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).
Continued analysis of clutch slipping and overheating, with a comparative table of different clutch specifications.
| Identifier | ExFiles\Box 179b\3\ img023 | |
| Date | 7th January 1933 | |
| -2- He/Aln.1/MA.7.1.33. Cont'd.{John DeLooze - Company Secretary} The quantities found do not definitely explain the slipping experienced but it is clear that the design allows very little margin, particularly if there are cyclic variations in the engine torque. There has certainly been overheating as discoloration shows on the rear (moving) clutch ring. The marks occur, curiously, at the four points on the face, behind which the withdrawing lugs are cast, suggesting that the ring distorts when hot, though it is flat when cold. The four pads on the operating levers and the adjustable pads in the plate on which they bear all have fairly deep pit marks. As these are only under pressure when the clutch is withdrawn and have extremely little sliding action this suggests that the cause of the trouble may be that the withdrawing mechanism has been adjusted rather tightly, thus accounting for both the pitted lever pads and the slipping of the clutch. Below is a table giving leading particulars of the clutch together with those applying to the standard Peregrine III. For comparison a column is added for the Borg & Beck clutch supplied by the makers to suit our 20/25 engine. It will be seen that the standard Peregrine has a much better margin than the N.sch.3513 clutch but also that it has a very high fabric loading. The Borg & Beck clutches seldom exceed 30 lbs.per.sq.in. loading for private cars or 20 lbs. per.sq.in. for buses. The friction coefficient of .23 was found with their special material. COMPARISON OF CLUTCHES. Peregrine Standard Borg & Beck B & B type Peregrine 1C.A-1-G.{Mr Griffiths - Chief Accountant / Mr Gnapp} N.sch.3513 G.100500 Fabric outer dia. 9.0" 9.0" 9.85" " inner " 6.25" 6.96 6.10" " effective mean radius, 3.85" 4.0" 4.07" Spring free length 2.00" 2.44" 2.575" " assembled " 1.315" 1.80" 1.60" " rating (lbs/in) 160.3 265 179 " assembled press. (lbs.) 110.0 169.7 155.0 No. of springs 8 to G.101054 6 to GKO787 9 Spring total press. (lbs) 880.0 1018 1395 Coeff.of friction µ .21 .21 .23 Max. torque (lbs.ins) 1422 1710 2610 | ||