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).
Static deflection tests for a new method of positioning crankshaft balance weights on a Bentley crankshaft.
| Identifier | ExFiles\Box 85\5\ scan0111 | |
| Date | 20th May 1936 | |
| Copy Ha/Gry.{Shadwell Grylls}18/RW.20.5.36. A new method of positioning Crankshaft Balance Weights. While in Detroit, Packard's told us in connection with crankshaft balance that the orthodox method of calculating balance weights to give mass balance was incorrect and extravagant in added inertia, and that in practice four weights correctly positioned would counteract the deflections caused by the centrifugal loading for 6 throw crankshafts. We therefore carried out the two following static deflection tests on a production Bentley crankshaft. (1) Supported on knife edges on the end journals measurements were taken of the deflection downwards of each journal with 100 lbs. (a) Downwards on crankpins 3 & 4 the throws also being downwards. (b) Similarly on pins 2 & 5, these throws being downwards. (c) On pins 1 & 6. By superimposition of the deflections obtained we could see the shape of the crankshaft when running unbalanced. This shape consists of a bow in one plane only at 40° to the direction of throws 3 & 4. (2) Not believing this result and doubting the effect of the weight of the crankshaft itself we supported the crank vertically on a ball at each end and applied 100 lbs. load to all 6 pins simultaneously. The deflection was identical with exp. (1). A single load of 71 lbs. at the centre journal returned the crank to its original unloaded shape exactly in the middle and to within .001" at the other journals. | ||