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).
Dimensions and clearances of piston ring grooves for 25/30 and Wraith models.
| Identifier | ExFiles\Box 148\3\ scan0375 | |
| Date | 19th August 1938 | |
| -2- Rm{William Robotham - Chief Engineer}/Swd1.2/JH.19.8.38. several cars for experience over a long mileage. We should like the dimensionsof the ring grooves of the 25/30 and Wraith piston brought more into line with the Aerolite dimensions as the rings used on these pistons although of different strengths, have the same dimensions. The results of the above is that the 25/30 and Wraith piston rings have an up and down clearance in the grooves of .002 minimum to .0035 maximum, the Aerolites from size to .0025. On pointing out the size and size dimension of the Aerolites to Mr. Brookes he admitted of course that this was wrong, but stated that all the pistons and rings supplied have a clearance of .001 in the grooves and considered our clearances too high, which tends to induce sticking of the rings. We should therefore, like the groove dimensions of our pistons altering to give a nominal clearance of .001, with maximum to limits of .0025. Rm{William Robotham - Chief Engineer}/Swd1. | ||