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).
The test performance of Invar pistons for the Phantom II engine.
| Identifier | ExFiles\Box 14\1\ Scan013 | |
| Date | 13th November 1929 | |
| To R.{Sir Henry Royce} c. to Sg.{Arthur F. Sidgreaves - MD} c. to Wor.{Arthur Wormald - General Works Manager} c. to E.{Mr Elliott - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} c. to By.{R.W. Bailey - Chief Engineer} X7000. HS{Lord Ernest Hives - Chair}/ACL/H13.11.29. X.7000 X.1506 X.7040 Re: INVAR PISTONS - PHANTOM 11. We have run a set of Invar pistons Lec2729/30 for 10 hours on a Phantom 11 on the test bed. So far they have behaved very satisfactory, and we have had no signs of knocks when cold. We have run them up to full power without trouble. We have noticed with these pistons there is very little crankcase pressure and practically no fumes are emitted from the breather. These pistons have only four rings compared with five on the standard piston, and the fact that the crankcase pressure is low may be due to the piston head and rings being steadier and remaining concentric in the cylinder bore when either hot or cold. The weight of an Invar piston complete with rings and gudgeon pin is 2 lbs. 9.5 ozs., and the weight of a standard piston complete is 2 lbs. 7 ozs. We think, perhaps, some weight could be removed from the heads of the Invar pistons. The present pistons are sand cast, but the next set will be of forged alloy. The present pistons are ground to a clearance of .001, but this we think not quite enough because after running some time at full throttle we experience a slight loss of power, which may be due to tightness. We will try the next set with a little more clearance. We shall shortly have these pistons removed from the test engine for examination, and will supply a report upon their condition. So far this form of piston - as far as we can judge from the test bed - appears quite promising. HS.{Lord Ernest Hives - Chair} | ||