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).
Analysis of connecting rod cap failures on a Bentley unit, considering torsional vibration as a potential cause.
| Identifier | ExFiles\Box 85\3\ scan0083 | |
| Date | 12th April 1934 guessed | |
| -2- pressure was 19 lbs/sq.in. under the same conditions, and a very much larger proportion of the oil circulation went through the bearings. There has been one other failure on a Bentley unit (C.XI) with the Dural Con. Rods. This occurred with rods of the original design - i.e., weaker caps - on No. 4 cylinder after 26 hours F.T. running at and above 4000 r.p.m. In this case it was by no means certain that the failure was due to the rod, as it may have been due to the piston. In the case of the present failure, it is perhaps significant that No. 1 should fail first and that No. 2 should be cracked while all others were satisfactory. This suggests that torsional vibration of the crankshaft is playing a part in breaking the caps. This may easily be so in the present case as the unit used for the tests had a master crankshaft period at only just over 4500 r.p.m. The rods had run for 24 hrs. at 4500 r.p.m., 1 hour of which was continuous. It is not suggested that the rods would not fail if running out of the range of the period, but that they would last longer. The attached photograph No. 2 shows suggested alternative methods of strengthening the Con.Rod caps. Hs{Lord Ernest Hives - Chair}/F.J. Hardy. | ||