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).
Modifications to cam design to prevent valve float and spring breakage at high speeds.
| Identifier | ExFiles\Box 43\3\ Scan096 | |
| Date | 20th December 1926 | |
| To E.{Mr Elliott - Chief Engineer} Hs.{Lord Ernest Hives - Chair} To RG.{Mr Rowledge} BY.{R.W. Bailey - Chief Engineer} from R.{Sir Henry Royce} c. to BJ. Wor.{Arthur Wormald - General Works Manager} X4003 R1/M20.12.26. RR. F.10. VALVES LEAVING CAMS. X.3822 X.4003 Mr. Lovesey's very able reports give two somewhat different diagrams. The first one the roller and valve moves further than the height of the cam, in the latter the roller only leaves the cam on the closing stroke. Probably both are right at different speeds. I think however the second is the real one we are interested in. One thinks that we ought to alter the shape of the cam to give varying acceleration, somewhat as shewn in diagram blow :- SEE ORIGINAL FOR SKETCH. Inlet only. Object : To save time and let the valve spring follow the cam at higher speeds proportionate to the spring force. E.{Mr Elliott - Chief Engineer} will make a guess and calculated estimate of the allowance, to make for - (1) The altered spring rating, suggesting a symmetrical but more pointed cam i.r. sloping deceleration. and (2) The effect of the air pressure, suggesting a greater margin of spring pressure in the closing stroke, and an unsymmetrical cam giving more time for closing by spring. I discussed this with E.{Mr Elliott - Chief Engineer} but Mr. Lovesey's first diagram made me think there was no room for such finesse, but I now think we might allow say 10% in each case. I cannot believe it would do any harm, and might do much good. Present cams seem to demand 30 to 60 lbs. for 2400 revs. Above cams may only demand 25 to 50 lbs. for 2400 revs. There is no mystery why the springs break, if roller is thrown higher than cam, but with low stressed springs convolutions can become choc-a-bloc witout overstressing the spring. | ||