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 assessment of various clutch options from Borg & Beck, detailing their torque and speed limitations.
| Identifier | ExFiles\Box 130\3\ scan0138 | |
| Date | 2nd December 1940 | |
| Rv/GB.6/ST.2.12.40 - 2 - Starts on full engine torque should be infrequent, in view of the ample size of the engine. The quantity of liner which can be worn away is not increased by using two discs instead of one, as it is controlled by the available clutch adjustment. The coefficient of friction for Ferodo R.A.D.11 is about .35. It was stated that .30 could be used for design purposes. Ferodo would like one of their standard sizes of disc to be used, as new dies are difficult to obtain. A liner temperature in excess of 550-600° F.{Mr Friese} is not recommended. BORG & BECK. Messrs. Shinkins, Barker & Godfrey represented Borg & Beck, and their comments and recommendations are given below. When reading these, their statement that they tend to be "slightly conservative" should not be forgotten. 14" twin disc clutch - Not recommended for torques above 610 lb.ft. Is right out of the question for 1200 lb.ft., however light the vehicle. 16" twin disc clutch - This size is not recommended for torques above 1050 lb.ft. but might be made to take 1200 lb.ft. They have no design for this size of clutch and could not supply a clutch of this size in less than 3 months. 18" twin disc clutch - This size is capable of transmitting a torque of 1200 lb.ft., but it was suggested that the maximum speed should not exceed 1500 r.p.m. when made in C.I. If the clutch were made in "Nitensile" it might be permissible to reach 2000 r.p.m. However this is the clutch that Borg & Beck would like us to use. In a letter received since the visit, it is stated that 2000 r.p.m. is a safe speed. It is not clear whether this applies to a C.I or a Nitensile clutch. 18" single disc clutch - This is to be supplied to Vauxhall for use in A.22 tanks. The maximum engine torque is 840 lb.ft. and the maximum speed 2400 r.p.m. This clutch could not be recommended for our torque. Of the above clutches, only one can be recommended for a torque of 1200 lb.ft. and this clutch is not recommended for use at speeds above 2000 r.p.m. | ||