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).
Failure of a Bentley ignition system and proposing material and design changes to the make and break arm bushes.
| Identifier | ExFiles\Box 163\7\ img226 | |
| Date | 16th December 1933 | |
| To Sg.{Arthur F. Sidgreaves - MD} from E.{Mr Elliott - Chief Engineer} / WST 86120. E.10/HP.16.12.33. c. Wor.{Arthur Wormald - General Works Manager} Hs.{Lord Ernest Hives - Chair} By.{R.W. Bailey - Chief Engineer} Sft.{Mr Swift} Hs{Lord Ernest Hives - Chair}/Wst. By/RB.{R. Bowen} re Bentley Ignition. Replying to your memo Sg.{Arthur F. Sidgreaves - MD}1/E.15.12.33, I note the further failure of the make and break arm seizing on the open car B.I.AE. and I think that immediate steps should be taken to open out all of these bushes to give the desired slack. Investigation shows that the bakelite bushes were put on the pins a very nice fit with only ¼ thou. slack as you will see from Hs{Lord Ernest Hives - Chair}/Wst's report, and that this ¼ thou. slack can be taken up by prolonged heating at 80ºC equivalent to the conditions arising in operation on the engine, and also by soaking in water under conditions which we do not think would ever arise. This material is as NON hygroscopic as any substance we can find suitable for the purpose, and we do not think that any failures will occur from this cause if we have the requisite slack in the bearing. The present specified size of the pin is .155 minus ¼ and of the hole in the bush .156 plus 1. We are increasing the hole size to .157 plus 1, and we recommend that JLE{J. Lee Evans - Chassis Test Manager} be supplied with a reamer of this size to open out all the bushes on the demonstrators and that production chassis be similarly treated. This will bring us into line with recognized practice, for example, we find aero magnetos running with a slack of 3 thou. on the make and break bakelite bearing. We are proposing also to immediately standardize the chromium plated pin based on the recent 10,000 mile test, and we are putting in hand a modification to the pin fixing with a view to trying experimentally these pins made in hard drawn bronze as we think that from the point of view of corrosion the bronze pin is a safer proposition than the chromium plated steel. We are still of the opinion that a bakelite bush is better than a bronze bush for the make and break lever owing to its greater independence of the conditions of lubrication, but we are going ahead to obtain a better form of bakelite, and one of the samples we are testing is made from a material impregnated with graphite. | ||