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).
Inspection report on connecting rod big-end bearing failures, discussing driving habits and potential causes.
| Identifier | ExFiles\Box 146\1\ scan0278 | |
| Date | 8th June 1938 | |
| Sr/VAI/ET.8.6.38 - 2 - Nº1 - O.K. Nº2 Upper half - Loss of metal from flange. Metal also cracked on flange. Lower half - Metal slack on one flange. Nº3 Upper half - Large chunk of metal missing from shell and flange. Lower half - Metal slightly cracked and also slack on flange. Nº4 Upper half - Metal slack on flange. Lower half - " " " " and slight cracks in bearing. Nº5 Upper half - Slightly slack on flange. Lower half - " " " " Nº6 Upper half - Metal slack on flange. Lower half - Very large chunk of metal missing from shell and flange. Metal also slack on flange. In view of the above, we decided to fit a set of connecting rods having Hall's Metal big-ends. We have also fitted a large oil pump. After this experience, do you not think that we ought to revert to the fitting of Hall's metal big ends on 3 1/2 litre chassis which are permanently domiciled in France? Apparently the first owner never drove the car at high speeds. We believe a maximum speed of 115 K.P.H. was seldom, if ever, exceeded. The present owner has informed us that he only uses his car for long journeys such as Paris to Strasbourg, Austria and Italy. He has also informed us that he keeps up a good average speed and, when conditions permit, drives the car at 135 K.P.H. but he says that he never lets the engine exceed 4000 r.p.m. and, when on the straight, he frequently eases the accelerator pedal. The dismantled connecting rods are being sent to you for examination and we shall be glad to have your opinion as to the cause of the big ends cracking up. We think that the trouble is probably due to one or more of the following: I - Poor adhesion of whitemetal to the steel shell, due to faulty tinning or metalling. 2 - Excessive local oil temperature. 3 - Fluttering of the rods. 4 - Unsuitability of the above type of bearing for cars driven for long distances at high average speeds. | ||