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).
Crankshaft design improvements for the Bentley 3.5' bore engine.
| Identifier | ExFiles\Box 85\5\ scan0096 | |
| Date | 29th June 1935 | |
| To E.{Mr Elliott - Chief Engineer} c. to Wor.{Arthur Wormald - General Works Manager} c. to Da.{Bernard Day - Chassis Design} c. to By.{R.W. Bailey - Chief Engineer} c. to Hdy.{William Hardy} 4217 Bentley Crankshafts. When re-designing the Bentley engine for 3.5" bore we think it would be a good opportunity to incorporate various crankshaft improvements. We attach herewith a sketch of the existing standard crankshaft, the experimental narrow pin shaft, and the shaft we suggest for the new engine. The pins for the latter are 1.125" long, the journals 2.500" dia., and make use as a bearing of all the available length from shortening the pins instead of having shoulders on either side of the journal as in the first narrow pin crank. For the rear bearing we suggest the large 4-stud arrangement already designed. The journal diameter is increased as the life of the present ones is less than the big ends. Increasing their length will reduce the oil leakage. We are still of the opinion that the large change in section at the front end from the journal to the crankshaft nose is detrimental as regards the speed of the master period and the amplitude of lateral vibration of the slipper wheel centre which accompanies a torsional vibration. We know this lateral vibration exists from experiments on Peregrine engines. The only way we have found for prevention of slipper wheel centre failures on 10,000 miles tests is to limit the float of the crank pinion. E.{Mr Elliott - Chief Engineer} has pointed out that this would not be easy in production quantities. A short time ago we asked for a design of slipper wheel having 50% increased inertia, a strengthened centre and cork inserted friction discs. We recommend this is incorporated in the new engine and that advantage is taken at the same time to increase the diameter of the crankshaft nose. | ||