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).
Tests of a Wraith III 'mock-up' unit, detailing modifications to the cylinder block and valve gear.
| Identifier | ExFiles\Box 6\6\ 06-page256 | |
| Date | 19th August 1937 | |
| By, from Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}1/AP.19.8.37 c. to Es. c. to De. c. to Hx. c. to MO. 600 WRAITH III. UNIT. The following is a report of our tests on the above unit as carried out to-date, useful information being obtained by the assembly of a 'mock-up' engine now in 24.G.VI. and consisting of the following construction. Wraith III. up to the joint face of the crankcase and above as 25/30, including cylinder block, head and through studs from the crankcase. In comparison with normal Wraith III, this Mock-up unit generally was smoother, more free from periods and gave quieter valve gear operation. Based on these results and for the following reasons the Wraith III 'loose liner' cylinder block has now been modified to the solid block construction with 'through' studs as per 25/30 and Bentley, to Loc.5778. (a) Studding of Wraith III. block with nuts inside crankcase rendered its removal an almost complete dismantle of the unit. (b) Improved knowledge now available with regard to overcoming difficulties of casting and 'high scrap' with the solid type of block. (c) Long experience of this type of construction on Bentley and 25/30. Regarding the quiet valve gear obtained on the 'mock-up' unit, this by virtue of 25/30 rockers has a lift of .340 as against .400 on Wraith, weaker springs and lighter valves, but with identical camshaft and tappets. From these results, rockers are being produced, having a .350 valve lift by which means we anticipate improvement regarding tappet noise periods at present experienced on Wraith III. with the .400 lift and ability to use weaker springs or at least retain existing with a greater margin of safety against failure. continued | ||