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 concerning the warping of valve seats for the Wraith III cylinder heads.
| Identifier | ExFiles\Box 10\3\ 03-page143 | |
| Date | 20th June 1938 | |
| Rm.{William Robotham - Chief Engineer} from Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} Rm{William Robotham - Chief Engineer}/SwdlE/R.20.6.38. WRAITH III. Warping of Valve Seats. Further to our report Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}4/R.25.5.38., we have continued on this job with a view to giving the best recommendation for production where the first batch of 100 cylinder heads have been cast. As previously reported we have been testing out the small valve cylinder head, i.e., 1.3 dia. exhaust and 1.3 dia. inlet valves which compares with standard valves 1.4 dia. exhaust and 1.5 dia. inlet, the metal section between the valves being automatically increased from .250" to .350". From heads examined the section thickness appears to control the valve warping trouble, and as explained herewith our tests on the small valve head confirm this evidence. As a small valve head 15 hours general running on power curves, etc. had been carried out, and there was no sign of valve seat warping, a standard sized inlet valve was then fitted, and after running 3 hours on power curves, the inlet seats were slightly warped. Following this the exhaust valve was opened up to standard, and after a further 4 hrs running the inlet seats were warped fairly badly. In this condition both the inlet and exhaust ports had been taper machined as per scheme (1) of SSD.704, since which we have machined the ports standard in order to obtain the full story of the power comparison on the one cylinder head. Attached are power curves (S.43) and (S.42) taken on both the Wraith III and Bentley III units. On the Wraith III a maximum loss of 4 HP is registered with the small valves, whilst at the middle and low speeds the M.E.P. is slightly better than with standard valves. As tried on the Bentley III the maximum power is unaltered with the small valves but falls off at higher speeds by 3 B.H.P. at 4,250 R.P.M., and has a slight M.E.P. advantage at middle and low speeds. | ||