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 and clearances for Invar pistons in a Phantom II engine.
| Identifier | ExFiles\Box 15\3\ Scan039 | |
| Date | 27th December 1929 | |
| To. R.P. From HS{Lord Ernest Hives - Chair}/ACL. c. to SS.{S. Smith} c. to H.{Arthur M. Hanbury - Head Complaints} Ds. c. to By.{R.W. Bailey - Chief Engineer} X7040 Hs{Lord Ernest Hives - Chair}/ACL.1/MJ.27.12.29. 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 with 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 | ||