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).
Failures in connecting rods, reduction gears, and supercharger drives.
| Identifier | ExFiles\Box 143\2\ scan0188 | |
| Date | 24th June 1941 | |
| - 3 - BY/HB.{C. E. Harcombe}5/EIM.24.6.41. Continued : not under-tightened as the bolts may be stretched plastically for a considerable amount without fear of failure and it is considered that failure is due purely to excessive caution in tightening the bolts which results in them being unequally and insufficiently tightened and it should be impressed upon all that stretching of connecting rod bolts of this kind is not dangerous and there should, therefore, be no question of insufficient tightening. As a matter of interest a Brinell check has been carried out on failed bolts which have been found to be satisfactory. One case of connecting rod cap failure has been experienced resulting in fracture of the cap across its apex, an examination of the material showing it to have been burnt during forging process. In view of the fact that this is the only case yet experienced it is thought that the forging for this part was probably heated up twice and it was during this process that the damage was done. Reduction Gears. Following the reduction gear troubles experienced on the 420:1 ratio gear, two failures have occurred in Service on the .477 gear fitted to the Merlin III. In each case these were Crewe produced engines and suffered from similar manufacturing defects to those experienced on the lower ratio type but an examination of the failed engines showed that in each case the pinion had been running out of alignment for a considerable period prior to failure which had resulted in the rear end of the teeth being severely over-loaded and it was from this point that failure occurred. Supercharger and Drive. Following moderate speed drive failures early in the year a further source of trouble occurred recently. The facts being briefly as follows:- 1. To begin with a certain number of moderate speed clutches were burnt out in Service and in parallel to this our Production Development Department has been experiencing similar trouble on Proof Engines. In two cases clutches were put up with .040" end float in the disengaged position and were burnt out. One was found to be repairable and when this was put up with the float at .050", trouble disappeared; it being thought that when the engine was running in full speed the moderate clutch tended to drag with the result that it heated up and when for some reason moderate speed was engaged an extra load caused the already heated up clutch to slip and burn out, this figure is now universally employed on production. Since this, however, JM{Mr Morley}/Gnr. has been checking certain developments in this direction and has produced clutch failure by "feeling" for the neutral position when changing from moderate to full speed and then returning to moderate speed. This has the effect of allowing the moderate speed clutch to stop and then the re-engagement throws full torque on the clutch which causes slipping and consequent burning out. It has been suggested that incorrect setting - continued - | ||