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).
Investigation into misfiring on the No. 6 cylinder of Wraith cars, diagnosing the cause as oxidised spark plug electrodes.
| Identifier | ExFiles\Box 162\2\ img015 | |
| Date | 27th March 1939 | |
| Mx.{John H Maddocks - Chief Proving Officer}1/MG.27.3.39 (continued) - 2 - As there had been a few cases of misfiring on No.6 cylinder on certain Wraith cars in service, we next carried out some tests on the H.T.Wiring lay-out. (1) H.T.wire to No.6 cylinder by shortest path from distributor to sparking plug........................... No improvement (2) H.T.wire removed from tube & spaced apart in rubber support brackets. No improvement (3) Reduced length of main H.T.lead by fitting coil close to distributor No improvement (4) Increased length of H.T.lead from coil to distributor ............ No disadvantage Fitting a new set of sparking plugs with .030 gaps effected a complete cure. Reverting to the original set of sparking plugs misfiring occurred. We now had a set of plugs which would function satisfactorily, and another set which would not, the difference apparently being due to oxidation of the plug electrodes. Tests in the plug compression chamber showed no difference between the two sets of plugs. Assuming the difference was due to oxidation, this would not be shown up in the plug tester, but an oxidised plug will have the effect of giving a delayed weak spark. Delayed firing was not confined to any particular cylinder. This was proved by changing one oxidised plug at a time. The trouble was temporarily overcome by the use of feelers to check the plug gaps, which apparently cleaned the | ||