Specification details for three different Wraith III engine units.
| Identifier | ExFiles\Box 155\2\ scan0223 | |
| Date | 3rd June 1938 | |
| -2- Rm {William Robotham - Chief Engineer} /Swd1.17/JH.3.6.38. Wraith III No.1 Unit (temporary in 29.G.VI). Obsolete type crankcase with loose liner cylinder block. No. 1, 2, and 3 Sheepsbridge. No. 4, 5, and 6 Phosphur chrome. AC.6 billet cast big end bearings .125 section of original type with keyed shims. Unhardened S/ZNX timing gears. 25/30 set of rockers. Vertical bottom tappets with flat faces. Camshaft original type with short toes. No. 1 - 4 cams full width .625 taper machined back at the tips to produce rotation. No.5 - 8. Cam width .400 front face of cam being on Q of tappet. No. 9 - 12. Front face of cam machined back to a cam width of .300 (Wraith condition). Reduced inertia flywheel with Rm. {William Robotham - Chief Engineer} 519 modification, including 10" B. & B. clutch. 8 valve springs Rs. {Sir Henry Royce's Secretary} 540 (S/CV) ) R.R. produced. 4 " " Rs. {Sir Henry Royce's Secretary} 540 Swedish ) Delco Ignition distributor. Wraith III No.2 Unit (Bore wear on rig) Obsolete type crankcase with loose liner cylinder block. Unhardened S/ZNX timing gears. Cylinder liners 1, 2 and 3 std. Sheepsbridge. " " 4, 5 and 6 Phosphor chrome. 3 Connecting rods with oil feed holes up centre blanked, gudgeon pins fed by splash. AC.6 big end bearings 1, 3 and 5 flanged. " " " " 2, 4 and 6 non flanged. .030 Klingerit cylinder head gasket. 1 - 6 EB.3236 valve spring Swedish wire. 7 - 12 EW.1428 S/CV. Delco ignition distributor. Wraith III No.3 Unit (24.G.VI). W/Mt. main brgs R.R.56 shims. | ||
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).