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).
Technical report on weak rollers, test results, and potential causes of failure in Wraith and Bentley chassis.
| Identifier | ExFiles\Box 153\1\ scan0237 | |
| Date | 3rd April 1939 | |
| -2- withstood this load, and were satisfactory on magnetic crack test. The proportion which passed this test was so small, approx. 10%, that the conditions were changed to 50% overload. About 60% are passing this test. The following conclusions can be drawn from the above test results and facts. (a) The rollers delivered within the last six months are greatly inferior to the original samples on which they were standardised. (b) The deliveries during the last month contain a much higher proportion of dangerously weak rollers than do deliveries of 4/6 months ago. (c) Isolated examples of weak rollers probably exist in 'B' Series Wraith as one of the five chassis available was found to have such a roller. (d) We have so far no reason to believe that the whole of Wraith and 'M' Series Bentley chassis should not be under suspicion. (e) The only failures which have occurred to date in normal use have been on chassis which were shipped to the continent. Some time ago a P.III steering gear was found to be wrecked on arrival at Paris coachbuilders and without any road use after leaving the Works. It, therefore, seems that chassis must receive some form of rough treatment during shipment which damages the steering gear. (f) If, as we believe, rollers as weak as some that have been found on Test Department cars, are already in customers hands, the extraordinary lack of failures, apart from shipment cases, indicates that in actual practice a very small overload capacity, say 25% would probably be quite sufficient. One cannot, however, regard with equanimity an overload capacity of less than 100% on such a vital part. Laboratory tests indicate that the cause of the weakness is either wrong material, wrong heat-treatment, or both. The rollers should be S/ZNCR steel (equivalent to S.82) casehardened to a depth of 0.050-0.060. | ||