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).
Resume of experience with sparking plug troubles, particularly on the Bentley chassis, using K.L.G. Mica insulated plugs with leaded fuel.
| Identifier | ExFiles\Box 162\3\ img041 | |
| Date | 4th December 1936 | |
| 6000 To Sg.{Arthur F. Sidgreaves - MD} from Rm{William Robotham - Chief Engineer}/Wst. c. to Hs.{Lord Ernest Hives - Chair} E.{Mr Elliott - Chief Engineer} Hy.{Tom Haldenby - Plant Engineer} c. to Mx.{John H Maddocks - Chief Proving Officer} Hd.{Mr Hayward/Mr Huddy} EP.{G. Eric Platford - Chief Quality Engineer} c. to Sr. Br.{T. E. Bellringer - Repair Manager} K.{Mr Kilner} SPARKING PLUGS FITTED TO OUR CAR ENGINES. In view of the troubles experienced with sparking plugs, particularly on the Bentley chassis, we give below a resume' of our experience to-date. The complaints can briefly be summed up as being due to - (a) Low speed "pick up" misfires. (b) Early ignition at high speeds causing 'popping' in the carburetter. These troubles have all occurred with the use of K.L.G. Mica insulated plugs. In the case of (a) all the evidence goes to prove that the misfiring is due to an excessively electrical leakage deposit formed on the surface of the mica insulator when lead fuel is used. This deposit only gives trouble when it combines with carbon and is only evident therefore after the engine has been run slowly on light load for some considerable time. A cure for this trouble would therefore be to fit a plug having a lower heat factor which would run hotter, but care has to be taken to avoid excessively high plug temperatures at high speeds where preignition would cause serious overloading of the engine parts. Experiments are in hand ascertaining how far we can 'hot-up' the plugs in this way. It ought to be stated at this juncture, that there is no evidence available to shew that a Ceramic insulated plug would be immune from this trouble if run too cool in the engine, although we have been told that an unglazed Ceramic surface is less prone to the formation of lead deposit than mica. Until recently we have had absolutely no experience whatever with Ceramic plugs used with Ethyl Fuel. With regard to (b) we have examined dozens of plugs removed from our own and customers' cars with this complaint, and almost invariably we have found one or two plugs per set with a characteristic whitish spot on the insulator surface which under a magnifying glass revealed a broken piece of mica and in some cases a cavity into the mica. continued.. | ||