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).
Technical discussion on overcoming piston knocks and seizing issues with a new split piston design and the use of oil.
| Identifier | ExFiles\Box 48\1\ Scan109 | |
| Date | 30th September 1919 | |
| Contd. -3- to overcome piston knocks we shall get into seized piston trouble. A number of the pistons do seize up but a still greater number run tight and have to be eased. The pistons which are seizing up have a clearance of .009" to .006" With this split piston we can run full power with a clearance of .005" to .004". There is no signs of it seizing up, in fact, we think this piston, as regards not seizing should be the millennium. There is also no sign of knocks, either hot or cold. There is no need, of course, for us to make them with such tight clearances as .005" to .004". If we made them 2 thous. less than the clearances used on the present pistons, we are sure we should get no knocks when hot and very much reduced knocks when cold. We think this piston is good for the following reasons:- 1. The pressure side of the pistons is left identical as on the present pistons. 2. On an average car we think that for 70% of its running no pressure would be exerted by the piston on the cylinder walls because the car would be running at reduced throttle so that the temperature could be such that the piston would not be expanded to the maximum. Under those conditions this piston should work in the same way as the present standard. It is only in the extreme conditions of continuous full power where we anticipate the piston will collapse those few thous. to avoid seizing. 3. This piston can be made out of the present standard castings but any pistons which have been ground would have to be scrapped. 4. We consider it should be impossible for this piston under the very worst conditions, to ever seize up. Use of oil to Avoid Piston Knocks. We are making progress in this direction. We have been able to cure very bad knocks by the use of oil. We | ||