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).
The policy of adopting aluminium pistons and a list of various piston designs to be tested.
| Identifier | ExFiles\Box 181\M11\ img123 | |
| Date | 18th December 1918 | |
| (2) PISTONS. X 2484 Our policy with regard to the treatment of the piston question should be somewhat altered. We must endeavour to give pistons more clearance and more oil. There is no doubt but that we must adopt aluminium pistons immediately for the 40-50 H.P. chassis, an important reason being thatthey never gall the cylinder and therefore never cause a breakdown by seized pistons. Mr. Hives points out that apart from the known advantages, the number of miles that the engine will run before carboning up and causing detonations, is very greatly increased. X.3400 The Works are about to test a new proposed die cast design of chassis piston, to LEC.1016, in which a large fully lubricated surface is provided for the piston control, and the scraping effect is immediately below the four piston rings. To obtain the most desirable proportions for this piston, the connecting rods have been shortened to a ratio of connecting rod length to crank used on the aero engines. The piston rings on this piston are some little way from the crown, in accordance with the practice found best for preventing the carboning up of the top rings. Mr. Royce points out that the fact of clearing away the metal above the top ring until the piston diameter at that point is .025" less than the cylinder bore creates a strong tendency to scrape oil upwards into the combustion chamber, and he now proposes a further model of piston in which the distance between the crown and the top ring, shall be still larger, and there shall be a fitting band immediately above the top ring, so as to cancel the scraping effect upwards. The pistons we wish to test for comparison in the chassis engine can be enumerated as follows:- (a) X.2369. Zephyr type aluminium piston to drawing LeC.602, similar to the design at present standard on the "Eagle", but perhaps with five instead of seven piston rings. (b) X.1799. Old type of barrel piston in aluminium with diagonal webs, on test in chassis engine sometime before the War. (c) X.3400A. Die cast aluminium piston to LeC.1016, with short connecting rod. (d) X.3400C. Improved die cast aluminium piston with fitting band above top ring to prevent upward scraping effect. This piston to be tested with short rod. Contd. | ||