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).
Standards for piston knocks and the challenges with piston clearances on different vehicle models.
| Identifier | ExFiles\Box 35\2\ scan 098 | |
| Date | 22th August 1919 | |
| To R.{Sir Henry Royce} from EH. c. to CJ. c. to BN.{W.O. Bentley / Mr Barrington} c. to E.{Mr Elliott - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} c. to Wor.{Arthur Wormald - General Works Manager} EH2/LG22.8.19. 22nd. Aug. 1919. X. 2748. RE PISTON KNOCKS. X.2748. X. 2565. We realised when we let you have 1.E.X. that it was a very bad example for piston knocks. 1.E.X. will not pass the standard which has been laid down, that is, there shall be no knocks when the water is at 50°C. The piston clearances on 1.E.X. are slightly in excess to what we are fitting as standard. The average production chassis will be about similar for piston knocks as 7-CA. but to obtain that degree of silence at present. it will mean scrapping a certain percentage of pistons. This is no more than we had to do with the cast-iron pistons. Will you be satisfied if no cars are delivered which are any worse than 7-CA?. If the Sales Dept: and Mr. Johnson Expect cars to be entirely free from piston knocks even when cold, they are setting us a tremendous task. Before the war we know that cast iron pistons were fitted with only .002" clearance in the endeavour to overcome piston knocks. We arrived at that as the only means to overcome piston knocks aftery years of experience with the trouble. No one desired to run with such fine clearances because everyone realized the risk we were running with seizure. With aluminium pistons we have to use three times the amount | ||