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).
Test report on a scheme to prevent a valve dropping into the cylinder upon spring failure, with results and proposed modifications.
| Identifier | ExFiles\Box 88\4\ scan0063 | |
| Date | 16th May 1934 | |
| To SG.{Arthur F. Sidgreaves - MD} c.c. to Nor. c.c. to E.{Mr Elliott - Chief Engineer} c.c. to Ry. c.c. to Da.{Bernard Day - Chassis Design} c.c. to Bn.{W.O. Bentley / Mr Barrington} Ha/R.Mths.{Reg Matthews}11/KW.16.5.34. BENTLEY VALVES TO LEC.3873. This scheme is to prevent the valve dropping into the cylinder in the event of a valve spring failure. In order to test the scheme we fitted a valve spring with one coil ground half way through in order that it break, and then ran the engine at 4000 r.p.m. We also fitted through the sparking plug hole of this cylinder a steel bar which would prevent the valve falling should the scheme fail. After breaking the valve spring we ran the engine for a short time at high speed until the top washer fell and the wedges flew out. The valve then dropped, but only as far as our bar would let it. On examining the valve after the test we found that the spring ring was still in its groove on the valve stem but the valve had dropped so far that the ring had been forced a considerable way through the valve guide packing and only the bar that we inserted in the sparking plug hole had prevented it coming in contact with the top of the valve guide. We then removed the cylinder head and also removed the valve packing and let the valve fall until the spring ring was in contact with the top of the valve guide. With these conditions only a very light blow was necessary on the valve stem to force the spring ring out of its groove. In order to overcome this trouble we counterbored the top of the valve guide slightly over the outside diameter of the spring ring for a depth of .062, and with this modification we failed to force the ring out of its groove with quite heavy blows with a hammer on the valve stem. The outside diameter of the ring we measured was .375" and we counterbored the valve guide .383. This modification of course will let the valve fall .062 more so that the valve may hit the Piston Crown, and in order to overcome this the ring will have to be lowered approximately .062. Will E.{Mr Elliott - Chief Engineer} make the necessary modifications to the design. Ha/R.Matthews. | ||