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.