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).
Recurring big end bearing failure during a 15,000-mile test of car B-56-BN.
| Identifier | ExFiles\Box 83\4\ scan0216 | |
| Date | 19th May 1936 | |
| X264a To Sg{Arthur F. Sidgreaves - MD}, from Rm.{William Robotham - Chief Engineer} c.c. to Wor.{Arthur Wormald - General Works Manager} c.c. to L. c.c. to Ry. 15,000 miles Test - B-56-BN.{W.O. Bentley / Mr Barrington} We have had a telegram from Chateauroux to say that another big end bearing has failed. It will be remembered that at 12,000 miles a big end failure occurred. After this a complete new set of connecting rod bearings were fitted, and the present failure has taken place after 4,000 miles. The two bearings which have failed are numbers 2 & 5. In considering these failures it should be remembered that we have run more than 500 hours on the test bed under full throttle maximum power output conditions, without experiencing this trouble. We believe that the failures on the road are due to insufficient oil supply to the crankshaft pins. The oil supply is insufficient on this car because of the wear which has taken place on its main bearings. The wear on the main bearings as far as we can ascertain is accelerated by the fact that the filtering arrangements on the 20/25 and Bentley are not sufficiently good for a hard bearing material. The white metal bearings which have been used up to the present are soft and do not tear up when small particles of foreign matter pass into them via the lubricating oil. Apparently on this car at 11,000 miles the connecting rods were beginning to be short of oil and so a failure took place, and this has just been repeated. In considering this failure it should be remembered that every 3 1/2 litre Bentley which has so far been sold to the public would have destroyed its connecting rod bearings at about the same mileage, and therefore there is no undue cause for alarm because customers do not drive their cars as we do at Chateauroux. Nevertheless we are satisfied that we can vastly improve the bearing life now that we have seen what happens on the road, and are co-operating with the Design Dept. to get out a specification for a unit to run the next 15,000 miles test. | ||