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).
Comparison of the manufacturing and design differences between 'Delco' and 'HS/Rm' type split damper pistons.
| Identifier | ExFiles\Box 28\1\ Scan277 | |
| Date | 31th August 1931 | |
| SPLIT DAMPER PISTONS. COMPARISON BETWEEN "DELCOS" & HS{Lord Ernest Hives - Chair}/RM{William Robotham - Chief Engineer}'S TYPES. The "Delco" piston is turned to the finished dia. and the end face is squared up at the same setting. These settings form the location for the subsequent operations, milling, drilling and counterboring. There is a clearance of approx. .025" between the longitudinal faces when the two halves are fitted together. The guide pin holes are apparently drilled with a standard .250" drill, leaving the pins (which are .001" to .002" under .250") a shade slack. Thus when the piston is in position in the cylinder, the only direct contacts are between the inter-lever and the wearing pads, and between the turned diameter and the cylinder bore. Therefore each half of the piston is independent to a certain extent of the remaining section. It was anticipated that this slackness would cause noise due to the two portions of the piston rolling and to avoid this the limits were decreased all round when producing the HS{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer} type. When the end face is turned (on the HS{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer} type) a small "centre" is left for grinding, and after coupling up the two halves, the complete piston is ground on the outside diameter, the two sections being held together by long bolts running the full length of the piston with a "fitting" portion on each side of the joints. Therefore the accuracy of the piston depends upon the two long bolt holes, and any discrepancy in the distance between the C L's of these holes and the centre of the contact pad holes will cause difficulty when finally erecting the piston in the cylinder, since the total clearance allowed between the sides of the inter-lever and the corresponding walls of the piston is only .002". (We understand that this clearance is now being increased to .005". The "Delco" pads are secured in the piston by self-impressed serrations, whereas in the HS{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}, the piston has plain reamed holes, the stems of the holes being ground to fit. To retain the contact pads in contact with the inter-lever, "Delco" use only one spring, whereas the Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer} contains two. Also in the "Delco" the two long bolts are replaced by one short screw and a short piece of steel pressed into the "unspring" half of the piston to act as a guide pin. | ||