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).
Borg & Beck clutch failures for Bentley during endurance testing.
| Identifier | ExFiles\Box 129\3\ scan0022 | |
| Date | 6th January 1936 | |
| X 1110 To E.{Mr Elliott - Chief Engineer} c.c. to WcP. c.c. to By.{R.W. Bailey - Chief Engineer} c.c. to Hdy.{William Hardy} c.c. to RK. Hs{Lord Ernest Hives - Chair}/Smth.RD/KW.6.1.36. Borg & Beck Clutch for Bentley. Broken Pressure Plates. We have had two failures of 10" Borg & Beck clutches. Both were on test bed units running under high speed endurance conditions; i.e., 30 mins. at 4,000 r.p.m.; 25 mins. at 4,250 r.p.m.; and 5 mins. at 4,500 r.p.m. Neither failure was suspected until the engine was stripped. (1) A pressure plate was found broken after 95 hours running - see attached photograph. (2) On a second clutch one of the eyebolts which provide the fulcrum for the release fingers was found to be broken close up to the nut after about 20 hours running. In the case of the first failure, the pressure plate was examined for tensile strength and composition and was found to be satisfactory. The theoretical bursting speed is 13,000 r.p.m., and Borg & Beck assure us that they have never known a 10" pressure plate fail even at speeds up to 6,000 r.p.m. The Alvis Speed Twenty engine has a 10" clutch and runs up to 3,500 regularly. Regarding the second failure, the eye bolts were never subjected to the clutch spring loadings. We found that the slots in the cover which locate the release lugs were somewhat worn, and that the spherical seating on the nut of the broken eyebolt was badly scored on the outer edge. We have thus formed the tentative opinion that both the failures have been due to the same cause; namely, that during the prolonged running at high speeds, near the torsional period, the lugs have fidgetted in their locations, causing wear in the edges of the slots and faces of the lugs. This has caused some or all of the centrifugal out of balance load on the pressure plate to be carried by the eyebolts, resulting in failure of the eyebolt in one case and failure of the pressure plate in the neighbourhood of the eyebolt boss in the other. | ||