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 the cause of Bentley sparking plug misfiring, theorized to be caused by lead oxide deposits.
| Identifier | ExFiles\Box 58\2\ Scan219 | |
| Date | 16th August 1935 | |
| To Hd.{Mr Hayward/Mr Huddy} c. to K/KC. c. to EP.{G. Eric Platford - Chief Quality Engineer} Bentley Sparking Plugs. We have been for some time endeavouring to find the cause of Bentley sparking plugs misfiring. In the majority of cases plugs which have been returned to us for examination have been found to be electrically sound and have been confirmed to be so by tests on Experimental Bentley chassis. No-one has yet successfully demonstrated to us a Bentley chassis which is misfiring badly due to sparking plugs. Some time ago when K.{Mr Kilner} were complaining of these 765A plugs, we took down several sets of plugs returned by them as faulty and requested these to be fitted to a car in order to demonstrate the trouble. Two sets not disturbed in any way were fitted and the cars taken out on the road, but no misfiring could be produced. We are not suggesting that the plugs are not faulty in some way, but unless we can have some more definite information and can actually catch the plugs misfiring so that they can immediately be examined, our investigations will be incomplete. Our theory is that when used with leaded fuel a slight build up of lead oxide deposit inside the plug, with the gap slightly enlarged, causes the spark to pass from the end of the copper tube surrounding the central electrode to the body instead of at the plug points. Messrs. K.L.G. have produced a modification in the 765 D plug to overcome this trouble, but as we do not wish to perpetuate this design of rolled mica plug for the Bentley, we have not carried out any experiments with the 765 D but have preferred to experiment with the 850 plug which is of mica washer construction similar to aero plugs. | ||