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).
The causes of valve burning, particularly comparing post-war and pre-war designs with different valve seat angles.
| Identifier | ExFiles\Box 35\3\ scan 043 | |
| Date | 12th July 1923 | |
| -2- B.B. 403A (40 H) (SL 12 12-7-23). J.H., D.{John DeLooze - Company Secretary} EXPERIMENTAL REPORT. Expl. No. 2764 REF: Hal/LGS.8.23. burning the valve is when the tappet lifts the valve .017" off its seat. Under these conditions we were able to burn a section of the valve head entirely away. It is interesting to note that we have had no cases of failures of the exhaust valve during bench tests, dynamometer tests or experimental tests except where we have purposely made adjustments to bring it about. It is therefore our opinion that the comparatively few failures which occur on customers cars are due to a combination of points. Our tests prove that if there is any excessive slack in the valve guide so that the valve either by a faulty valve spring or tappet not being square is tilted on one-side, this would make the valve burn more easily. We think this is the reason why the valves which have failed appear only to have been locally over-heated. Our tests have shown the reasons why the post-war valve is worse than the pre-war is because :- (1) Angle of Valve Seat. Given the same valve lift, the 30° angle valve will allow more gas to pass than the 45° angle valve. This means that if the valve is held off its seat by the tappet the same amount in both cases, the 45° valve will be the hottest. In the case of a slack guide and the valve being tilted sideways, the 45° valve will have more of its seat in contact than the 30° angle valve under the same condition. Also, when the valve becomes red-hot, the head expands and owing contd:- | ||