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 results on Phantom III valve gear to address valve bounce by adjusting spring loads and plunger clearances.
| Identifier | ExFiles\Box 96\2\ scan0088 | |
| Date | 4th December 1935 | |
| To E.{Mr Elliott - Chief Engineer} Hs{Lord Ernest Hives - Chair}/Swd1.18/KW.4.12.35. Phantom III Valve Gear. We have tested an up to date set of tappets with the 8.75 : 1 eccentric ratio to LeC.4427 in conjunction with the latest large stem diameter exhaust valve LeC.4711. As fitted with Hs.{Lord Ernest Hives - Chair}1827 inner and E.86364 outer double valve springs, having a seat load of 58 lbs., together with plungers having a diametrical clearance of .001", valve bounce occurred at speeds in excess of 4,000 r.p.m. This we found was confined to the exhaust valve due to the increase in weight. By fitting Hs.{Lord Ernest Hives - Chair}1828 inner springs in place of E.86364 springs, which increases the seat loading by 7 lbs., to 65 lbs., we were able to run up to 4250 r.p.m. before bounce occurred. A set of outer springs have been instructed to Rm.{William Robotham - Chief Engineer}24, which in conjunction with the Hs.{Lord Ernest Hives - Chair}1828 inner springs should give a seat loading of 75 lbs., which we are hoping will raise the bounce speed to 4500 r.p.m., the maximum speed at which all our tests have been carried out. Other than by increasing the valve spring loading, the bouncing speeds we have found, by previous tests, can be brought down by increasing the leakage factor of the plunger. As previously stated, the plungers in this test have a clearance of .001", which in conjunction with the 8.75 eccentric ratio give an approximate equivalent leakage factor to the original combination of .0015" clearance with the 12 : 1 eccentric ratio. Any increase in the plunger clearance increases the effective running clearance and so makes the valve seating noise greater, and with this in view we do not want to increase the plunger clearance any more than necessary and what is a practical production job. Included in our future tests is a trial with plungers having a .0015" diametrical clearance. | ||