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 to North & Sons Ltd. regarding noise tests on EW6 magnetos and issues with cams and armature.
| Identifier | WestWitteringFiles\R\2December1927-February1928\ Scan057 | |
| Date | 13th December 1927 | |
| COPY 13th December, 1927. EFC/T. Messrs. North & Sons Ltd., Whippendell Road, Watford. Dear Sirs, Further to our letter EFC3/T. of the 12th inst. we have now done a little work on the very latest type EW6 magneto No.100081. Our impression is that you have provided us with special cams (with correct timing) on this last machine, but not on the previous one No.100080 which has now gone to France on the car. Last night my assistant made a number of tests when all machinery was quiet and he very definitely proved to his own satisfaction that there was a distinct noise at make in all cases, but that this was reduced by the slow make which we think you have provided on the cams fitted to this particular magneto (No.100081). One method of proving this point was to reverse the cams in the cam ring with (in this case) the make taking place sharply and the break slowly. There was found to be a considerable increase in the noise of the machine generally with the cams this way round. This was also confirmed by the reversal of the original short experimental cams which you sent us for the same purpose. In the case of these short cams we confirmed that .004" variation of gap corresponds to 10° variation of break, this being the amount that we had suggested, and we think that the cams on the machine will have a similar variation. A further point my assistant arrived at is that you appear to run this armature with a very small air gap because he considered he discovered that the armature is actually (in this instance also) knocking the pole pieces, or knocking in the bearings, in each of two positions of the revolution in which the magnetic traction suffers the greatest momentary variation. At any rate, under certain conditions, there was a considerable knock emanating from the machine which would disappear upon short circuiting the armature. Contd. | ||