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).
Report discussing the causes of extraordinary engine main bearing wear on chassis B.125-GP.
| Identifier | ExFiles\Box 146\1\ scan0272 | |
| Date | 4th June 1938 | |
| 1245 BY.10/C.4.6.38. C. Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} CHASSIS B.125-GP. MR. J.{Mr Johnson W.M.} FAURE. Levallois - Sr/VAll/ET.30.5.38. Referring to the extraordinary wear which took place on the above engine main bearings after completely refitting the bearings at 13,400 miles, the only suggestion I can make, which I think would have a bearing on the case is as you suggest in connection with ovality. The point I have in mind is that in re-fitting a crank with a certain amount of ovality on the journals it is essential that the minimum working clearance should be permitted over the maximum diameter of the journal i.e. there should be .00275 clearance over the maximum diameter of the journal. Where ovality occurs, in this case originally .0015, the working clearance would be increased over these areas by the amount of the ovality, but under these circumstances the crank would float on the oil film satisfactorily. I am rather inclined to think that the cause of the trouble is that the normal working clearance was allowed over the worn surface of the journal. This would leave insufficient clearance over the maximum diameter of the journal, the result would be heating up of the bearing metal which under such circumstances would certainly tear up and seize badly on the shaft. In regard to the fact that there was a bow of .012" on the crankshaft, we are satisfied that this has no bearing on the subject, as we have run plenty of cranks with as much as .015 bow without the slightest disability, both on the test bed and in chassis. Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} has written a separate memo on the subject, asking for the return of the bearings if these are available. We are interested in seeing whether the material of the bearings was within the specification, personally I should expect to find them so owing to the care which is taken, but we would like to make certain of this point. As the worn bearings were Nos. 1, 2, 3 and 4 it rather indicates that the owner may have been running on 3rd gear on the fringe of the master period of the crankshaft. It is difficult, however, to prove such a point, although the loose big end bearings rather point to a similar condition. | ||