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 filter plug failures and material recommendations for Stromberg carburetters on various chassis.
| Identifier | ExFiles\Box 93\2\ scan0192 | |
| Date | 15th May 1937 guessed | |
| (2) Stromberg was fitted. The filter gauze on the 25/30 was specified to be the same as a Stromberg sample when the Stromberg carburetter was adopted on this chassis. The presence of the aluminium needle like fragments appears to be due either to a poor thread in the filter body, a plug cap for which an insufficient chamfer is specified on the leading edge of the thread, and also a place on the leading edge where the thread has been slightly damaged. Actually the plug would not screw right home when the aluminium joint washer was removed and more metal was cut off the thread in trying to make it do so. In the case of Sir John Lee's car in which the flooding occurred it is quite possible that when the car was cleaned out after the first flooding the removal and replacement of the filter plug cut off some portion more aluminium and caused the second failure. We know that the aluminium washer that makes the petrol joint requires the plug to be screwed up very hard. Taking the evidence by and large it is quite possible that the small damage on the end of the plug thread, which looks more like a small file cut rather than due to the plug being dropped may be the cause of the aluminium being removed. The trouble on the other Phantoms may also have been due to the filter plug threads being damaged, and we know by experience that this damage can easily arise from a small flat on the thread caused by the plug being dropped. Although we have plenty of steel and bronze plugs in aluminium in other places, including the carburetter, I think we should discontinue this practice in future in connection with the filter bodies, and make these parts in brass. Actually the 25/30 filter body is in the latter material for other reasons. It is difficult to see why we should use a stainless steel plug on the Phantom III and mild steel plated on the 25/30. With regard to the filter units, these consist of gauze cylinders with metal rings sweated in each end, and the bore of the metal ring makes a sufficiently good joint to form a seal. The fit of these rings however on the filters we inspected was spoilt by being scraped out to remove the solder, with the result that they were very slack. | ||