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).
Tests and recommendations for modifying pistons with slots to eliminate engine knock.
| Identifier | WestWitteringFiles\Q\February1927-March1927\ 50 | |
| Date | 23th February 1927 guessed | |
| CERTIFICATE contd :- --2-- and the knocks more severe, on a piston which did not 'bed' uniformly and was subject to local high spots. It seems to indicate that the audible knock was resulting from some of these local spots losing the film of oil when reversed at the end of the stroke which had previously been maintained when in motion. This would account for the momentary increase in resistance experienced. Some tests were tried on a production car suffer-ing from particularly bad knocks in which the pistons - ordinary standard ones - were further slotted horizontally about half way down the skirt, as per appended print, in an endeavour to increase the local flexibility without altering the flexibility of the side as a whole. The results were very promising and effect a cure inasmuch as the knock could not be detected without listening against a rod pressed to the bottom of the cyl. and then only faintly. These slotted pistons were the identical ones which had previously given trouble. We are arranging to test this out on the pedestal pistons and thereby, should this slotting prove beneficial, experience the other advantages we anticipate this type of piston to possess. We therefore recommend that the std. pistons be slotted, in addition to the usual slots, in the manner shewn on the sketch as we think this would be a quick means of assisting production over some of the troubles with knocks which they are encountering. At the same time we will pursue our tests with pedestal pistons. Hs{Lord Ernest Hives - Chair}/A.C.Lovesey. | ||