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).
Investigations into the causes and solutions for engine piston knock.
| Identifier | WestWitteringFiles\C\August1919\ Scan63 | |
| Date | 29th August 1919 | |
| Contd. 5. EH4/LG29.8.19. proved that if one runs with a definate late ignition, the knocks disappear but no matter how early the ignition is, the knock is still there. We have tried with the ignition 110° advanced. If we run with more than this we get miss-fires. By fixing our exposed cylinder on to a piston which is knocking, the only way we can reproduce the knock with a well oiled piston, is to rock the top over by means of a sharp blow with a rubber buffer. We cannot produce any noise like a knock if we move the piston sharply bodily over. The result of our investigations so far shew us that the perfectly true piston, connecting rod and cylinder is the worst combination for causing knocks. We feel that a lot of the mystery in connection with piston knocks is now cleared up. We have still, however, to find a correct mechanical way to prevent them. The right lines to work on appear to be to have a long piston; it need not be a bearing surface all over. We also want to obtain a piston which will work with the minimum clearance. As regards this point, we find that the old thin type of aluminium piston, such as we were running on 49-GB during the war, will work with slightly less clearance than the present one and still be free. We shall be taking samples of various aluminium pistons to Mr. Royce when we visit him early next week so that we can discuss the matter. EH. | ||