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).
Confirming the valve sizes for the 20 HP and Phantom models.
| Identifier | ExFiles\Box 66a\2\ scan0067 | |
| Date | 9th March 1928 | |
| E.{Mr Elliott - Chief Engineer} Hs.{Lord Ernest Hives - Chair} from R.{Sir Henry Royce} BY.{R.W. Bailey - Chief Engineer} c. to B.J. Wor.{Arthur Wormald - General Works Manager} 48660 R1/M9.3.28. X. 5060 X. 8060 20 HP. & PHANTOM VALVE SIZES. I agree to LeC. 2523 : Phantom. Exhaust 1.700 ) Inlet 1.900 ) Bore of seat. 20 HP. Exhaust 1.250 ) Inlet 1.350 ) " " " Material of valves may be different for exhaust and inlet as may be advantageous for hardening the ends, ease of forgings, and machinery and cost. R.{Sir Henry Royce} | ||