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).
Technical report discussing piston clearances, internal strains, and gas leakage issues.
| Identifier | ExFiles\Box 35\2\ scan 224 | |
| Date | 12th April 1920 | |
| Contd. -4- HS{Lord Ernest Hives - Chair}1/LG12.4.20. went in a matter of .005" to .006". On the next set we hammered them before we machined them to get rid of the internal strains. We found then that the pistons remained up to size, in fact in some cases they were slightly larger when they were finally split. We find that in order to be absolutely free from piston knocks with the cast iron pistons it is necessary to have them either the same size as the cylinder bore or only .001" clearance. We know that the solid cast iron pistons they are using on Repair cars will knock sometimes when they have only .002" clearance. If we make these split pistons so that they are tight in the cylinder bore, they are quite alright as regards not seizing and being free under all conditions but they cause the engine to be very very stiff to turn when cold. We think this must be owing to the fact of the piston fitting completely into the cylinder bore - the area of the oil film to be sheared is much greater. The car we are running with these split cast iron pistons which were made the same size as the bore, it is practically impossible to turn it if left in the cold. 858 X.110. X.3751a. We have also been carrying out tests as regards leakage past the pistons.x Mr. Platford complains that on some of the cars he can distinctly hear, when driving the car an pulling it at very low speeds, the gas blowing past the pistons. Our tests show that the reason why we can hear the gas blowing past the present pistons is caused by the oil escape holes below the scraper ring. On the old pistons, the Contd. | ||