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).
Specifications for aero engine sparking plugs, including bodies and gland nuts.
| Identifier | ExFiles\Box 58\2\ Scan106 | |
| Date | 1st April 1934 guessed | |
| -2- 3. Modifications. No deviation from the materials or modifications to the design or construction of any sparking plug which has received provisional or final type approval may be made without first being submitted in writing for the approval of the Director of Technical Development. 4. Dimensions. All sparking plugs for aero engines shall conform to the dimensions in Figures 1 and 2 shewn on drawing No. E. {Mr Elliott - Chief Engineer} & I. 4176 except as otherwise agreed in writing by the Director of Technical Development. 5. Sparking Plug Bodies. (a) Sparking plug bodies shall be made in steel not inferior in quality to the B.S. Specific S.1. (latest issue), or as agreed by the Director of Technical Development, and shall be submitted to an approved anti-corrosive process. If the external threads are not fully protected in the finished state, they are to be coated with rust preventative to D.T.D. Specification No.121B. (b) The dimensions and form of screw thread on the body of the sparking plug shall be in accordance with B.S. Specification No.E.9. and approved gauges set to the dimensions given in that Specification shall be used to test the full, effective and core diameters of this thread on each sparking plug body. (c) The shape of the radius at the shoulder is optional, but shall not be less than .010". The screw thread of full form and standard dimensions must continue to within 3/32" of the shoulder. (d) The diameter at the point where the thread runs into the shoulder on the sparking plug body must be within the following dimensions, viz. 18 mm. minimum, 18.5 mm. maximum. (e) Sparking plug bodies may, at the discretion of the manufacturer, be knurled. 6. Gland Nut. (a) The gland nut if made in steel shall be treated with an approved anti-corrosive process. (b) The thread of the gland nut and the inside thread on the body which receives it shall be of Whitworth form 24 threads per inch and the depth of the screwing shall be such that there will be at least 5 1/2 threads in engagement when the gland nut is screwed up tight. (c) The gland nut hexagon shall be a standard 3/8" Whitworth in accordance with B.S. Specification No. 32/1927. (d) Gland nuts must be interchangeable in the steel bodies and the clearance between the effective diameter of the gland nut and the body shall not exceed 0.008 inches. | ||