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).
'Spectre' engine's big end construction, comparing it with American designs.
| Identifier | ExFiles\Box 93\5\ scan0090 | |
| Date | 11th May 1933 | |
| To E.{Mr Elliott - Chief Engineer} from Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} 317 Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}3/KT.11.5.33. SPECTRECodename for Phantom III BIG END CONSTRUCTION. With regard to the big end construction, it would be interesting to know the actual increase in engine length due to side by side rods. We have always considered one of the merits of the 12 cyl. engine over the 6. is its reduced length giving increased bodyroom and less "jellying" tendency. Most of the Americans use a four bearing crankshaft, and even so where side by side rods have been used on the Cadillac the big end width was "cut" to reduce the engine length. The Cadillac dimensions we got while we were in America were - Pin dia. 2.5" Journal 2.625" Total width of pin 2.00" Width of each big end 1.00" Overall length of crankshaft from back flange to beginning of crankshaft damper taper 32.00" They were in considerable trouble with big ends, in fact these were their main troubles on both 12's and 16's eighteen months ago. It would be interesting to know the smallest crank pin dia. which would enable a blade or articulated type rod to pass through the cylinder bore. Since we never run into a master period on a 12 cyl. and whatever size the shaft, the half speed period will always be in the running range we cannot see the advantage of a large diameter crankshaft. Certainly we found on a Phantom, where we ran above the critical crank speed that the engine was astoundingly smooth. One other point is heat to the oil, which, from Riley's results and our own, is definitely increased by large diameter crankshafts. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} | ||