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 comparison of ignition distributor designs, focusing on materials and firing intervals with reference to the Liberty distributor.
| Identifier | ExFiles\Box 35\5\ scan 026 | |
| Date | 17th April 1918 | |
| X.3513. Hence the contacts in the Liberty distributor are merely circular brass patches, 3/8" diameter, let into a hard rubber (vulcanite) ring, which is moulded in place in the Bakelite distributor. The rotor carrying the carbon contact is a bakelite moulding. The ignition can be made lighter on our motor than on the Liberty for the following reasons:- The intervals on the Liberty distributor are 22½ degrees and 37½ degrees and the circumferential distance along a hard rubber contact between two adjacent contacts must not be less than certain amount, about 3/4". This gives the minimum distance between two adjacent contacts as 1-1/18", which must be the length of the arc subtending an angle of 22½ degrees on the Liberty engine. This corresponds to a diameter of 5/75". In our case this distance must only subtend an angle of 30 degrees, corresponding to a diameter of 6.32. [handwritten annotation: these dimensions are only approximate] For the experimental ignition they will simply elongate the terminals outwards, as shown in the marginal sketch, to take care of the equal firing intervals. The distributor while on the Liberty has been tested for upwards of 30 hours continuous running at full speed without attention. I think that what saves the carbon contact is that the hard rubber on the track does not soften and begin to wear away, as happened on the Dixie distributor. X.3513. Whilst taking with them about this, an interesting | ||