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 running of Phantom II Invar pistons, detailing issues with clearances, piston knock and recommendations for eccentric grinding.
| Identifier | WestWitteringFiles\T\2July1929-December1929\ Scan227 | |
| Date | 27th December 1929 | |
| To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/ACL. C. to SG.{Arthur F. Sidgreaves - MD} WOT. C. to E.{Mr Elliott - Chief Engineer} Da.{Bernard Day - Chassis Design} C. to By.{R.W. Bailey - Chief Engineer} ORIGINAL HS{Lord Ernest Hives - Chair}/ACL.1/WAJ.27.12.29. X7040. INVAR PISTONS - PHANTOM II. We have done altogether about twelve hours test bed running with various sets of Invar pistons and tested various clearances. We found the engine would not operate satisfactory with less than .00175 to .00200 piston clearance - in fact this appeared a little close for full power running and it was necessary to give the engine a considerable amount of 'running in' before any full load tests could be taken due to piston tightening. With the above clearance there is no sign of piston knocks when the engine is cold. One set of pistons we tested with .003 clearance but when this we ran into bad cold knocks although these disappeared when the engine was at normal running temperature. Cold piston knocks with .003 clearance are definately too bad to permit the use of such clearance. Inspection of these pistons after running shews that the 'bedding' at the sides of the Alum. pads is much heavier than at the centre. So far all pistons have been concentric ground. Results would indicate that eccentric grinding would be more suitable for this type piston. We are consequently grinding a set of pistons having only .0015 clearance at | ||