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).
Engine tests to improve slow running by adjusting tappet clearances and testing various ignition coils.
| Identifier | ExFiles\Box 101\3\ scan0067 | |
| Date | 1st May 1937 | |
| (2) Tests were carried out to obtain the best slow running with minimum tappet clearances; reducing exhaust duration rather than the inlet. The best result was inlet at .010 and exhaust at .015". A new ignition coil taken from production and interchanged with 25.G.V. gave constant hesitation and misfiring when idling light and still lumpy under load at 4 M.P.H. This hesitation or incomplete combustion at low speeds, was constant throughout the tappet clearance tests and was cured by fitting a new type coil supplied by Rm{William Robotham - Chief Engineer}/Wst. (D.75673). The standard coils do not begin to fail until warmed up through contact with engine heat. The standard Stromberg D.C.42 carburettor is good for idling but progression to main has a weak bias. The air bleed control is better in this respect than the Phantom III system of supply control and fixed air bleed; as the former operates on both idle and progression equally. A Phantom idle system was reproduced on the D.C.42 or 30 H.P. carburettor, with the result to date of a flat spot on changeover. Ignition coil tests were then carried out as follows , Delco-Remy; new type R.R.D.75673, and Lucas coils are O.K. with plug gaps at .030" normal temperatures, occasional miss at 5 M.P.H. F.T. They all misfire badly when wired up wrong, i.e. input and output. Standard coil and ballast resistance misfire badly on part and full throttle acceleration up to 25/30 M.P.H. at .030" plug gaps. 2nd. standard coil tested with same results. All coils were mounted together and subject to the same temperature conditions. Temperature rises from normal running at 48°C. to maximum of 65°C. after idling for 15 mins. Summary of tests. 1. New ignition governor set at T.D.C.,F.A. | ||