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).
Technical report on the warping of valve seats in Wraith III and Bentley cylinder heads.
| Identifier | ExFiles\Box 10\3\ 03-page133 | |
| Date | 26th May 1938 | |
| Rm.{William Robotham - Chief Engineer} from Pm/Swdl.{Len H. Swindell} Pm/Swdl.{Len H. Swindell}4/R.26.5.38. WRAITH III. WARPING OF VALVE SEATS. We have had several instances of valve seat warping in the proximity of the bridge between the exhaust valve and the inlet valve. The actual condition is that in this position the seating has sunk, or warped, as illustrated on the attached drawing Rm.{William Robotham - Chief Engineer}531, thus causing lack of compression and upset of the slow running. It was first brought to our notice during the 15,000 miles' test when the valves were examined after the sudden loss of clearance when the head had over-heated due to running retard, and was attributed to the latter reason. Since that time we have found the same trouble on several heads that have been on experimental chassis and test bed units. The first time it was regarded seriously was when we passed a unit off the test beds with excellent slow running which deteriorated after a short mileage and the valves were found not to be seating properly. On the same car, namely, 27.G.VI, the valve seats had again distorted after a further 3,000 miles' running. This trouble is confined mainly to the inlet valves, although present to some extent on the exhaust valves. We find that this condition exists on the majority of 4¼-litre Bentley chassis that come into the Repair, and has never become a serious complaint in that on this car the idling has never been good, which is the main feature affected by leaking valves. The above, however, is no excuse for not having tackled this job before, but now on Wraith it is much more vital in that everything possible has been done to obtain good idling, i.e., minimum camshaft over-lap and late static setting of the ignition, so that leaking seats do destroy good idling. We have examined a number of cylinder heads, namely, 25/30, 3½-litre Bentley, 4¼-litre Bentley and Wraith with the following results:- (1) That the 4¼-litre Bentley and the Wraith III have the same section of metal between the valves, which as shown on Rm.{William Robotham - Chief Engineer}531 is .250, and both suffer from valve seat warping, yet on the Bentley the distance of the water from the seat is 1.25" against 1.00" on the Wraith. | ||