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).
Test bed results for Phantom II Invar pistons, detailing issues with clearances and cold knocks.
| Identifier | ExFiles\Box 15\3\ Scan042 | |
| Date | 15th January 1930 | |
| To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/ACL. C. to H.E. WRT. C. to M.R. DM.{D. Munro} C. to BP. X7040 PHANTOM II INVAR PISTONS. We have continued our tests on the test bed with Invar pistons. It will be remembered from a previous report that with the circular ground pistons we had trouble with the pistons tightening at the ends of the alum. pads when fitted with clearances which gave freedom from cold knocks. It was further found that if we went as far as .003 clearance we were troubled with cold knocks but free from this trouble when the engine was hot. We next tried some eccentrically ground pistons having .001 clearance across the centres of the pads and .003 across the ends of the pads. These pistons when first run were excellent from the point of view of freedom from cold knocks and only required a short period of 'running in'. After a total of about five hours running, two of the pistons showed slight signs of knocks. When taken down for examination these pistons showed excellent bedding over the pads. Our experience with these pistons has been that it is an exceptionally close job - a matter of half thousandths- to provide pistons which are free from cold knocks and be free from tightening up at full throttle. Their characteristics appear to be very similar to the cast iron pistons i.e. we are dependent upon very fine limits for good results. It is our experience that for consistent | ||