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).
Adjusting valve timing and tappet clearance to control engine roar.
| Identifier | WestWitteringFiles\K\September1923\ Scan54 | |
| Date | 20th September 1923 | |
| R.R. 493A (40 H) (SL 42 12-7-23) J.H., D.{John DeLooze - Company Secretary} EXPERIMENTAL REPORT. Expl. No. X.4229 REF: HS{Lord Ernest Hives - Chair}3/LG20.9.23. but would roar with early timing, we should be able, according to the indicator theory, to bring on the roar with standard timing by reducing the clearance of the inlet valve tappet, and increasing that of the exhaust. This was confirmed in practice. Again, when firing, the restriction of the exhaust egress is mainly responsible for the positive pressure in the cylinder. (Fig.G.1.) Under the same conditions as the previous check we should be able to bring on the roar by adjusting up the inlet tappet and increasing the restriction of the exhaust discharge instead of lowering the exhaust tappet, that is merely building up the positive pressure in another way. The object of closing up the inlet tappet is to make the inlet valve open as early as possible and so get the full benefit of the extra positive pressure. The latter was also confirmed practically. The standard timing on production cars appears to make the inlet open 12½° after T.D.C. The timing we have referred to as standard in this case, therefore, is too early. Diagrams sent to R.{Sir Henry Royce} only. | ||