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).
Design considerations for connecting rods and pistons for the 3 1/2 litre Bentley engine.
| Identifier | ExFiles\Box 3\6\ 06-page122 | |
| Date | 26th January 1934 | |
| To Hs.{Lord Ernest Hives - Chair} from E.{Mr Elliott - Chief Engineer} X 4553 E.6/HP.26.1.34. c. Sg.{Arthur F. Sidgreaves - MD} Wdr. By.{R.W. Bailey - Chief Engineer} 3 1/2 litre Bentley.- Connecting Rods and Pistons. Replying to your memos Hs.{Lord Ernest Hives - Chair}4/WJ.24.1.34 and Hs.{Lord Ernest Hives - Chair}5/WJ.24.1.34, we are of the opinion that we ought to produce some further sets of the Leyland type of rod but made to LeC.3682. This rod is not so bulky in the stem as the experimental model, and has more clearance with the bottom edge of the cylinder bore on the extreme side positions, which latter feature we think is definitely required on production. The small end of LeC.3682 is suitable for either the large or the small gudgeon pin. The big end is fitted with a 10 thou. shim with a dowel for positioning same. We should like to have your opinion as to whether you think this is necessary. We should prefer to do without these features from a design point of view, but it has always been R.R. practice to provide facilities for the adjusting of big end clearance on car engines without filing the cap face. With regard to the question of the pistons, we agree that LeC.3699, which is a semi-split shorter and lighter piston than the present standard is the one in which we are interested. This piston has also been designed with a ribbed crown, and we have instructed the SpectreCodename for Phantom III pistons on the same lines. With regard to the diameter of the gudgeon pin, we should like to take this opportunity of introducing the larger diameter because we believe it will be beneficial to the piston in the long run, and the increased bearing area is also beneficial as regards the small end of the aluminium rod. No alteration would be required to the piston casting or the connecting rod forging for this larger pin and the increase in weight need not be more than .25 of an ounce. | ||