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).
Calculations and fitting instructions for cylinder lever mechanisms and vacuum pipes.
| Identifier | ExFiles\Box 128\2\ scan0199 | |
| Date | 12th October 1933 guessed | |
| CC.1/5 -5- A lever 17" could not be used on the average car and therefore this must be compounded, using either a relay lever or bell crank, depending on cylinder location. Having now selected the size of cylinder, the stroke required can be found. EXAMPLE FOR CYLINDER HAVING AUTOMATIC CUSHION In diagram 2, the pedal leverage = 12 x 2.75 / 1.25 = 26.4" lever on cross-shaft compounded with 17.1" for the cylinder. Total pedal movement is 3.5" Equivalent piston movement = (3.5x17.1) / 26.4 = .226 say 2¼" To this add 7/16" (for B. size cylinder, ½" for C. size) to account for valve movement and to allow a margin for initial adjustment So that stroke required = 2¼ + 7/16" = 2 11/16" CYLINDER WITH FIXED CUSHION POINT Minimum stroke before cushion, equivalent to C - D Fig.1 = (1.5 x 17.1) / 26.4 = .97" Minimum stroke after cushion C - B Fig.1 plus ⅜" to ensure free thrust race when clutch is "in" = (1 x 17.1 / 26.4) + ⅜" = .646 + ⅜" say 1 1/16" Select cylinder having a stroke before and after cushion at least equal to these figures. Extra stroke does not matter, but the shortest stroke should be used. FITTING UP HINTS (a) Freedom of movement throughout is absolutely essential. (b) The yoke end by which the cylinder is anchored must have at least 1/64" side play. (c) When the motion pin is withdrawn from piston rod fork end, the end of rod should swing up or down quite freely at least ¾" from its working centre line. (d) The fork end must slide freely on lever - check with lever in all working positions. (e) The vacuum pipe connection on manifold must be arranged so that petrol cannot run down into valve. The offtake on manifold should be arranged on top if possible, but if this cannot be done the pipe should start from the manifold in an upward direction. Vacuum pipes must have a clear bore of at least ⅜". ⅜" o.d. copper pipe, 20 gauge, is a suitable size. | ||