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).
Technical report on the performance and testing of self-adjusting tappets and related valve train components.
| Identifier | ExFiles\Box 158\5\ scan0086 | |
| Date | 25th April 1934 | |
| Hs{Lord Ernest Hives - Chair}/Swdl.{Len H. Swindell}2/KW.25.4.34. - 2 - (1) As the cam starts to lift, the inertia in Hs.{Lord Ernest Hives - Chair}1210 tends to throw the ball on to its seat, other than by the oil pressure in the compression space. Hs.{Lord Ernest Hives - Chair}1206 tends to throw the ball off its seat as the cam starts to lift. (2) At low speeds where cam accelerations can be neglected, the main load on the plunger is exerted by the valve spring. With the radius of the rocker lever being 1.7" on the valve spring and 1.3 on the push rod, the loading on the plunger at the valve spring Hs.{Lord Ernest Hives - Chair}1210 is only 76.5% of the plunger loading at the push rod Hs.{Lord Ernest Hives - Chair}1206 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 100° 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 Enot 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 the oil temperature ranging from 70° to 100° C., t 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 | ||