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).
Series of experiments modifying cam and tappet faces to ensure rotation and reduce wear.
| Identifier | ExFiles\Box 158\4\ scan0229 | |
| Date | 10th May 1938 | |
| -2- The resultant offset moment was not sufficient to ensure rotation with the full width cam (.650) there being a cam width of .425 tending to rotate from the CL of the tappet and an opposing width on the other sides of the CL of the tappet of -.25. Without rotation the above tappets began to show signs of scuffing on the face. The second experiment consisted of machining the front face of the cam back to the CL of the tappet, that is the aforementioned opposing cam width of .225, thus leaving an effective cam width of .425 to effect rotation. This arrangement was quite satisfactory and gave positive rotation. The third experiment was to machine the front face of the cam down to having a cam width of .300 according to Fig.II of W.D.30 which is vertical tappet flat face reproduction of the standard raith condition of inclined tappet and conical face, both in width of cam and moment of rotation. As expected this arrangement gave the same characteristic as raith III. The fourth experiment was carried out in accordance with the scheme W.D.128 which consisted of the full width cam (.625) machined back at the tips of the cams to induce rotation and which it has done satisfactorily. Summarising these result if it will be of any advantage to production the promising results we have had with the vertical tappet and flat face we will continue running and likewise equip the next 15,000 miles test engine. From our point of view it has the advantage of line contact throughout the valve lift against the present raith of line contact on the base circle and at full lift but point contact at all parts lifts. The scheme we recommend is our second experiment where the cam front face is machined back to the CL of the tappet, leaving a cam width of .425 which compares with .300 effective width of the existing raith arrangement and has therefore less unit loading to reduce wear. | ||