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).
Proposal to increase the bore of the 20 HP engine to 3.250 inches.
| Identifier | ExFiles\Box 103\4\ scan0034 | |
| Date | 17th April 1929 | |
| X5650. R.{Sir Henry Royce} from E.{Mr Elliott - Chief Engineer} SECRET E2/M17.4.29. c. to Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} PN.{Mr Northey} Hs.{Lord Ernest Hives - Chair} By.{R.W. Bailey - Chief Engineer} EP.{G. Eric Platford - Chief Quality Engineer} 20 HP. PERFORMANCE AND 3.25 BORE Further to our memo. E1/M15.4.29. we now suggest that the bore of the 20 HP. should be put up to 3.250". We believe we can make a good job of this without extensive redesigning, and with no more altered parts than are called for by the new head, except for larger pistons. Whether we have new connecting rods or not is a moot point, but we did call for a longer rod in connection with the pedestal piston for this engine, and we should certainly prefer the longer one. There is no prospect of increasing the stroke unless we redesign the engine, as all available crankcase space was used up in increasing the crankpin diameter from 1.5 to 1.75. 3.25 bore gives 17.5% increased capacity, 48% of SS.{S. Smith} capacity, and 25.3 R.A.C. rating. The stroke bore ratio would be 1.4 as compared with 1.3 on the SS.{S. Smith} From the point of view of cylinder head design we would welcome an increase in capacity as it provides more room for water cooling, also we would be able to obtain a higher degree of turbulence in the charge which we believe would be beneficial. We have nearly ready drawings of the alterations for putting the bore up to 3.250" proposed. E.{Mr Elliott - Chief Engineer} | ||