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 development and testing of Borg & Beck clutches, including balancing methods and spring performance.
| Identifier | ExFiles\Box 129\3\ scan0023 | |
| Date | 6th January 1936 | |
| -2- We have discussed the matter with Borg & Beck and we find that their method of balancing is to balance the pressure plate alone, then to assemble and balance the complete clutch by drilling further holes in the pressure plate. This of course throws the pressure plate out of balance again. They are going to let us know how much out of balance there is in the plate in case E.{Mr Elliott - Chief Engineer} Meanwhile, acting on the above theory, we are returning to them the production clutches which have already been delivered, for them to re-balance the pressure plates and then balance the clutches by drilling holes in the cover, not in the pressure plates. We have examined the clutch taken from B-56-BN{W.O. Bentley / Mr Barrington}, which has done 15,000 miles in France, and find it to be in excellent condition. The maximum wear in the cover plate slots is .006". Clutch Springs. When we first commenced development work on the Borg & Beck clutch the torque to be catered for was 176 lbs.ft., i.e., the engine was to have been the old 3½ litre Bentley. As we were anxious to keep the flywheel inertia down we chose the 10" size as being the most suitable for our job, and Borg & Beck agreed to this, but stated they had no experience of the 10" clutch when used for bigger torques than this. The total spring poundage was 1320 lbs., and taking the nett torque of the 3½ litre engine to be 178 lbs. ft., the working 'µ' is .20. When we came on to the large bore engine, we retained the same springs, and despite the fact that the working 'µ' was now .23, no slipping trouble has occurred. These springs were used on the 15,000 miles test on B-56-BN{W.O. Bentley / Mr Barrington}, and the clutch has been successfully tested with large bore engines in London and Paris traffic and on Porlock Hill. We appreciate that .23 is a higher 'µ' than we have ever used before, but we think that the higher the power/weight ratio of a car, the higher the permissible working coefficient of friction. This was demonstrated to us on Porlock Hill, where we made comparative tests between 10" Borg & Beck clutch fitted to 3½ and 4¼ litre engines. It was found that the take up was, if anything, better on the larger car, owing to the fact that sufficient starting torque could be obtained with lower engine speed. | ||