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).
Power experiments investigating the effect of reduced piston friction by testing modified pistons.
| Identifier | ExFiles\Box 86\2\ scan0199 | |
| Date | 14th May 1934 | |
| Hs{Lord Ernest Hives - Chair}/Mths.{Reg Matthews}1/KW.14.5.34. Effect of Reduced Piston Friction (Bentley). Further to our report on Heat Balance Experiments (Hs{Lord Ernest Hives - Chair}/Mths.{Reg Matthews}1/KW.13.2.34), we have now completed Power experiments with the following Pistons. (1) EX.13398 Pistons which are the modified E.57122 Pistons referred to in the above report. These pistons it will be remembered have no sawcut down the skirt, the skirt has also been shortened .500 and the clearance in the cylinder bore is .020. (2) E.B.1404 Pistons (semi-split type). With regard to (1) we find that these Pistons give equal power to the Aerolite Pistons, there is a small reduction in power at the low speeds due to the excessive "blow past" of the gases when running with so much clearance. At the high speed end of the curve we have increased the power output by removing the bottom gas ring so that there were two gas and one scraper ring as on the aerolite. The aerolite piston rings however have a much wider bearing surface than the standard rings fitted to these pistons. This applies to both gas and scraper rings. The increase in power by removing the bottom ring was 2.2 H.P. at 4500 r.p.m. there was no increase at 4000 r.p.m. From the fact that we get such a small increase in power over the aerolite by the use of excessive clearance rather points to the excellent design of the aerolite piston from a friction point of view and, as mentioned in our previous report they are quite good as regards knocks. With regard to (2) the semi-split pistons, these are quite good at the low speeds almost reaching the performance of the aerolite pistons. The power falls off at high speeds, however, the power being 118 H.P. at 4250 r.p.m. as compared with 124.5 with Aerolite, the power at this speed with standard pistons being 116.8 H.P. | ||