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).
Running experience and performance issues of single bolt pedestal pistons, specifically concerning piston knock and gas leakage.
| Identifier | ExFiles\Box 15\3\ Scan023 | |
| Date | 12th October 1928 | |
| To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/ACL. c. to BJ. WoR.{Arthur Wormald - General Works Manager} c. to E.{Mr Elliott - Chief Engineer} DA.{Bernard Day - Chassis Design} c. to BY.{R.W. Bailey - Chief Engineer} +7040. Hs{Lord Ernest Hives - Chair}/ACL1/LG12.10.28. SS.{S. Smith} SINGLE BOLT PEDESTAL PISTONS. Lec.2554. +7040 E.77518. We have had considerable running experience on the test bed with the above pistons during development work and from time to time have kept careful record of their performance. The chief points which came to our notice were piston knocks when cold and gas leakage past the rings. It was very noticeable after full power running and when the engine had been allowed to cool down over-night, that piston knocks became very evident when starting up the next morning. The knocks became practically absent when the engine and oil attained normal working temperature. Examination of the pistons revealed score marks on the contact faces of the skirt which were 'eased' off and the piston carefully re-fitted. When re-tested the pistons were still prone to cold knocks although quite good at normal working temperatures. It is our opinion, based on this and previous experience, that this particular trouble is due to the bottom scraper ring which although an excellent feature for combating over-oiling troubles, becomes somewhat of a danger when used on our chassis engines. We have now, with our latest crankshaft and bearings, less oil discharge, a feature which would probably be most evident when the oil was cold. In the example mentioned when the engine is stopped down after hard running, the oil conti :- | ||