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).
Analysis of engine cylinder head designs, including overhead camshafts, four valves per cylinder, and hydraulic tappets.
| Identifier | ExFiles\Box 133\2\ scan0105 | |
| Date | 19th November 1934 | |
| -2- Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}12/KW.19.11.34. An analysis of the best we can do with the present standard head, the high power head and the Rudge head will indicate what we may expect in the way of improved efficiency. An overhead camshaft drive does not necessarily mean increased cost. On the credit side of the overhead camshaft would be the elimination of the existing bottom tappets, push rods and tappet springs. On the debit side we should add a top camshaft drive and drive shaft; also we should anticipate that to get the full benefit from the overhead camshaft we should require four valves per cylinder. However, we feel that if the four valves per cylinder give the increase we expect we shall want them whether we have an overhead camshaft engine or a push rod engine, only in the latter case they will be very difficult to operate. There are the minimum of limitations as to the highest compression ratio that can be used with the pent-house head. It may not be so easy to work at high ratios with the power and ramp type heads. We shall require one Cadillac type hydraulic tappet adjuster for each pair of valves. We believe that whatever poppet type of valve mechanism we adopt, it will be necessary to have at least two hydraulic tappet adjusters per cylinder. Even on side valve engines in America, where cost is a primary consideration, they are finding that hydraulic tappet adjusters are worth their cost for the additional valve life they give. Having four valves per cylinder and eliminating push rods and bottom tappets with their respective return springs should decrease the loads on the camshaft by more than 30% and hence make for silent durability. We should anticipate that two overhead exhaust valves with stellited faces to them would run almost indefinitely without requiring re-grinding. | ||