. unit for which we have produced an arrangement to Hs.{Lord Ernest Hives - Chair}1364. The diametrical clearance between the piston and plunger is kept as small as possible and limited from .00025 to .00075 that will not cause sticking when hot. A set of plungers are being produced in V.C.M. nitro-hardened to lessen any chance of sticking with these small clearances. The effect of the increased mass on the rocker arm reduces the speed at which valve bounce occurs from 3450 to 3250 r.p.m. with standard Ph.II valve springs, as judged by the falling off in power at this speed with Hs.{Lord Ernest Hives - Chair}1210 rockers, compared with standard rockers. As the valve gear generally is being investigated, the question of suitable springs for these particular tappets on the Phantom is not important. Attached is a print, EX.12871, which other than showing the arrangements Es.1206 and Es.1210 includes the scheme Hs.{Lord Ernest Hives - Chair}1209, the mechanism of which is a copy of the original Halford tappet as designed for the aero engine. This scheme did not function reliably at low oil pressures and trouble ensued with air trapping in the oil compression space, so that this arrangement was not persevered with to any extent. | ||