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).
Experiments to investigate and reduce engine knock using rubber washers, different piston types, and extra oiling.
| Identifier | WestWitteringFiles\O\2April1926-June1926\ Scan004 | |
| Date | 1st April 1926 guessed | |
| contd :- -4- cut in the crankcase to permit this - the noise appears practically the same for each cylinder. Experiment 1. To explore the influence of the crankcase on the knock a thick rubber washer was placed between the cyl. blocks and the crankcase. This resulted in the knock being more pronounced and seemed to be of about equal intensity from each cyl. block. This experiment rather indicates that the crankcase exerts a damping influence on any sound set up in the cylinder block and that the front portion is more efficient in this respect than the rear. It will be remembered that the front part of the crankcase carries the dynamo, and is of stiffer section, although we have tried to reduce the knock by stiffening the rear part with tie bars passing across the upper half, but without success. Experiment 2. Cast iron pistons - without the skirts being split - were tried but found to possess the same characteristics as the aluminium pistons. These were ground to have the same clearances as the cast iron pistons which were used on the old Silver Ghost i.e., a clearance of .0008 to .001". Experiment 3. Oil under pressure was admitted to the cyl. bores on the pressure side similar to the arrangement of 'extra oiling' on the Silver Ghost engine. A tap was provided so that the oil could be turned off or on during the experiment. This considerably reduced the knock and it could be detected and then only slightly, by employing a listening rod at the cyl. base. contd :- | ||