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).
Faults with aluminium pistons, specifically loud knocking and carbon deposits.
| Identifier | ExFiles\Box 35\2\ scan 189 | |
| Date | 15th January 1920 | |
| X2748 To R.{Sir Henry Royce} from Hs.{Lord Ernest Hives - Chair} c. to CJ. c. to Bn.{W.O. Bentley / Mr Barrington} c. to E.{Mr Elliott - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} c. to EP.{G. Eric Platford - Chief Quality Engineer} Hsl/LG15.1.20. X.2748. - RE ALUMINIUM PISTONS. X.3715. X.682. X.2631. During the recent run to W.W. on 49-GB we noticed that this Car developed a similar fault to what you experienced on 7-CA i.e. when the car was going at full throttle high speed it developed a loud knocking. We have dismantled the engine and find that the pistons on this car have a similar appearance to those which were on 7-CA at the time when it had the same trouble. On 7-CA we attributed some of the cause of the trouble to the fact that the piston ran past the cylinder bore into the combustion chamber. With the present pistons on 49-GB, however this does not occur. The pistons we were running on 49-GB were the ram type - the rams had a single ring fitted to them. These pistons had only run on 49-GB a matter of 600 miles. We think the reason this car developed this trouble so quickly was because, as we know, it was over-oiling and forming a carbon deposit rapidly. The pistons were very badly carboned after the 600 miles running also the engine detonated badly when run at full power. We first came across this trouble on the aluminium pistons with the rings low down. To overcome it we turned a clearance band on the top band of the piston leaving a band .200" wide above the rings which is liable to touch the cylinder bore. Since doing this we have not seen any serious marks on the top band. On the pistons were running Contd. | ||