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 letter from Specialloid Limited discussing piston design, heat conduction, and clearances.
| Identifier | ExFiles\Box 148\4\ scan0287 | |
| Date | 22th September 1934 | |
| SPECIALloid LIMITED Friern Park North Finchley. N.12. -2- Messrs. Rolls Royce, Ltd., 22nd September, 1934. purposes its original shape under working loads and that undue stresses will not be set up at any one part of the Piston to cause excessive wear or section fracture. To this end we have persevered with the solid trunk Piston and by addition of eight thin webs radiating from the centre of the crown to the ring belt wall and an I-section strut above each gudgeon pin boss directly connected to both wall and crown, we have produced a rigid construction which does not increase the total Piston weight above the average. The crown and wall sections are proportioned in conjunction with the gudgeon pin bosses and web construction according to the working conditions of the engine (combustion pressures, head and block design, maximum revolutions, etc.) 2) Conduction of heat depends primarily on the material properties but the arrangement of the metal can of course assist or obstruct rapid heat conduction. The construction of the Specialloid Piston by virtue of the webbing system and boss struts, definitely assists in the rapid transference of the excess combustion heat from the crown to the Piston rings and cylinder wall via the upper ring belt. 3) External design. Compression and scraper ring layout and land clearance vary for individual engines and all are the main factors controlling the performance with regard to running power, oil consumption and actual Piston life. In this letter we cannot deal in detail with the many compression and scraper ring arrangements which combined with special oil return features are necessary for different type Pistons but we feel it will be sufficient to refer to our years of practical experience in this connection with Pistons, particularly with regard to the commercial types which often have to operate under extremely arduous conditions. The land clearances, however, are not such a variable factor or perhaps we should say are more closely related to the internal design and material of the Piston. The minimum running clearance which is the real concern of the automobile engineer can only be obtained by the scientific blending of the three essential factors - 1) Internal construction, 2) Material and 3) Actual clearances. 4) Actual clearance. A Piston cast from an alloy with a low co-efficient of expansion will not give the minimum running clear- | ||