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 discussing bench test results and potential modifications for sleeveless magnetos to reduce noise.
| Identifier | ExFiles\Box 65\3\ scan0092 | |
| Date | 8th September 1927 | |
| c. Roy.{Sir Henry Royce} c. EY. c. Mailing. CWB X7791 EFC4/T. 8th Sept., 1927. Messrs. North & Sons Ltd., Whippendell Road, Watford. For the attention of Mr. R.B. North. Dear Sirs, We have completed preliminary bench tests of the two latest sleeveless magnetos Nos. 99171/99802, and are now investigating the operation and silence of these machines on cars. The results of the bench tests have been very satisfactory and rather led us to expect that reasonable silence will be secured on the cars. We are writing to you rather earlier than we meant to do because in one of the two cases it was reported (and confirmed by the undersigned) that the contact breaker is noisy and we wonder to what extent the noise might be due to the fact that we have a sharp make instead of an easy make, as suggested by ourselves. Your make and break of these two machines are equally sharp to the extent that a variation of the primary point gap of .004" either way does not produce a variation in the timing of more than 1/4°. Since the limit given in our General Specification is 3° for the break, the cam might be a little less sharp even at the point of break. In regard to the timing of the make, we have suggested that it is not of serious consequence if this timing be altered ± 10° by altering the primary point gap ± .004" from normal, i.e. that we might use a cam allowing the make to take place very gradually, thus assisting in silence and helping to prevent bouncing at high speed. You may have a reason for not doing this, but we can see no reason why it should not be done. We should also be interested to know if you have considered the question of a continuous cam ring as against a built-up cam ring with separate cam pieces. In our opinion this is a useful contributory feature to the silence of the magneto, and probably also easier to manufacture. (Contd.) | ||