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).
The development, modifications, and improved performance of the new Big Bore Bentley engine unit.
| Identifier | ExFiles\Box 90\5\ scan0085 | |
| Date | 21th September 1935 | |
| 4264 To SG.{Arthur F. Sidgreaves - MD} & Wor.{Arthur Wormald - General Works Manager} c.c. to E.{Mr Elliott - Chief Engineer} c.c. to Hy.{Tom Haldenby - Plant Engineer} c.c. to MX.{John H Maddocks - Chief Proving Officer} Big Bore Bentley Unit. We now have a big bore Bentley unit ready to go to France. During development of this unit it has been found necessary to spread the cylinder centres. This has meant a new crankcase, cylinder block, and cylinder head. It has also been found necessary to strengthen up the crankcase. Since we have had to alter the engine so much, we have taken full advantage of the strengthened parts to get the maximum power output. The attached curve shows the latest big bore power output compared with the standard engine at present leaving the Works. The biggest improvement is at the intermediate road speeds. Between 40 and 60 m.p.h. a 24% increase in power has been obtained. The engine we are sending to France is fitted with the new Hall's metal bearings. These are the only bearings we have so far found that will stand up to the power without having to run with excessive clearances. The final designs for the induction system for this unit are being completed, and the parts when made will either follow the car out or run on S-S-IV. We have fitted this large bore unit with a 10" Borg & Beck clutch which produces a definite improvement in engine smoothness. With the exception of the cylinder head, we hope that all the modified parts will be directly applicable to the big bore 20/25 which is following on. Hs{Lord Ernest Hives - Chair}/Rn.{Mr Robinson} | ||