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).
Letter from the Experimental Department responding to a query about valve seat recessing on a Rapier car.
| Identifier | ExFiles\Box 128\3\ scan0068 | |
| Date | 1st March 1940 | |
| 1360 Experimental Dept. Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation}2/MH.{M. Huckerby} 1st. March, 1940. - Smith, Esq., 55, Albany Park Road, Kingston, SURREY. Dear Sir, In answer to the query contained in your letter (no date) with reference to your Rapier car. It is not clear whether the valve seat recessing is due to accident or design on your part. If it was the latter, then you could produce the same result by setting the tappets at .036. This is assuming that the inlet tappet clearance of .006 marked on your sketch is true for normal and recessed valves. In any case the general effect will be as follows:- Slightly lower compression ratio; the effective valve lift will be reduced; the effective inlet cam duration will be reduced; and it seems that reduction of .030 to the compressed length of the valve springs has caused 'valve bounce', thus your new springs. Assuming that the original springs were fully efficient, the lost poundage could have been regained by putting .030" thick washers beneath the original springs. Anyway, the general effect on performance would almost certainly be as follows:- At low and middle speeds, no measureable difference. At high speeds; loss of power. | ||