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).
Piston design, specifically the location of the piston pin and the use of shorter connecting rods to address piston knocks.
| Identifier | ExFiles\Box 181\M11\ img166 | |
| Date | 1st April 1919 | |
| To R.Y. from R.{Sir Henry Royce} Copy to Ed.{J. L. Edwards} " " EH. ORIGINAL. RE PISTONS. I have received Mr. Hives' note with reference to the piston knocks. It will be understood that with reference to this subject that we have always tried to locate our piston pins low down the pistons where the piston fits the cylinder better than at the top end which has to have ample clearance for temperature variation. We have watched other people and find that although several fit much longer pistons than we have, none of them took advantage of these long pistons by placing the pin at the bottom end of the piston. The only way, however, this can be done without entailing a high and heavy engine is by the use of the relatively shorter connecting rod. Mr. Elliott had pointed out that in making the aero engines as light as possible, we adopted a shorter proportion of rod than was usual in the car, and that other makes of engines had still shorter rods than those on our aero engines, so that we might try a short rod in the chassis to get advantage of putting the piston pin low down. Mr. Hives has now demonstrated that this has the effect anticipated, and I think that the cylinders will not wear any worse, because of the short rod, owing to the fact that the angular thrust of the connecting rod falls on a part of the piston which is better lubricated, so that it is now imperative for us to push on with the short rods as tested. It will also be noticed that the scraper ring cannot now be below the piston pin, and it may be necessary to prevent (Contd.) | ||