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).
Investigation into engine running issues, including valve clearances, Autovac irregularities, and carburetter blow-back.
| Identifier | Morton\M2.6\ img044 | |
| Date | 22th September 1925 guessed | |
| -5- (c) There was difficulty in maintaining constant clearances at the valve rockers and this may have some bearing on the matter. In any case, the cause for this variation in the valve clearances, measured at different times under similar conditions, i.e. always immediately at the end of a long run, should be investigated, as unless these do remain constant as adjusted, satisfactory slow running and quietness is unobtainable. (d) It is thought, however, that the main cause for the irregularities of carburation are in the Autovac, which was not working satisfactorily. Although it did not actually fail to provide petrol at any time, the time taken to fill the chamber was very irregular. The exhaust from it seemed very feeble, as if the valves were not closing tightly, thus making the action very sluggish. Towards the very end of the run it was discovered that there was a slight leak in the pipe leading to the windscreen wiper, so the rubber tube was removed, and the hole plugged, which made some slight improvement, but did not altogether effect a cure. It should be insisted upon, whenever a Vacuum operated windscreen wiper is fitted, that a well-made cock be fitted to the connection on the inlet manifold, so that in case of any trouble, with the wiper or the long indiarubber tube leading to it, which is much exposed and very liable to perish, the connection can be readily and absolutely shut off. Two or three times on practically every day's run, whilst at full throttle and running at maximum speed, there would be a violent 'blow-back' from the carburetter, as if the petrol supply were suddenly arrested. This seldom happened more than once in each two or three hours and some days did not occur at all. Both jets were removed and found to be perfectly clean, and at no time was there found other than slight traces of sand in the main tank or the Autovac tank. | ||