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).
Comparing the performance and efficiency of various magnetos and suggesting alterations to the standard Watford magneto.
| Identifier | ExFiles\Box 48\3\ Scan103 | |
| Date | 9th April 1921 | |
| X.4210. To EFC. {E. Fowler Clarke - Electrical Engineer} from R. {Sir Henry Royce} c. to CH. c. to Wpr. c. to Ey. c. to RB. {R. Bowen} c. to De. c. to FH. c. to HP. c. to WM. R5/09.4.21. X.430. MAGNETOS. X.2375. X.3916. X.4181 X.3724 X.4216. X.427. X.3917. It will be noticed from Mr. Clerk's figures that the sleeve magneto of the Watford Company is capable of firing in a retarded position at a slower speed than anything offered. Next comes the Conner and the Dixie. The U.S.A. Bosch does not stand our particularly well from any tests we have been able to make. From the utility test the Conner, the Robert Bosch (German) and the Dixie are the orders of efficiency. The present standard Watford is required to run at a good speed to fire regularly (in the retarded position) and we suggest that this is the cause of the dissatisfaction with this machine. Apparently this could be easily remedied by altering the relative position of the armature to the break, so that the minimum speed required for firing is somewhat behind the central position, i.e. corresponding to the usual position of the control lever for slow speeds. The angular range of advance we think need not be quite so great with any of the magnetos. I suggest that Mr. Clark takes the result of these tests to the Watford people, and induced them to alter one of their present standard magnetos as suggested above so that the sparking speed of 150 revs. is obtained somewhere between the central and retarded position. It would be as well also to alter the length of the safety gap to 8½ mm. Certainly it looks as though 8 mm. should be the minimum for the safety gap. In criticising the speed of sparking 5 miles per hour would be about 175 on the engine when the magneto will be running etc. We cannot believe that it is necessary to expect the engine to run so slowly as this without the battery ignition. We think the people who run their cars without both ignitions are foolish and wasteful of petrol. I suggest that we do very slowly with regard to U.S.A. Bosch machine in England as it will be noticed from Mr. Clark's test that the second machine tested at the makers range of control required in a retarded position, the highest speed of any magnetos, namely, 530 - see sheet A2 dated 23.3.21. A third machine broke down on high tension brush. It is not quite clear what this means. Therefore, of the three American Bosch machines we tested only one is really satisfactory. R. {Sir Henry Royce} R.M. No.31,180. (T) (R) H & C Ltd., 21-12-20-100 | ||