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).
25 HP engine clutch slipping issues, comparing spring loads with the 40/50 model and detailing proposed modifications.
| Identifier | ExFiles\Box 179\2\ img117 | |
| Date | 5th January 1932 | |
| ORIGINAL To E.{Mr Elliott - Chief Engineer} From Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} c. to By.{R.W. Bailey - Chief Engineer} Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}1/MJ.5.1.32. X8480 25 HP. CLUTCH. With the increased size of the 25 HP. engine the clutch has always been on the point of slipping. The original loading of the 25 HP. clutch spring was 105 lbs. This was raised to 125 lbs. when the bore was increased to 3. 1/4 ins., but it was still found that the margin of safety was not enough. Some of the tests were rather complicated by the fact that the automatic clutch lubrication allowed oil to get on the clutch fabric which caused slipping, but we have now more or less established that the clutch spring load of 143 lbs. is about the minimum required for satisfactory operation. Unfortunately, with these springs and the existing 25 HP. clutch leverage, the pedal pressure is impossibly heavy - being 64 lbs. with the pedal fully depressed, against about 45 lbs. for the 40/50. We have therefore altered the clutch leverage as per the attached sketch, at the same time stiffened up the clutch fingers and torsion shaft, to reduce the lost movement by deflection. By comparison with the 40/50 it may be considered the spring pressure we are asking for the 25 HP. is too high but we have made careful measurements of the 40/50 springs with the following results :- Actual free length in service 3.990. Actual rating 162 lbs/in. Actual loading when the clutch is home 234 lbs. Therefore total clutch spring pressure 1872 lbs. Now allowing for the difference in mean clutch radius, the 25 HP. spring pressure should be .7 that of the 40/50 which means a loading of 165 lbs/spring to be in the same proportion. We therefore do not consider the 143 lbs. springs called for are too heavy. We have tested out the modifications proposed on 19-G4, with satisfactory results, and they will be running the next 10,000 miles test on 18-G4. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} | ||