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).
Test report on a 'Silca' sparking plug.
| Identifier | ExFiles\Box 33\3\ Scan161 | |
| Date | 9th September 1921 | |
| CJ. from Hs.{Lord Ernest Hives - Chair} X1812 C. Hs{Lord Ernest Hives - Chair}2/LG14. 9. 21. REPORT ON "SILCA" SPARKING PLUG. The tests on this plug were carried out on a single sample plug sent to us by CJ. We have run this plug for 30 hours on a 40/50 engine on the Test Bench, and also 250 miles on a car on the road. After this length of run the plug failed owing to the spark short-circuiting on the inside from the centre electrode to the interior of the body of the plug. At the point where the shorting occurred, the length of insulation is less than we think is necessary. Our criticisms against this plug are as follows:- 1. The plug failed owing to the high tension spark shorting from the centre electrode to the interior of the body of the plug. This only occurred after the plug had been running for 30 hours. If we took the plug apart and cleaned it, the plug was alright for another period. In our opinion, however, the leakage length allowed on the insulators is insufficient. 2. There is no means of adjusting the sparking plug gap. We consider this is an essential feature on plugs for our chassis. We usually run with .020" gap on Magneto and .030" gap for battery. We consider that if the plug was machined accurately enough to provide the correct gap, this gap would not remain constant throughout the life of the plug because, not only would the edges of the serrated points burn away, but after the plug had been cleaned a number of times, one would anticipate the gap to increase. We think there are some very good features on this plug. Firstly, using the quartz insulator is an excellent idea. We have not, however, been able to appreciate the claim that the colour of the explosion can be seen. We admit that if the engine is run in the dark, one can see the flash of the contd:- | ||