Extract detailing the testing and performance of self-adjusting tappets for the Hs.1210 engine.
| Identifier | ExFiles\Box 158\5\ scan0081 | |
| Date | 25th April 1934 | |
| EXTRACT. Hs {Lord Ernest Hives - Chair} /Rm. {William Robotham - Chief Engineer} 1/KW.25.4.34. A complete set of self adjusting tappets to Hs. {Lord Ernest Hives - Chair} 1210 has been tested both on the test bed and in a chassis, with promising results. There is no sign of air locking under any conditions of running and if when stopped the oil is not allowed to drain out of the rocker shafts and oil pipes, the tappets function within 2-3 seconds of starting. If the draining is not prevented, it takes 20-30 seconds to operate when cold and 3-5 seconds when hot. Tests are at present being carried out to overcome draining. The standard oil feed arrangement to the rockers is used with a slightly stronger relief valve spring in order to maintain a pressure of not less than 5 lbs/sq.in. with the temperature at 100º C. and slow running. It has been necessary to by-pass the main valve by .062 dia. hole in order to obtain this condition. An Enots 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 40º, the tappets are dead quiet, but with oil temperature ranging from 70 to 100ºC., they are audible if listened for. This noise is identical with that of standard tappet clearances 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 H.P. 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 Hs. {Lord Ernest Hives - Chair} 1206 and Hs. {Lord Ernest Hives - Chair} 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. | ||
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).