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).
Tests on Cadillac type automatic tappets for the Phantom II to investigate high-speed valve float and power loss.
| Identifier | ExFiles\Box 17\6\ Scan239 | |
| Date | 15th June 1934 | |
| To E.{Mr Elliott - Chief Engineer} c. to Wor.{Arthur Wormald - General Works Manager} c. to By.{R.W. Bailey - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} Hs{Lord Ernest Hives - Chair}/Swdl.{Len H. Swindell}1/KW.15.6.34. Cadillac Type of Automatic Tappets for Ph.II. Tests have been carried out in an endeavour to locate the cause of valves being held open at the high speeds; resulting in loss of power. From the results obtained with various types of springs, the trouble appears to be a combination of spring surge and valve bounce, so that when separation takes place the eccentric follows up, taking up this amount of separation. The speed at which the trouble starts is more directly affected by small differences in cam contour than by appreciable differences in spring loading and rating. Our present position is that we can run up to 3400 R.P.M. before losing power by using the original Ph.II camshaft (E.80070), Hs.{Lord Ernest Hives - Chair}1301 valve springs packed up .150 and giving a seat loading of 85 lbs. and full lift loading of 165 lbs., the rating being 188 lbs/inch, in conjunction with standard valves. The figure for standard valve springs and camshaft (E.82448) is 3100 R.P.M. Camshaft Comparisons. Running with E.82448 camshaft and a certain set of 260 lbs/inch rating springs with a seat loading of 65 lbs., the exhaust valves started opening at 2700 R.P.M. By packing the exhaust springs only, to a seat loading of 85 lbs., we were enabled to run up to 3150 R.P.M. where it was still the exhaust valves giving trouble, the inlet valves being O.K. With this condition of springing the camshaft E.80070 was fitted with almost reverse results, power falling off at 3150 due to opening of the inlets, the exhaust valves now being O.K. at this speed. Following this the inlet springs were packed out similar to the exhausts, giving 85 lbs. seat loading and the speed was increased to 3300 R.P.M., where the power fell off through exhaust valves opening. | ||