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).
Modifications to address big end bearing failures on 4¼ Litre Bentley cars.
| Identifier | ExFiles\Box 146\3\ scan0223 | |
| Date | 11th December 1936 | |
| W/P. To Sr. from Rm.{William Robotham - Chief Engineer} 1020 Rm.{William Robotham - Chief Engineer}2/AP.11.12.36. BENTLEY BEARINGS. In view of your big end failure on 4¼ Litre Bentley, we have been considering the best steps to take to deal with the 30 cars of this type you have in France, with a view to ensuring as far as possible that the trouble will not recur. In dealing with these 30 cars, some consideration has to be given to the cost of the modification. My recommendations to the Administration are as follows - There is no object in removing the crankshaft from the crankcase, because at present we do not know of a better bearing material to be put in the main bearings. We think the standard Whitemetal will last just as long as the Hall's alloy; the tests on your Trials Car will give us more information. We therefore recommend that when these cars are available, the main bearings should be dealt with in the same manner as previously i.e. taken up by stepping the shims. The big end bearings should be replaced by R.R.56. material and fitted with RR.56. shims. We are changing over to this material on Production and it is only a question of the time taken to get the material before it will be fitted to all Bentley cars. We also recommend that in every case you should replace the existing oil pump with a large oil pump. We think after this changeover, the chances of failures of big ends are somewhat remote, particularly in view of the fact that our experience shows that when once main bearings have been taken up they do not hammer out further. On new cars leaving the factory, we are introducing wider grooves in the intermediate bearings, two oil holes in the crankshaft, large oil pump, RR.56. big ends and shims and the Phantom III. type of filter. The filter is introduced because at the present it is the only way we know of helping the main bearings. We do know that on the test bed, where we have elaborate filtering arrangements, we can run what is equivalent to 50,000 miles on the road, and the crankshaft is only scored to a negligible extent. For future cars, we are immediately increasing the size of the crankshaft which will give us 36% increase in area on the intermediate bearings and 50% on the centre and main bearings. 6.B.4. leaves for France immediately after Christmas with improved Whitemetal mains and RR.56 big ends. continued | ||