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).
Valve gear development, detailing issues with valve springs, rockers, and camshaft chain drives, including a table of seat loads and stresses.
Identifier | ExFiles\Box 113\5\ scan0211 | |
Date | 13th February 1939 guessed | |
-3- The high accelerations involved, and the high lifts necessitated very powerful double valve springs, bounce setting in at about 4000 RPM if single springs only were employed. A number of spring failures was experienced, and two rockers fractured on the tension side of the boss, parallel to the rocker shaft. Seat loadings were very high, and it was decided to try another cam-shaft, with lifts reduced as shown at the bottom of the above table. No work was actually carried out on the shaft, as development was discontinued on the engine, but it would appear a good jumping off point, if the job were ever taken up again. Seat loads and stresses are shown in the following table:- Valve. Spring. LOAD. Stress. Valve Valve Closed. Open. closed. Open. B 111. Inlet. - 47.0 108.0 37.000 85.000 Exhaust. - 47.0 108.0 37.000 85.000 B 60 Inlet. Outer 39 106 28.700 77.400 Inner 10.6 29 25.800 70.000 Exhaust Outer. 47.0 108 37.000 85,000 O.H.C. Inlet. Outer. 57.0 83.9 47.500 70.000 Inner. 25.00 58.20 29.400 67.700 Exhaust Outer. 60.00 133.5 30.500 67.500 Inner. 20.75 41.45 34.600 68.500 The most troublesome item in the valve gear was undoubtedly the chain drive to the cam-shaft, which had frequency periods at 1100-1300 RPM, 1600-1750 RPM, 1800-2900 RPM 3700-4500 RPM all of which were sufficient to overcome the chain tensions when the spring drive was bolted up solid. Without a chain tensioner, and with the spring drive working the amplitude was so great at 2000 RPM, that the engine could not be run above this speed without a risk of breaking the chain. A series of modifications were now made to the system, and the results are briefly tabulated as under:- | ||