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).
Valve noise and bounce issues, detailing valve failures and proposed design modifications.
| Identifier | ExFiles\Box 96\2\ scan0089 | |
| Date | 4th December 1935 | |
| -2- Hs{Lord Ernest Hives - Chair}/Swdl.{Len H. Swindell}18/KW.4.12.35. The valve noise at present on this set is almost solely confined to the exhaust valve on seating, and can be cured by applying a sideways force to the spring. A set of valves are being prepared in S/SLV and KE, chromium plated, with smaller valve guide clearances, which should give some results in respect of this trouble. Referring back to valve bounce with the latest exhaust valves E.87584, these valves are the outcome of the two failures during a 10,000 miles test, where the heads broke away from the stems, the valves being to E.86289. In the latter case the stems were .3412" dia. with a .141 dia. lightening hole, the resultant area being .0759 sq.in. and the weight of the valves, 2.66 ozs. Later, similar valves but without the lightening holes, were fitted, increasing the cross-sectional area to .0915 sq.in. and the weight to 2.91 ozs. Although no breakages have occurred with this latter valve, the increased area and proportionate strength increase does not appear to have a sufficient safety factor to ensure that we shall have no further trouble. The latest valves, E.87584, have solid stems .3725" dia. giving a cross-sectional area of .1085 sq.in., the weight being 3.21 ozs. Several strengths of plunger return springs were tried without any appreciable effect on the bounce speed, including the following :- E.87554 - 7 lbs., E.86880 - 5¼ lbs., and E.85321 - 4½ lbs. It has been reported that stronger plunger springs reduce a high speed tappet noise, but this has to be confirmed in conjunction with .001" or .0015" plunger clearances. We cannot pick this period out on the test bed. Other outstanding troubles with the self-adjusting tappets are as follows. (a) Spring ring which retains the plunger valve spring has in several cases come adrift and we have an alternative scheme to Hs.{Lord Ernest Hives - Chair}2215 now being prepared for test. | ||