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).
The design and adjustment of valve springs and tappet clearance in engines.
| Identifier | ExFiles\Box 147\1\ scan0031 | |
| Date | 18th March 1935 guessed | |
| 2. valve is under the direct control of the valve spring in the usual way. The valve spring may be designed so as to satisfy two different sets of conditions. For instance it may be designed in accordance with current practice namely so as to be strong enough to bring about the efficient closing of the valve and nothing more. In this case, if the loading of the valve spring so arrived at, is less than that of the outer spring washer then the usual clearance gap will result between the head of the tappet screw and the cam follower, or rocker arm, as the case may be. If however the loading of the valve spring is by design made greater than that of the outer spring washer then the latter will yield under its pressure and the clearance gap will close up as soon as the valve touches its seating. The result is a rationally spring loaded valve and tappet assembly functioning without shock and therefore with the minimum amount of wear and noise. It has already been explained that the parts are assembled in the first instance so as to leave a clearance gap which is considerably greater than will ultimately be required. A final adjustment is therefore necessary and this is done by unscrewing the tappet screw until it just begins to grip a feeler gauge of the proper thickness which has been inserted for this purpose. But if the loading of the spring washers and valve spring is as already suggested in the second alternative then tappet clearance cannot be adjusted until the tappet screw has been relieved of the valve spring pressure. In side valve engines where the valve head is readily accessible this may be done by lifting the spring with one of the usual spring lifting cramps abutting on the valve head while its other end, which is formed with a slot which spans the flats on the tappet screw head, engages the locking washer and so lifts the valve spring. In the case of overhead valves the cramp, or a pair of spring lifting pliers, may be made with one jaw to be forced between the coils of the valve spring and formed with a slot to engage a groove in the valve stem just above the hexagon collar. The other jaw engages the end of the valve spring as before. In this way the end coils of the spring are compressed, the tappet screw is relieved of pressure while the valve remains held down on its seating by spring pressure. The tappet clearance can now be measured and adjusted to the required amount. When this has been done the tappet screw and valve are locked relatively to one another by bending down those segments of the locking washer which overlie the flats in the head of the tappet screw. A.{Mr Adams} BUCKLEY, F.C.G.I., M.{Mr Moon / Mr Moore} INST. C.E., M.{Mr Moon / Mr Moore} INST. W.E. CONSULTING ENGINEER, 84 VICTORIA STREET, S.W.1. | ||