First, take up all “lost motion” and place the engine on the center. This is done by putting the wrist-pin, crank-pin and center of the main shaft in line. To do this accurately, turn the engine until the cross-head is about half an inch from the end of its stroke, and mark the position of the cross-head on the guide.
Place a marker against the edge of the fly-wheel, and make a mark on the fly-wheel opposite the marker, then turn the engine until the cross-head completes the stroke and comes back to the mark made on the guide.
The crank will now be as much below the center as it was above before. In this position make another mark upon the fly-wheel opposite the marker.
Now, midway between the two marks on the fly-wheel, when turned opposite the marker will put the engine on dead center. Next, remove steam chest cover and place the eccentrics about one-quarter turn ahead of the crank in the direction the engine is to run. If the engine is to run “over”, place the throw of eccentric up. If it is to run “under”, place throw of eccentric down.
Then set eccentric carefully at such a point that the valve will have just commenced to open say ¹/₃₂ of an inch on the end that should be taking steam. If there is a rocker arm used which reverses the direction of the motion, i. e., making the valve stem move in the opposite direction from the eccentric rod, the eccentric must be set behind the crank, when the engine is to run “over”, in order that the port may open as the engine turns forward; but if a rocker arm is used merely to multiply the motion without changing the direction, proceed as though there was no rocker arm at all. Next, measure the “lead” which you have given to the valve at end which you have set. This is easily done by pushing a wedge-shaped stick or piece of soft wood into the port opening. The edge of the valve and port will mark the distance it goes in. Turn the engine upon the other center, which will be found as before described, and see if the lead is the same at both ends of the valve. If it is, the engine is properly set. If it is not, move the valve on the stem towards the end having the greatest amount of lead, a distance equal to one-half the difference in the leads. If the equalized lead is more than is necessary, set the eccentric back a little.
There are numerous methods of attaching the stem to the valve. A common way is with jam-nuts. With this arrangement it is only necessary to turn back the nuts on end towards which the valve is to be moved, an amount which will allow the given movement; then, turn the other nuts until the valve is forced into place to travel equal distance both ways from its center position. When the stem screws directly into the valve, the connection to the rocker arm or guide must be taken apart, and the stem screwed into or out of the valve enough to give it the required position. After the valve is set, replace the steam chest cover, and secure the eccentric perfectly tight with the set-screws, to prevent it from slipping.
SETTING SLIDE VALVE OF
REVERSING ENGINES.
The Link Reverse Being Used.
First, see that all the lost motion in the connecting rod, pillow block bearings and cross-head is taken up; then throw the reverse lever in last notch in quadrant, which would allow the engine to run “over”; then, remove the steam chest cover. Next, loosen eccentric (the eccentric rod of which is in direct line with the valve rod), turn the eccentric completely around, and watch the valve to see whether it laps the steam ports exactly the same amount at both ends, or travels an equal distance from its central position both ways. If it does, the valve is in proper position upon the rod. If it does not travel equally, the valve must be made to do so by adjusting it upon the valve rod, which is done by lengthening or shortening the rod, by use of jam-nuts, with which the rod is usually furnished. After this is done accurately, place the engine upon its forward center. This is done by turning the engine forward until the cross-head is about ½ inch from end of its stroke and mark the position of the cross-head upon the guide; then, with the use of long tram or dividers, mark from any convenient point on the frame to the band wheel or disc, and mark both points with prick-punch. Again turn the engine forward until the cross-head completes its stroke and comes back to the mark made on the guide; then, with the same long tram or dividers, mark the band wheel or disc as before from the prick mark already made on the frame.
Midway between punch marks on band wheel or disc, which can be found by use of dividers, will give the point which will place the engine on the “center” by turning engine back far enough to allow the long tram or divider to fit in punch mark on frame, and center punch mark on band wheel or disc. Now turn the eccentric over in the direction in which the engine is to run, until the valve gives the proper amount of lead on the front of steam port, which is about ¹/₃₂ of an inch, and fasten eccentric with set-screw. Then turn engine over the way it is to run, and place it upon its back center. This is done exactly as before described for forward center, and if the valve is properly proportioned, it will give the required ¹/₃₂ of an inch lead on the back steam port, and valve will be properly set for running in this direction.