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).
Specification for sparking plug components, markings, and testing procedures.
| Identifier | ExFiles\Box 58\2\ Scan107 | |
| Date | 1st April 1934 guessed | |
| -3- (e) Sparking plug centre and gland nuts, if integral, shall be interchangeable in the steel bodies. 7. Central Electrode Terminal. (a) Terminal adaptors of an approved pattern are to be used for securing the H/T cable to the plug terminal. Spring or loose terminals and clips shall not be used for this purpose. (b) The terminal of the central electrode shall be no. O.B.A. or No. 1.B.A. in accordance with B.S. Specification No.93 and shall be threaded for a length of 9/16" between the securing nut and the radiused portion at the end. Alternatively a ball terminal of the dimensions shewn on Figure 1 and 2 of drawing No.E. & I. 4176 may be used if required. 8. Copper Washers. Each sparking plug shall be provided with a copper washer in accordance with B.S. Specification No.E.9. 9. Marking of sparking plugs. (a) All sparking plugs shall be marked with maker's type letter and/or number. The nomenclature must be as brief as possible. (b) All sparking plugs after acceptance shall be marked with the Tudor Crown 1/8" high and the letters "A.M." 3/32" high. Section 2. General Conditions of Testing. 10. Inspection. All sparking plugs for aero engines are to be to the satisfaction of the authorised representative of the Secretary of State in whose presence the tests are to be carried out when so required. 11. Suitability of Test Plant. The test apparatus, conditions of test, method of recording temperature, spark voltages, etc., must be such as to satisfy the requirements of the Secretary of State. 12. H.T. Supply. Flash-over, dielectric strength and sparking tests under air pressure laid down in Clause 19 will be carried out with H.T. current supplied by a magneto of an approved type running at such a rate of sparking that not less than 15 sparks per second will be applied to the part under test, the voltage to be measured by means of standard ball gaps. 13. Measurement of H.T. Voltage. (a) Measurement of H.T. voltage shall be by means of standard ball gaps, set as follows :- 9,000 volts - 2.2 mm. 10,000 " - 2.5 " 12,000 " - 3.1 " 13,000 " - 3.5 " 15,000 " - 4.15" | ||