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).
Technical memorandum discussing issues with Watford magnetos, comparing their performance and weight to Bosch and Conner models.
| Identifier | ExFiles\Box 4\5\ 05-page175 | |
| Date | 8th April 1921 | |
| To R.{Sir Henry Royce} from EFC. c. to O J.{Mr Johnson W.M.} c. to E.{Mr Elliott - Chief Engineer} X430 EFC9/T8.4.21. X.430 - MAGNETOS - REF: E1/G31.3.21. X2375 X 3916 X4279 X2917 "Have since noticed Watford (standard E6) appear to have their armatures wrongly timed with the break" - Our comments on this are as follows :- If the lever were timed as suggested to get the minimum break speed in the central position, then firing at high speeds in the advanced position would not be obtainable. The top end of the range is fixed by this consideration and our fixing of this agreed with that of the makers. If the magneto were only to be used for slow speed running, some advantage might be gained this way, but we think that the sparking speed would rise much more rapidly per unit of angle on the advanced side of the minimum than on the retarded side, but we will investigate. "We do not want extra weight and cost" - It was put up to the Watford Co. some time ago now to produce a magneto with larger armature and larger safety gap in order to give more capability of firing the engine at slow speed and at normal speed under adverse conditions. This was previous to the magneto bench tests which we have recently carried out." We expect to receive such a sample machine from the Watford Co. shortly. The two magnetos mentioned as the best offered, Robert Bosch and Conner, are the two heaviest on our list being 18.25 lbs and 16.1 lbs respectively, whereas our present standard Watford is only 11.7 lbs. We expect the new Watford to have a weight similar to the Conner. The U.S.A. Bosch magneto which broke down was not the Z.R.6 type, but the smaller B.6 type. The one that had to run at 520 revs. in retarded position was also a B.6. We have so far had satisfactory operation from the Z.R.6. Further, we have recently received information that the B.6 type which broke down was an early one of that type and has since been improved in that respect. "These would appear to show that the EPC. sleeve type Watford would do what was required in this respect. I have pointed this out to Mr. Hives and he has agreed to watch this carefully on the cars which are fitted with Watford Z.U.6 magnetos. | ||