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).
Investigation into popping back caused by faulty K.L.G. sparking plugs.
| Identifier | ExFiles\Box 162\5\ img071 | |
| Date | 20th June 1938 | |
| 6001 RM{William Robotham - Chief Engineer}/RC{R. Childs} BY.3/C.20.6.38. RE: K.L.G. SPARKING PLUGS FE.30X(R). 14 m/m.{Mr Moon / Mr Moore} As a result of complaints made by the owner of 3-DL-36, Mrs. Luck, that popping back was taking place in the carburetter, and N. were unable to obtain a solution of the trouble, I arranged with Rm{William Robotham - Chief Engineer}/GWH.{George W. Hancock - Head Chateauroux} that the car should come to Derby. Mx.{John H Maddocks - Chief Proving Officer} and Rm{William Robotham - Chief Engineer}/GWH.{George W. Hancock - Head Chateauroux} were both of the opinion that it was ignition trouble, N. however, was so certain it was either valves or carburation that they completely dismantled the head, cleaned up the valves, and as always some marks are visible on the valve stems, concluded that the trouble was valve sticking - the whole of this effort was unnecessary and wasted. A further attempt to clear the trouble was made by refitting another carburetter which again failed, and in view of this we arranged the car should come to Derby. Mx.{John H Maddocks - Chief Proving Officer} and LA.{L. A. Archer} traced the fault down to the fact that certain plugs were not functioning correctly, they were failing to spark on the points, but were giving a discharge at the upper end of the angular space between the corundite insulator and the body of the plug, the discharge taking place along the surface of the corundite and jumping across at the upper end of the angular space, thus giving delayed firing which resulted in a flame being present when the inlet valve opened, this in turn naturally causes the popping in the carburetter complained of. Mx.{John H Maddocks - Chief Proving Officer} further suggests that it is possible that the trouble which was experienced with this type of plug when it was fitted to the Bentley car had a similar origin, but in the case of the Bentley where leaded fuels were being used, it was lead which was deposited on the corundite surface, which in turn caused a surface discharge before the pressure rose sufficiently to jump the gap; the discharge took place again towards the upper end of the angular space. The suggestion is that since with the Bentley car 'missing' did not apparently take place, the car seemed to lose power only, and its maximum speed was found about 70 miles per hour. It would appear that similar conditions were prevailing as those described above, as obviously the result obtained would be that of a strongly retarded ignition on the individual plugs, which were affected. It is suggested that an investigation following this up might be certainly worth while. BY.{R.W. Bailey - Chief Engineer} [Handwritten note in the right margin]: We cannot reproduce this condition. Our views are that over oiling of the Engine caused badly fouled the plugs and this caused missing Rm{William Robotham - Chief Engineer}/Bc. | ||