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).
Aerolite and split skirt pistons, including details on grinding, and test bed results for cylinder heads and blocks.
| Identifier | ExFiles\Box 124\2\ scan0203 | |
| Date | 5th July 1940 | |
| -5- Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation}4/JMS.5.7.40. The equivalent Aerolite pistons for the same range of units are: P.485 (75 m/m) P.482 (3.50") Note. We have not catered for a 3.25" bore Aerolite, having used the stock split skirt pistons from Repair Dept. for 3.25" bore units. All the above five types are "flush top", and have tin- plated and "L" section rings incorporated in their assembly. The reason the grinding of the split pistons is to be done by our works is: The grinding of the Aerolite is purely elliptical, the flutes being so designed to cause the piston to go almost round at running temperature (they say). Our skirt grinding is eccentric off two diameters, and Light Production have no facilities for doing the complete job without special tackle. It should be considered worth while to test these split skirt pistons. We have tried before to get away from the specialised grinding, but have always had to come back to it on production, to get consistently quiet pistons over numbers of chassis in a given series. CYLINDER HEAD. On the test bed to date we have been able to find little difference between any of the variations of the basic design EB.3844. With pistons .030" down the bore we would say that the optimum compression ratio is 6.5:1. We believe, however, that the use of "flush top" pistons would raise this optimum ratio to 6.75:1. Also, we believe that this type of head is not so carbon conscious as the conventional combustion chamber, normally used on previous production series. CYLINDER BLOCK. On no other job have we concentrated so much effort with so little to show in result to date. In the files will be found the details of the various slight additions to an otherwise standard cast iron, these being known by names representing the "slight additions". Continued. | ||