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 bearing wear following tests on balanced and unbalanced VCM crankshafts, with reference to load diagrams.
| Identifier | ExFiles\Box 115\2\ scan0377 | |
| Date | 10th January 1939 guessed | |
| - 3 - 50 hours fuel economy with a balanced VCM shaft. - This test had not done any apparent damage to the bearings. With the unbalanced shaft the engine has done two 100 hour 100 octane rating development tests and the bearings after running 328 hours are very satisfactory, - see photo KP.17 - some metal has broken away from No.1 main and a little from No.2 main but this has not seriously increased since the strip after the first 100 hours test. (b) Inspection of the crankshafts has shown heavy bedding on the journals near unbalanced webs and it was thought that this would correspond to the breaking up of the bearings, but it will be seen in the diagram of loads on the end main bearing that this part of the shaft carries the heaviest loads - see blueprint No.2, unbalanced shaft curve - the highest loads occur in the region of 180°, 360° and 600° which all fall on the journal at the part nearest the web, a further diagram is attached showing the application of load relative to the journal for an unbalanced shaft - blueprint 3, which shows that the load is carried more or less constantly on one part of the journal. This would be expected therefore to wear more than the rest of the shaft. The marking is not so prominent on unbalanced shafts as the effect is more uniform, while with a balanced shaft with balance weights unsymmetrically disposed the webs which are unbalanced have prominent marks near them. This heavy bedding is therefore not necessarily the cause of the break up of the end main bearings as these do not carry loads nearly so heavy as the centre and intermediates, and unbalanced shafts do not give the same trouble. In the appendix a treatment has been made of the behaviour of one throw assuming it to be a rectangular bar of uniform section with a mean moment of inertia of section in each principal plane found by experiment. The maximum slope of the shaft at the end main bearing lie between .001" and .002" per inch which gives edge loading of the bearing to a noticeable degree hence the bearing pressure cannot be calculated on a basis of the projected area of the bearing. | ||