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 development and testing of the Bentley 60 unit, detailing issues with the cylinder head and compression ratio.
| Identifier | ExFiles\Box 123\5\ scan0279 | |
| Date | 1st February 1939 | |
| To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} c. Hs.{Lord Ernest Hives - Chair} c. Da.{Bernard Day - Chassis Design} c. RHC.{R. H. Coverley - Production Engineer} c. HPS.{Horace Percy Smith - Experimental Factory Mgr} c. Da{Bernard Day - Chassis Design}/Jnr.{Charles L. Jenner} c. Da{Bernard Day - Chassis Design}/NCS. Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}2/EH.1.2.39. BENTLEY 60 UNIT TEST. We give herewith an up to date report of the development of the B.60 unit and its position relative to the Bentley V unit which can be said to be the outcome of 15 year's work. CYLINDER HEAD. The original power developed on this unit as designed at 6.4 : 1 compression ratio was disappointing in that it was very little different to a Bentley V with the same induction system and compression ratio. In view of the excellent non-detonating characteristic of this unit as a single cylinder it was decided to raise the compression ratio to 7 : 1 in order to uplift the power, and was carried out by machining .070 off the cylinder head face. This immediately ran us into bad detonation and pre-ignition, particularly at 3000 r.p.m. where maximum power could not be held for more than several minutes. If left running the speed would drop to 2000 r.p.m. and develop only about half the normal power. Switching off the ignition when running could be carried out without any appreciable power drop and running would continue for several minutes before finally stopping, an intolerable condition. From past experience we know that the altered compression ratio, from 6.4 to 7.0 : 1 would not Continued. | ||