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).
Tests conducted on different crankshaft dimensions for the 25 HP engine to determine critical speeds.
| Identifier | Morton\M19\ img007 | |
| Date | 15th January 1931 | |
| To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} c. to SG.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} c. to Da.{Bernard Day - Chassis Design} E.{Mr Elliott - Chief Engineer} c. to Rg.{Mr Rowledge} By.{R.W. Bailey - Chief Engineer} ORIGINAL Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}/RT.15.1.31. X5010, CRANKSHAFT DIMENSIONS. 25 HP. It will be remembered that during a recent visit to West WitteringHenry Royce's home town the question of the optimum crankshaft dimensions was discussed. We rather felt at the time that to increase the size of the crankshaft pins above the present dimensions would give us no advantage unless they could be considerably lightened and additionally might actually be a disadvantage when balance weights were fitted. To obtain more information we have carried out tests on the two 40/50 crankshafts we have available which are identical except for the pin dimensions. One has 2.125" dia. pins and the other 2.375" dia. pins. The object of the tests was to establish the critical speed or master period of each crankshaft, and to determine the point accurately the car was towed with the rocker shaft removed so that the noise of the valves would not mask the crank period. The results obtained were as follows:- | Journal Dia. | Pin Dia. | Critical Speed or Master Period | Description of Crankshaft. Piece No. | |---|---|---|---| | | | Engine R.P.M. | Top Gear Road Speed MPH. | | | 2.625 | 2.125 | 3760 | 100. M.P.H. | Present stand. Shaft Wt.79 lbs E.79738. | | 2.625 | 2.375 | 3690 | 98.2 M.P.H. | Large Pin not yet standard-ised. Shaft Wt. 80 lbs. E79640. | | 2.625 | 2.125 | 3100 | 82.0 M.P.H. | 12 balance wts to H.W. sch. E.78548. | All crankshafts were fitted with low inertia spring drives to E.79915. An interesting point is that whilst making the test on the large pin (2.375") dia. crankshaft the centre main bearing and the bearings either side of it collapsed showing practically | ||