Increasing the inlet and exhaust valve sizes for the Phantom III 4-port head, including a comparison table of valve specifications for various models.
| Identifier | ExFiles\Box 93\4\ scan0023 | |
| Date | 17th October 1935 | |
| x319 R l.e. Smith E {Mr Elliott - Chief Engineer} /JNR. {Charles L. Jenner} 1/HP.17.10.35. BY. {R.W. Bailey - Chief Engineer} (struck through) c. RHC. {R. H. Coverley - Production Engineer} (struck through) c. Hs {Lord Ernest Hives - Chair} /Rm. {William Robotham - Chief Engineer} re Phantom 3 - 4-port head. Referring to Hs {Lord Ernest Hives - Chair} /Smth.3/KW.8.10.35, we agree to increasing the inlet valve to 1.5 diameter and the exhaust valve to 1.3. We have made an amended drawing - LeC. 4765 showing the valve centres spread but keeping the push rods in the same position. This means making a new set of rockers for this particular engine. The large holes in the gasket are increased in size owing to the carving away of the combustion space to permit of the threading for the valve inserts. | | 25 HP. | Bentley. | Spectre(Codename for Phantom III) 4-port. | 25-29 HP. | Large Bore Bentley. | |---|---|---|---|---|---| | Inlet Valve. | 1.35 | 1.4 | 1.5 | 1.5 | 1.6 | | Valve area. | 1.43 | 1.54 | 1.767 | 1.767 | 2.01. | | % of Bore. | 17.2% | 18.5% | 21.4% | 18.4% | 20.7% | | Exhaust Valve. | 1.2 | 1.3 | 1.3 | 1.3 | 1.4 | | Valve area. | 1.13 | 1.32 | 1.32 | 1.32 | 1.54 | | % of Bore. | 13.6% | 15.9% | 15.9% | 13.8% | 16% | E {Mr Elliott - Chief Engineer} /JNR. {Charles L. Jenner} LeC.4765 herewith. | ||
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).