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).
Tests carried out to determine magneto requirements for the 40/50 engine, focusing on spark plug polarity.
| Identifier | ExFiles\Box 4\5\ 05-page187 | |
| Date | 5th May 1921 | |
| To R.{Sir Henry Royce} from Hs.{Lord Ernest Hives - Chair} c. OJ. BN.{W.O. Bentley / Mr Barrington} E.{Mr Elliott - Chief Engineer} c. Da.{Bernard Day - Chassis Design} EY. EP.{G. Eric Platford - Chief Quality Engineer} c. PN.{Mr Northey} EWT. for R.R.Inc. X.30 Hsl/LG5.5.21. MAGNETO REQUIREMENTS FOR 40/50 ENGINE. X.430. X.699. X.2375. We have carried out a number of tests with a 40/50 engine on the bench and also with cars on the road in order to ascertain what are the requirements for a magneto for our 40/50 engine. Test carried out on 40/50 engine on the bench. We first of all arranged the engine with two induction pipes and a carburetter for each three cylinders. This allowed us to run the engine on three cylinders and to use the other three for compressing air only. We found under this condition with a standard E6 Watford magneto that the magneto spark would prefer to jump the safety spark gap set .300" rather than jump the .018" gap at the clean sparking plug points. During these tests we proved that there is a very considerable difference in the sparking of a magneto according to the polarity of the spark at the plug. When the central electrode of the sparking plug is positive, the spark will prefer to jump the safety spark gap rather than the clean plug set at .018". If the central electrode is negative, the spark points can be set at .032" in order to get the same conditions of sparking at the safety gap. This point as regards the different results of sparking with different polarity was proved by EFC. on our battery ignition. These tests shew that a standard car with the standard Watford magneto and plugs set at the standard gap .020", the spark will | ||