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 performance and component wear after extensive mileage testing.
| Identifier | ExFiles\Box 97\4\ scan0173 | |
| Date | 23th November 1938 | |
| -2- RM{William Robotham - Chief Engineer}/IMH/3/R.23.11.38. The general standard of smoothness was good with no marked periods. A slight roughness on drive and over-run could be detected between 2500 and 3000 r.p.m. The engine mounting does not yet adequately overcome torque reaction periods. Development work is in progress. A piston seizure was experienced after 13,454 miles' running. This has been attributed to insufficient oil reaching the cylinder bores and the use of too light an oil for the prevailing conditions. The oil consumption was so good that in future more oil will be permitted to escape from the main bearings to the cylinders. SAE.20 oil should only be recommended under conditions where it is really necessary, such as cars used chiefly in towns, only for short journeys or in cold climates where starting becomes difficult with S.A.E. 30 oils. The exhaust valve seats in the cylinder head had cracked. This was a repetition of failures experienced on the test bed and on Wraith, for which a modification has been made but which was not available in time for this car. The inlet valve seats had sunk locally on the side towards the exhaust valves. The tappets were set at .008" clearance, the minimum permissible, and were good for quietness. The inlets did not change more than .002" throughout the mileage, but the exhaust lost from .004" to .010" over a period of 11,157 miles. It, therefore, appears that in future .012" should be used for the exhausts with this camshaft on Bentley V.{VIENNA} The situation may, however, be improved with the strengthened cylinder head. The Klingerite oil seals in the top valve spring washers were not satisfactory, they softened and worked out of place. Oil proof rubber seals of various types are to be tried. No.10 push rod jumped the top ball on several occasions at maximum speed attributed to a sticking valve. No harm was done and the push rod jumped back into place on slowing down. The end of the rod was dented by the ball. The Klingerite cylinder head gasket was satisfactory, but was damaged when dismantling at 13,454 miles. The front, centre and rear Vandervell strip main bearings stood up particularly well, and are the first white metal bearings to have remained intact after a 15,000 miles' test on a Bentley. The intermediate main bearings of the same type were beginning to crack up round the edges when examined after 13,454 miles, but were otherwise in good condition. At the end of the mileage pieces had broken away where previously cracked but no new cracks had developed during the last 4527 miles. Comparisons of the photographs I and II of these bearings and the last whitemetal bearings run in France on Bentley 6.B.IV in Jan. 1937, show the advance in reliability which has been made by various means since that date. | ||