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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).
Magneto testing, detailing issues with contact wear, noise, and a comparison of gear materials.

Identifier  ExFiles\Box 65\3\  scan0222
Date  23th May 1928
  
-2- Contd.

this will have an effect on the low speed sparking. EW6 magneto No.99802 on one of our experimental cars 9-EX, has only run 3856 miles, but the contacts have worn down 50%. It appears that with suitable relation of magnet size and armature winding and condenser, the use of tungsten points is possible, e.g. Lucas magnetos with tungsten points pass our specification of performance with possibility of increased margin, as a result of slight further modifications.

In this connection may we refer you to the Paper of Mr. A.P. Young of Messrs. Young and Griffiths read before the Institution of Automobile Engineers, which will be found on p.544 et.seq. in the Proceedings of the Automobile Engineers for the Session 1926-7.

(6) In regard to the details of test of the special machine No.106012, this magneto having passed our production test, which includes all the usual items which we expect to be right on a magneto, was handed to our Test Dept. Having been run by them on three different chassis for approximately 150 miles, it was pronounced satisfactory both for electrical performance and noise, but on continuing to run the magneto further, it developed a bad knock, i.e. after running a further 95 miles, making 245 miles in all. The machine was then returned to us. In order to find out whether the knock was anything to do with the contact breaker, we arranged to put this on an experimental car with the spark gap in such a manner that the magneto would be normally functioning as regards its armature, but with the distributor removed. The result was that the magneto was found to be O.K. for noise, but it was also O.K. when the distributor was replaced, as if the removal and replacing of the gear wheel had got rid of a small particle of dirt or swarf in the gears. This magneto is now on one of our experimental cars and is so far continuing to give satisfaction.

Further to this, of four machines which passed through the production channels to the Test Dept., two have developed similar knocking after about 100 miles running. The undersigned has suggested that these two machines be returned to you for your inspection.

You will remember that you previously used a bakelite pinion and aluminium gear wheel. We are not clear whether you have tried the combination of steel pinion and bakelite gear, as so far as our experience goes, this seems to give the greatest satisfaction.

Yours faithfully,

FOR ROLLS-ROYCE LIMITED.

Seen B 23-5-28
Noted by hmp 24/5/28
  
  


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