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).
Letter discussing the choice between white metal and aluminium main bearings for Chassis B.135.BL.
| Identifier | ExFiles\Box 146\5\ scan0075 | |
| Date | 1st December 1938 | |
| 1245 Sr. c. Rm.{William Robotham - Chief Engineer} c. Hd.{Mr Hayward/Mr Huddy} BY.2/G/1.12.38. CHASSIS B.135.BL. MR. BOEGNER. Sr/VA.8/HB.{C. E. Harcombe}29.11.38. We wish to confirm our telegram of today, reading as follows :- "SLEATOR. CHASSIS B.135.BL. PREFER MAINTAIN WHITE METAL MAINS. CONSIDER 80,000 KILOS REASONABLE MILEAGE FOR FITTING NEW BEARINGS AND CHARGE. BY.{R.W. Bailey - Chief Engineer} & Rm.{William Robotham - Chief Engineer} ROYCAR." The reason for the decision in question is that a hard driver of this type would run into trouble with the aluminium type bearing owing to the fact that he would wear his crankshaft at a very much increased rate. If a customer achieves a mileage of 80,000 kms. then he has no real grumble that at the end of that time bearings require remetalling. You will appreciate that there is an entirely different set of conditions between fitting aluminium type bearings to the connecting rods where the lubrication is of an ideal type and the oil filtered by the position of the hole in the crankpin and fitting aluminium main bearings. We have had the same experience when we fitted lead bronze main bearings to aero engines. The hardened cranks at 650 brinell wore more with lead bronze than a standard nickel chrome shaft at a brinell of 321 running in white metal bearings, the difference being that we could run 1500 hours with a 321 brinell nickel chrome shaft in white metal bearings before regrinding, whereas with a 650 brinell shaft made in V.C.M. in lead bronze bearings, the crankshaft often required regrinding at the end of 500 hours service. In the case of the 4 1/4 we had no option but to use aluminium bearings, owing to the fact that white metal proved unreliable under the new conditions, but on the experimental Bentleys we have in hand we have reverted to main bearings in white metal, having increased the journal areas to make this possible, this being so it is obviously wrong to introduce aluminium main bearings on the 3 1/2 litre, the facts do not justify it. BY.{R.W. Bailey - Chief Engineer} | ||