The Locomotive Of Today

The Engine : Valve S etting. 101 the under side of the frame, or other convenient adjacent point, and the tyre scribed with the other end ; then, again turning the wheels, the dead point is passed, and as the mark upon the crosshead is reached, the compasses exactly touching it, the wheels are stopped, and the tyre again marked from the same point. The distance between the two points upon the tyre is equally divided, and a pop made, and the wheels revolved until the trammel exactly enters it; at this point the slide bar is marked to indicate the dead centre, the distance between this point and the extreme position of the piston being the clearance. The other dead centres are found in exactly the same way, and the clearance marked for each one. Having indicated the dead points of the cranks, the lever is put over into full forward gear, and the wheels turned forwards, until one of the marks upon the tyre is reached by the point of the trammel entering the pop exactly; the wheels are then stopped, and the amount of port opening measured upon the valve spindle—this will be the lead for this port and gear. Turning the wheels again the next point is reached, and the lead taken in a similar way, and so on for the four centres. Reversing the engine into full backward gear, the wheels being turned backwards, the lead is measured for the same points in back gear. The reason for taking’ the lead in full gear is that with the shifting and straight link motions the lead is here least, it is therefore certain to be sufficient in the running positions. It is customary with some bnilders, instead of raising the driving wheels and turning them alone to set the valves, to place the engine upon a sufficiently long straight road over a pit and move it backwards and forwards so as to more exactly approximate the working conditions. If it shoulcl be found necessary through any inaccuracy in setting the eccentric sheaves, or if by an altered condition of service it is desirable to adjust the lead, it can only be done by shifting the eccentric sheaf round upon the axle, increasing the angular advance if the lead is to be increased, or decreasing it if the opposite result is desired. New keys are required in the sheaf shifted, and, if much altered, new sheaves may be wanted. Some makers, to guard against errors, set the valves before the keys are fitted, holding the sheaves by set screws only, and then when all adjustment is complete fitting the keys to sheaves and axle. It is always important to notice that all the parts of the motion that are to be coupled up to work together should be made to “ lead ” right for each other, and not be strained at ________