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).
Engine valve bounce, induction system, and slow running performance issues.
| Identifier | ExFiles\Box 124\1\ scan0177 | |
| Date | 29th June 1939 | |
| -4- VALVE BOUNCE - Cont'd.{John DeLooze - Company Secretary} Incidentally, the actual closed position length of the EB.4678/9 springs is 1.615 as against 1.575 stipulated on the spring drawing. In consequence of the EB.4678/9 being unsuitable the unit is now fitted completely with the Ph.III adapted springs. INDUCTION SYSTEM. The distribution on 1.75 bore manifold, which has the large hot-box coupled with the small Duplex downdraught Stromberg AA.{D. Abbot-Anderson}25 carburetter, is reasonably good throughout the range, except at low speeds full throttle when there is a tendency to "load up". If after running at full throttle low speeds, the throttle is closed down, the mixture becomes temporarily very rich due, presumably, to wet unvapourised petrol being sucked into the cylinders. Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation} has this job in hand and investigations are being made in respect of - (a) reduced bore manifold, (b) reduced internal capacity of hot box, (c) increased heat on manifold and (d) Buick type of manifold in respect of shape and disposition. SLOW RUNNING. On the bed the idling was good and even at 250 R.P.M. under conditions of normal .010 tappet clearance, TDC. std. ignition setting and Champion N.A.10 spark plugs. This is not confirmed, however, on the road unless the tappet clearances are opened up to .015 to further reduce the overlap. Based on this result first obtained some time ago, camshafts are nearing completion having less overlap by alteration of the angle between the exhaust and inlet cam forms. We anticipate this will give the necessary satisfactory idling and also assist in solving the reason why in this chassis the long duration camshaft EB.4105 is as good as, if not better than, the short duration shaft EB.4512 with which the unit is fitted. | ||