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).
Engine component wear and potential design improvements for main bearings and connecting rods following a 15,000-mile test.
| Identifier | ExFiles\Box 97\4\ scan0251 | |
| Date | 7th December 1938 | |
| -2- MAIN BEARINGS - Cont'd.{John DeLooze - Company Secretary} Regarding their condition after the 15,000 miles test, the front, centre and rear bearings are excellent and show only a maximum wear of .001. The intermediates are beginning to crack away at the edges, otherwise are in good condition with a maximum wear of .0005. The makers have several alternatives including a new form of bearing metal to correct the intermediate bearing cracking trouble. Experimentally we are going to try a 2.75 main journal as against the present 2.5. Loose thrust washers are used to locate the crank end float and these can be regarded as being in the same category as the intermediates, i.e. hardly up to the job, also the grooves in the thrust faces allow more oil than standard to leak across the faces, which creates a slight leak into the clutch pit. To overcome this we are experimenting with a longer oil retaining thread on the crank, which in the case of the standard engine will be an additional safety factor against leaks into the clutch pit. Summarising, we would say that for the cheap engine with the improvements mentioned, the Vandervell bearings could be introduced with the .4 carbon crank. CONNECTING RODS (FORGED TO SIZE). Despite the fact that the rods as run on this unit were condemned before running some time ago, they have completed the 20 hours endurance and run the 15,000 miles and are free from cracks. The dies for this rod do not permit the use of the present thin section big end bearings, therefore it is necessary to sink new dies to produce rods, which other than not being machined except at the big and little ends are up-to-date. Drawings for these rods have been done to LOP. EB.4295 and in view of the satisfactory run of the forged to size rods which effect an approximate factory cost saving of 42/- per engine, we consider that the necessary new dies be sunk and further sets be tested. | ||