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).
Cause of bearing failure on chassis 3.AZ.20, attributing it to contamination and improper fitting.
| Identifier | ExFiles\Box 146\1\ scan0246 | |
| Date | 4th May 1938 | |
| To Sr/VA. from HPS.{Horace Percy Smith - Experimental Factory Mgr} c. Rm.{William Robotham - Chief Engineer} c. DI. (crossed out) c. PHC. (crossed out) 1245. HPS.{Horace Percy Smith - Experimental Factory Mgr}2/VS.{J. Vickers}4.5.38. Re: CHASSIS 3.AZ.20 - CONTINENTAL TRIALS CAR. Referring to Sr/VA.1/ET.29.4.38., it would appear that seizure of No. 6 connecting rod after fitting Hall's metal bearings was due to (1) foreign matter in the oil passages (2) insufficient clearance. According to your report every care was taken during assembly of the rods, but it seems to us that the fundamental principles of a satisfactory fitting operation were entirely neglected. Clearances were not checked, and nothing was done to make certain that oil ways were clear of dirt particles remaining from previous bearing failures. In this particular instance clearances were reduced due to the fact that crankpins were .0005 above standard, but in any event it is never safe to make any assumptions regarding bearing clearances, especially in the case of a chassis which has done a considerable mileage. Bearings were diamond bored to suit a standard shaft of 2.248 crankpin diameter in order to eliminate as far as possible the need for adjustment of clearances on assembly, and it would obviously have been inadvisable for us to have made them suitable for a shaft outside drawing dimensions without precise information as to your requirements. It is observed that a satisfactory oil flow was obtained from all bearings, but after all this only proves the absence of major obstructions, and the fact that a subsequent examination revealed the presence of large plugs of decomposed oil and foreign matter after the car had only done a further 80 Kms. light running shows that the inside of the crankshaft was anything but clean at the time the new bearings were fitted. It should be appreciated that Hall's alloy bearings are definitely more sensitive than Whitemetal to the presence of dirt particles between the surfaces, and in our opinion lack of cleanliness played a large part in bringing about the bearing seizure. This is borne out by the fact that only one bearing failed, despite the fact that all six had exactly the same clearance, and we should always advocate a complete strip and thorough cleaning of all parts before fitting new bearings when it is known that a failure has taken place. HPS.{Horace Percy Smith - Experimental Factory Mgr} | ||