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).
Comparative analysis of original, modified, and proposed hydraulic rockers for a 3½ Litre Bentley engine.
| Identifier | ExFiles\Box 88\4\ scan0112 | |
| Date | 7th September 1934 | |
| 3½ Litre Bentley. 7th September, 1934. Comparative Figures - Hydraulic Rockers. TABLE: Row 1 Header: A Original Ex 14182, B Modified Sk 4324, C Proposed Sk 4476 Equivalent weight of rocker at valve-grams: A 67.5, B 42, C 35 Equivalent weight operated by valve springs-grams: A 251, B 197, C 190 Maximum speed without valve bounce-RPM: A 4640, B 5240, C 5330 Rocker Section - inertia moment Ixx - in4: A .00247, B .00247, C .0050 Rocker Section - modulus Ixx/y - in3: A .0093, B .0093, C .0157 Fulcrum Bearing Pressure - lbs/sq.in.: A 790, B 785, C 835 Assumptions. 1. In the absence of detailed information on the weights of individual parts comprising the valve gear, the total weight of 251 grams (R.R. letter 28.7.34) for the original experimental rocker and lightened valves, has been accepted as a basis for the calculations. 2. Scheme A in the table above assumes the light-alloy push-rod HS{Lord Ernest Hives - Chair} 1453, while schemes B and C assume push-rod (and tappet) return springs as shown in Sk 4394 of sufficient strength to return the parts at the maximum speeds permitted by the valve springs. Lightened valves HS{Lord Ernest Hives - Chair} 1450, 1451 are assumed in all the schemes. 3. Valve bounce with the standard (non-hydraulic) valve gear occurs at 4900 RPM with an equivalent weight of 225 grams. The maximum negative inertia force is then 86.5 lbs. 4. Valve bounce with the proposed rockers will occur when the inertia force under spring control equals 86.5 lbs. This leaves an allowance of 15.5 lbs or 17.9% for valve-guide and rocker friction. 5. The rocker section taken above refers to a section .65" from the rocker fulcrum on the push rod side, and represents approximately the most highly stressed point. 6. The fulcrum bearing pressures are worked out for the point of maximum positive acceleration at 5000 RPM. P.S. Drawing Sk.4477 shows a light-alloy plug for the ball stop. If, for the sake of durability in maintaining the ball-lift clearance, it is found desirable to use steel, the equivalent reciprocating weight at the valve is increased by 2 grams, and the bouncing speed reduced by 30 RPM. p.p. FRANK B. HALFORD. TECHNICAL ASSISTANT. (E.{Mr Elliott - Chief Engineer} S. Moult) | ||