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).
Potential causes for trouble with aluminium pistons on the 49-GB car engine, such as carbon deposits or expansion.
| Identifier | ExFiles\Box 35\2\ scan 193 | |
| Date | 15th January 1920 | |
| X.2748 To Hs.{Lord Ernest Hives - Chair} from R.{Sir Henry Royce} Copy to CJ. " " Bn.{W.O. Bentley / Mr Barrington} " " Da.{Bernard Day - Chassis Design} " " PD. " " CK.{Mr Clark} X.2748. - RE ALUMINIUM PISTONS. Hsl/LG15.1.20. R9/G20.1.20. X.2631. X.682. X.3715. With reference to the pistons on 49-GB, there seems little doubt that the trouble with these pistons, as you point out, is in some way due to the deposit of carbon. To me it is a mystery why a similar fault has not occurred in the aero engines, and it is just possible that the car engine cylinder does not remain circular in the same way as the engines with over-head valves. At first sight it would appear that the trouble is due to the low down position of the piston rings, but as far as I remember of 7-CA, which had the same fault, in this case the pistons rings were not low down, and were not of the narrow type. If it is due to the extra expansion of the aluminium pistons, one would expect that it would occur also to some extent, with cast iron ones. It would certainly be interesting to find out if the turning down of the upper part of the piston really cures the fault, and I think it would be worth while taking another similar trip with 49-GB fitted with oil plunger pistons, so as to get comparative figures, unless you can see your way to do so under ordinary circumstances, or some further information is forthcoming. Contd. | ||