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).
Engine compression ratios, piston options, and carburettor lubrication.
| Identifier | ExFiles\Box 146\5\ scan0361 | |
| Date | 14th May 1940 | |
| Sr. from Rm.{William Robotham - Chief Engineer} Rm.{William Robotham - Chief Engineer}15/ML.14.5.40. B.12.AW. With reference to VA.1/ET.30.4.40. your car is fitted with raised crown pistons. The compression ratio should only be 6½ to 1, which is relatively speaking, low for a Bentley and it is a ratio at which these engines are functioning satisfactorily over here on Pool petrol. If you really wish for a still lower compression ratio you had better fit a set which you have removed from a Wraith car, which will bring you down to 6 to 1. The best oil to use for the pistons of the carburettors is a non-oxidising fine oil, such as 3 in 1, which is used for cleaning shot-guns and rifles. We will try and send you a new brake plunger. Rm.{William Robotham - Chief Engineer} | ||