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).
Comparison of pedestal pistons versus standard pattern pistons, detailing their characteristics and performance.
| Identifier | ExFiles\Box 48\1\ Scan176 | |
| Date | 4th April 1926 guessed | |
| còntd :- -2- knocks it seems to possess very similar characteristics to the standard pattern. It has been previously pointed out that the knock experienced is of a different nature to that obtained with a slack piston and furthermore we have demonstrated that when a standard piston having standard clearance is inserted in a steam heated cylinder, the piston expansion completely takes up all the clearance and becomes tight. We believe the pedestal piston to possess certain advantages over the standard piston pattern - the outstanding ones being :- (1) A more satisfactory method of fixing the gudgeon pin and reducing the tendency to distort the piston. (2) For the same clearance when cold better freedom is obtained when hot due to the greater flexibility. The latter seems quite important. So far we have not experienced tightening up in the engine even when the piston has been as much as .004 oversize when cold. With the standard piston it has always been necessary to work to close limits in order to prevent undue tightness when hot under full load conditions. MADE AT CROXLEY During a recent test with these pistons ground to have dimensions ranging from standard up to .004 oversize, it was found, after a few minutes light running to warm up, possible to run up to full load and speed without any symptoms of tightness, whereas with the standard type it was always found advisable to devote a period to 'running in' before attaining full load. In view of these facts it is reasonable to suppose that contd :- | ||