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).
The testing and performance of 14mm spark plugs in various vehicles.
| Identifier | ExFiles\Box 58\2\ Scan045 | |
| Date | 1st July 1932 | |
| To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Wm. c. SE. WOT. c. RE. E.{Mr Elliott - Chief Engineer} c. Da.{Bernard Day - Chassis Design} EV.{Ivan Evernden - coachwork} HdV. 81812,l. Hs{Lord Ernest Hives - Chair}/Wm.1/ADR.7.32. 14 MM. SPARKING PLUGS For some time past 12 mm. and 14 mm. plugs have been used on light aircraft engines and on motor cycles. We understand that the winners and most of the other competitors in the T.T. Race this year ran on 14 mm. plugs. We have recently been conducting some tests on them. We had one set running in inserts in a standard 25 HP. car on Brooklands. This car conducted as many as 10 consecutive laps all out without any signs of pre-ignition. During the tests, which lasted three days, the plugs gave no trouble whatever. We have been running the same size of plug in all our experimental 25 HP. cars and in CLN-60 the Sales car. In no case have we suffered from a sooted or oiled up plug. Since all these plugs have been running in inserts which might impair their cooling, we consider that we have established that there will be no difficulty with pre-ignition trouble. With regard to oiling up, tests so far show that these plugs have been as satisfactory as our standard 18 mm. in this respect. With regard to mechanical strength, there is no doubt that these small plugs are less robust than the 18 mm. variety but with normal handling they do not seem to give any trouble. We have not yet had one break on our car work. We attach photographs showing various varieties of 14mm. plug which we have at present under test. Conceivably it may be found convenient to utilise this size on Peregrine or Bensport. Perhaps the best of the plugs we have so far struck is the HD.{Mr Hayward/Mr Huddy}14-3 which is the three point Lodge. Hs{Lord Ernest Hives - Chair}/Wm. | ||