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 the exhaust system and the development of the pilot jet and control system.
| Identifier | ExFiles\Box 81\2\ scan0170 | |
| Date | 7th October 1924 | |
| Oy3-E-10724 -4- October 7, 1924. (5) Exhaust System. (cont'd) Exhaust boxes. We have now lengthened the front box forward, see print A-6020, and also the rear box, (print A-6091) giving a total increase in volume of the exhaust system of 7% compared with standard. (6) Pilot Jet and Control. (See prints #6). As originally made this was combined with the shutter control in an instrument board fitting, as used on the 20 hp. for shutter control. The control was by wire cable as on 20 hp. It was considered that this scheme is absolutely free from rattles and errors in lining up at coachworks etc. The appearance of the fitting on the board was criticized however because of "cluttering up" the board and being out of keeping with our present neat arrangement of circular instruments. The appearance of cables under the bonnet was also unsightly. The modified scheme with levers pivoted behind the instrument board and operating levers exactly similar to steering column controls, is shown in accompanying prints. Standard control rods (which in practice give no trouble from rattling) are used throughout except on control to shutter where a straight wire is used (length too great for rod). The appearance under the bonnet is improved by taking the control rod to the pilot jet horizontal instead of on an angle. A stop is provided on the pilot jet for the closed position. The Derby type pilot jet is used with 1 in 4 taper cock as instructed by Mr. Royce. The operation of this on test has been very satisfactory. The extra oil is held on while pilot jet is in operation. This has eliminated the "cold-knocking" through oil being washed off the cylinder walls, which is difficult to avoid in cold weather on standard cars. Pistons at end of run are in remarkably perfect condition as regards lubrication and bedding showing dull white bearing surfaces without high spots. Carbon accumulation in two runs of 5000 miles each is only a very thin layer. We believe the throttle and the extra oil opening with the pilot jet helped this condition. No hand work was done on the pistons in assembly or later. Many brands of gasoline were used. | ||