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).
Letter to F. J. Hardy discussing gear stress, capacity, and recommendations for suitable steering gear sizes.
| Identifier | ExFiles\Box 153\4\ scan0100 | |
| Date | 11th June 1941 guessed | |
| Contd: -2- F.{Mr Friese} J.{Mr Johnson W.M.} Hardy, Esq., type as that showing on the Cams you send us, but the last of these instances was some years ago now. We never got down to the bottom of it at any time for certain but eventually came to the opinion that it was probably started by foreign matter, possibly of quite small size, getting between the pressure faces of Cam and Roller. This would produce a very heavy local stress which could start things happening to the case. Coming now to the capacity of the Gear and the duty you have put it to do, it would appear that the Rockershaft pitch radius (Rockershaft centre line to Cam Track pitch line) is something under 1½" - the actual Gear ratio somewhere in the neighbourhood of 16 to 1. Assuming the above and the car weights and tyre sizes you give in your letter, from our data, you are certainly stressing the Gear up to its maximum. Seeing the Car is a pretty speedy one, my opinion is that for long life and a margin for safety a larger Gear is highly desirable. For size the Gear would seem to be approximately in line with our '461' Gear shown on the enclosed Drawing GA.3706. For a Car of the capacity, weight and performance we imagine it to be, we would certainly recommend our '561' size as shown on Drawing GA.3702, also enclosed. For your information, we rate our '461' Gear at 3600 inch lbs. full load capacity maximum and our '561' at 5000 inch lbs., the pitch radii of the '461' Gear being 1.427" and 1.706" for the '561' Gear. Both the Cam Tracks and the Roller Track show signs of high pressure, as do the cam end bearing races. I have, therefore, come to the opinion that these parts have been subjected to a duty which leave little or no margin for eventualities which sooner or later are experienced, particularly in Steering Gears, though I put this opinion forward with reserve as I do not feel the amount of evidence I have to go on is very large. P.T.O. | ||