Locomotive Engine Running and Management

by Angus Sinclair

Thus: Turn the wheels forward till the cross-head reaches within one-half inch of its extreme travel, as shown in [Fig. 18]. From a point a on the guide-block, extend a tram on the cross-head, and mark the extreme point reached b. Put a center punch-mark c on the wheel-cover, or other convenient fixed point, and from it extend a tram on the edge of the tire, and scratch an arc d. Now, with tram in hand, watch the cross-head, and have the wheels moved forward slowly. When the cross-head passes the center, and moves back till the tram extending from a will reach the point b, stop the motion. Again tram from the wheel-cover point, and describe a second arc on the tire, which will be at e, now moved to the position which d occupied when the previous measurement was taken. With a pair of dividers bisect the distance between d and e. Mark the dividing point C with a center punch, and put a chalk ring round it. When the wheel stands so that the tram will extend from c to C, the engine will be on the forward dead center.

All the other centers must be found by a similar process.

TURNING WHEELS AND MOVING ECCENTRICS.

When a measurement is going to be made for fore gear, the wheels must be turned forward; and, when it is for the back gear, they must be turned backward. Enough movement of the wheel must be given to take up the lost motion every time the direction of movement is changed. In moving an eccentric, it should also be turned far enough in the opposite direction to take up the lost motion.

SETTING BY THE LEAD OPENING.

Put the reverse-lever in the full forward notch, and place the engine on the forward center. If the lead opening in full gear is to be 1/16 inch, advance the forward eccentric till the point a ([Fig. 17]) on the valve-stem is that distance away from the tram point. Throw the reverse-lever into the full backward notch, turn the wheels forward enough to take up the lost motion, then turn them back to the forward center. Move the backward eccentric (if it needs moving) till the tram, extended on the valve-stem, strikes the same point that it reached for the forward motion. It will be noted here, that the valve occupies the same position for fore and back gear when the engine is on the center. Put the reverse-lever in the forward notch again, and turn the wheels ahead till the back center point is reached. Now tram the valve-stem again, and, if the lead opening be the same for both gears as it was on the forward center, that part of the setting is right. It is a good plan to go over the points a second time to prove their correctness. But it is not likely that the lead opening at the back end will be right on the first trial. Instead of having the correct lead, the valve will probably lap over the port, being what workmen call “blind,” or it will have too much lead. Let us assume that our valve is 1/16 inch blind. This indicates that the eccentric-rod is too long. We shorten the rod till the valve is at the opening point, and, on turning the engine to the forward center again, we will find that the valve there has lost its lead. But our change has adjusted the valve movement, so that on each center the valve is just beginning to open the steam-port. Advancing the eccentric to give one end 1/16 inch lead will now have the same effect upon the other end; and, assuming that the back motion has been subjected to similar treatment with a like result, the lead opening on that side is right. This process must now be repeated with the other side of the engine.

ASCERTAINING THE POINT OF CUT-OFF.

The lead openings being properly arranged, we will proceed to examine how the valves cut off the steam; for it is important that about the same supply of steam should be furnished to each cylinder and to each end of the cylinders. The angularity of the connecting rod tends to give a greater supply of steam to the forward than to the back end of the cylinder; but this inequality is, as has already been explained, usually rectified by locating the hanger-stud a certain distance back of the link arc.

To prove the cut-off, we will try the full gear first. Put the reverse-lever in the full forward notch, starting from the forward center, and turn the wheels ahead. The motion of our engine has been designed so that the cut-off in full gear shall happen at 18 inches of the stroke. With tram in hand, watch the movement of the valve as indicated by the stem marks. As the piston moves away from the forward end of the cylinder, the valve will keep opening till nearly half stroke is reached, when it will begin to return, slowly at first, but with increasing velocity as the point of cut-off is reached. When the point a, [Fig. 17], gets so that it will be reached by the tram extended from c, the motion must be stopped; as that indicates the point of cut-off. Now measure on the guide how far the cross-head has traveled from the beginning of the stroke, and mark it down with chalk. Then turn the wheels in the same direction past the back center, and obtain the cut-off for the forward stroke in the same manner. The cut-off for the other cylinder will be found in precisely the method described.

In addition to trying the cut-off in full gear, it is usually tested at half stroke and at 6 inches, or with the reverse-lever in the notches nearest to these points. Some men begin at the first notch, and follow the point of cut-off in every notch till the center is reached, and do the same for back gear.