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).
Correspondence regarding piston cramping, slack, and slap issues, proposing an increase in the clearance hole diameter.
| Identifier | ExFiles\Box 48\1\ Scan152 | |
| Date | 3rd January 1922 guessed | |
| contd. -3- Although we have not been able to thoroughly investigate this matter as yet, we believe that this cramping of the piston on the small diameter may account for some of the collapsing of pistons when running on the engine. For example, we find that after a new engine has been run an hour or so, (to run in the timing gears) the pistons will sometimes show .006" slack in the cylinder. We therefore consider that the clearance holes in the piston bosses shouldbe increased from .266" diameter to .312 diameter so as to avoid any possibility of cramping the pistons. As an example of the troubles which arise with the present type of piston, we may mention that on 22-LW (our first English demonstration car) we have had to peen out the pistons four times in 9000 miles of running, each time to prevent knocking which had developed. This is not elusive knocking but sheer piston slap. We should like the opinion of Mr. Royce and the works Committee on this suggestions, and their comments on the piston design of the Aluminium Manufacturers, Inc. Yours truly, ROLLS ROYCE OF AMERICA Inc. per. M.Olley. MO/G.{Mr Griffiths - Chief Accountant / Mr Gnapp} | ||