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).
Letter from Lodge Plugs Limited discussing spark plug thread sizes, materials, and suitability for different aircraft engines.
| Identifier | ExFiles\Box 162\6\ img361 | |
| Date | 7th June 1940 | |
| Telephone, 2076 RUGBY (2 lines) Established 1904. Telegrams, 'LODGE, RUGBY' 6002 Elect. Lodge Plugs Limited. Rugby. W.A. Robotham Esq., Rolls-Royce Ltd., DERBY. Our Ref. BH/EW. Date 7 June 1940. DIRECTORS J.{Mr Johnson W.M.} ALFRED HOPPS, Chairman. BERNARD HOPPS, Managing. F.{Mr Friese} BRODIE LODGE LIONEL LODGE All letters must be addressed to the Company, not to individuals Dear Robotham, Many thanks for your letter of the 5th inst., together with copy of Mr. Olley's letter re spark plugs for American aircraft engines. I do not agree that 18 mm. thread is essential for ceramic plugs. On the contrary we are using the same ceramic insulator in the 18 mm. as we are in the 14 mm. plug. The only objection that I can see to the use of the 14 mm. plug is the necessity of using a high grade steel to give the thread strength as specified by the Air Ministry, the use of this steel necessitating the threads being ground or hobbed. For our commercial 14 mm. plug we have always used a lower grade steel which can be readily machined and we experience no complaints of thread fracture. The B.G. plug may be satisfactory in softer type American engines, but I understand it is not a plug to stand up to conditions of our later type engines. The face-firing ceramic plug is of course a very old idea but never met with much success. The recent introduction of the silver core in ceramic plugs has enable us to meet both the severe heat conditions and the lead deposit encountered in present aero engine conditions. This has been proved by the success of the Lodge RS{Sir Henry Royce's Secretary}5. plug in Rolls-Royce engines. I want to thank you for bringing this letter to P.T.O. | ||