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).
The performance and reliability of Wraith and Ph.III type rollers, detailing service failures and rig test results.
| Identifier | ExFiles\Box 153\1\ scan0277 | |
| Date | 20th April 1939 | |
| -2- RM{William Robotham - Chief Engineer}/FJH.{Fred J. Hardy - Chief Dev. Engineer}11/MH.{M. Huckerby}20.4.39. The outer roller of the Wraith type is therefore as strong as the Ph.III type F.89447, while under fatigue conditions the balls and the ball track on the inner race are slightly weaker. The present Wraith type roller has been fitted to all Experimental Wraith chassis throughout their life and also to the 'M' Series Bentley, O.B.IV. No failures have occurred. The roller on O.B.IV has now completed 45,000 miles and during the French test was involved in an accident which indented the ball tracks but did not result in failure. We anticipate that, given correct material and treatment, the Wraith and Bentley roller will be reliable in service but that the margin on the bearings is no more than necessary. Up to date on customers' cars we have had 9 failures of the 0.250 balls in 25/30 H.P. rollers and 40 failures of the 0.187 rollers in the Ph.III type. We attach a tabulated summary of the results of our rig tests on the 25/30 and Ph.III types of roller. RM{William Robotham - Chief Engineer}/FJH.{Fred J. Hardy - Chief Dev. Engineer} | ||