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).
Article on the development of high-duty bearings and materials for Bentley engines.
| Identifier | ExFiles\Box 115\2\ scan0441 | |
| Date | 11th April 1939 | |
| The Motor 374 April 11, 1939. Developments in High-Duty Bearings. Contd. POWER ON THE BENCH. Graphs showing the output of various Bentley engines, indicating the great increase that has been obtained since its inception. [Graph 1: Power Curve] Y-axis: B.H.P. (60 to 160) X-axis: R.P.M. (1500 to 4500) Legend: 1. 3 1/2 LITRE 3 1/4 BORE 2. 4 1/4 LITRE 3 1/2 BORE 3. 4 1/4 LITRE 3 5/8 BORE 1936 1.1 ENGINE Text on graph: THROUGHOUT THIS PERIOD, THE OVERALL LENGTH OF THE CYLINDER BLOCK AND CRANKSHAFT HAS REMAINED PRACTICALLY UNALTERED DETAIL. A sketch of the Bentley connecting rod showing how the cast A.C.9 material fits directly into the bearing cap without need for further backing. Heat transmission is thus improved and weight reduced. approximate to those which occur in the engine. For this reason I saw in the works laboratory valve guides surrounded by a box which keeps the guide at a high temperature. Material similar to the valve rocker is rocked up and down inside by a small eccentric device and the amount of lubrication can be varied. By this means quick results can be obtained without the necessity of using an entire engine for the purpose. Last, but not least, engineers are tremendously concerned with the consistency of the metals which they employ. Eliminating Error It is very difficult to make large castings, particularly in light alloys, which will be entirely free from blow holes. If these are beneath the surface they weaken the structure, and if they should come on a machined face they ruin it from the point of view of gastightness, or make it impossible to use some stud boss or other part. For many years foundries groped in a process of trial and error to eliminate these defects. As, however, no one could say for certain where the blow holes were until parts were machined, one might have cases where a most expensive series of operations had been taken only to find it necessary to scrap the part at the very last moment. All these troubles are now avoided at Derby, where they have installed a Phillips Macro X-ray machine which throws up a picture of the casting on a screen and enables any hidden defects to be seen at a glance. So powerful are the electric charges set loose by this apparatus that it has to be enclosed in a room with walls lined by barium sulphate and is viewed through a special screen cut in the wall by an operator standing in a small ante-room. In addition to its use in detecting faulty castings, it is, of course, also of value in showing whether or not certain materials are well bonded together, as in the case of bearing metal which is cast on to steel backings. In recent years certain bearing problems have become acute and it is in this field that the Derby metallurgists have secured one of their greatest triumphs. By unremitting effort and research they have discovered a new bearing metal for internal-combustion main bearings and big-ends which appears to be able to stand more extreme conditions, including high oil temperatures, than any material now known. The Need for New Materials The need for a metal to stand such extremely heavy duties is present on many types of modern power unit and became apparent at Derby during the course of developing the 4 1/4 litre Bentley engine. The first Bentley produced at Derby was a 3 1/2-litre having a cylinder bore of 82.5 mm. As shown by a power curve attached to this article, this unit developed a little over 100 h.p. and gave excellent results in the hands of many hundreds of owners. Eventually, however, a demand for more power occurred and this was met by enlarging the engine capacity to 4 1/4-litres. The decision had to be made whether it was better to enlarge the whole engine pro rata or not. Doing so would have helped reduce stressing on the bearings, but would have meant an increase in engine weight, and also either a reduction in body space, or an increase in wheelbase length and a further increase in chassis weight. For these reasons it was decided to obtain the extra swept volume with- COMPARISON. Friction of the light alloy bearing relative to lead bronze, showing the greater suitability of the former material for high speed work. [Graph 2: Friction Per Cent] Y-axis: FRICTION PER CENT (50 to 100) X-axis 1: SPEED R.P.M. (1000 to 2800) X-axis 2: LOAD LB/SQ. IN. (0 to 2000) Text on graph: FRICTION PER CENT AC9 TO LEAD BRONZE 70% CU. 28% PB. OIL D.T.D. 109 OIL TEMP. 100°C SHAFT NI.-CR.{Mr Cra???ster / Mr Chichester} BRINEL N° 302 | ||