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).
Investigating the cause of excessive wear on a contact breaker for Car 7 CA.
| Identifier | Morton\M11\ img047 | |
| Date | 8th July 1917 | |
| To EH. } from Oy. EFC. 7CA. New C/B ORIGINAL OY2/B30:5:17.2 RECEIVED D JUL 1917 8 X.2823 Re Car 7 CA. X 682 With reference to the contact breaker on 7 CA. would you please inform me whether you have found any reason for the great wear of the fibre on this contact breaker. We ran this at 6,000 revs. on the bench for periods of up to 13 hours non-stop without any measurable wear, and I think it is important to find out why it has worn so badly with merely intermittent running, very seldom exceeding 1500 revs. There are one or two possible reasons - (1) That the pressure on the platinum points was too great. The pressure on the platinums for a car magneto which never has to run above about 3,000 revs., would be quite sufficient at 1 lb. or even about 18 of a lb., as the centrifugal force will never be enough to lift the platinums off. If the spring was set up to say 1 1/4 or 1 1/2 lbs. when the contact breaker was sent away, this would account for the wear, because the load on the platinums would not be counterbalanced by the centrifugal force, and therefore the rubbing on the fibre block would be severe. At the same time I cannot explain the rapid wear unless - (a) The cam was dry or rough, or the fibre was uncompressed. I do not think that one can explain it by the rocker being of steel or unbalanced, although the good results were actually obtained with a duralumin rocker. I do not know what material was actually used on 7 CA. We should like to know whether the cam surface had a drop of oil on it when the car left the Works. (Contd.) | ||