However well each may understand his business, in one respect all engineers are in perfect harmony; that is, in hating to encounter trouble with the valve-gear on the road. The valves being the lungs of the machine, any injury or defect to their connections strikes at a vital organ. With a good valve-motion, and valves properly set, the steam is distributed so that nearly an equal amount is admitted through each part in regular rotation; the release taking place in even succession. This makes the exhaust notes uniform in pitch and period. A sudden departure from this uniformity indicates that something is wrong with the valve-motion. It should be the signal to stop, and institute a searching examination. In doing so, avoid jumping at conclusions regarding the cause of the irregularity, and coolly examine, separately, each part whose motion influences the valve-travel.
A WRONG CONCLUSION.
Fred Bemis missed his luck by jumping too readily at conclusions. Something happened to his engine; and he stopped by compulsion, and found it would not move either way. He felt certain that both eccentrics on one side had slipped; and, considering himself equal to setting any number of eccentrics, he got down, and fixed them in what he supposed was the proper position. But, on trying to move the engine, he found it still refused to go. He kept working at those eccentrics without result till his water got low, and he was compelled to dump the fire; the consequence being, that the engine went cold, and was towed home. When an examination was made, it was found that a broken valve-yoke was the cause of trouble.
LOCATING DEFECTS OF THE VALVE-MOTION.
When any thing goes wrong with the valve-motion, the first point of investigation is, to find out which side is at fault. This can be ascertained by opening the cylinder-cocks, and giving the engine steam. With the reverse-lever in forward motion, the forward cylinder-cocks should show steam when the crank-pins are traveling below the axle, and the back cocks should blow when the pins make their similar revolution above the axle. Any departure from this method of steam distribution will make one side work against the other. When the engineer has satisfied himself on which side the defect lies, he will do well to thoroughly examine the eccentrics with their straps and rods, the links with their hangers and saddles, the rocker box and arms with all the bolts and pins connecting these articles. What might be regarded as a trifling defect, sometimes makes an engine lame. I have known a loose valve-stem key put an engine badly out of square. Eccentric-rods, slipping, often produce this effect. When the eccentrics are found in the proper position, the rocker-box secure in the shaft, and all the bolts, pins, and keys in good order, and in their proper positions, the fault may be looked for in the steam-chest.
POSITION OF ECCENTRICS.
With engines where keys are not used to secure the eccentrics to the shaft, their slipping on the road is a common occurrence. Eccentric-strap oil-passages getting stopped up, or neglect in not oiling these straps or the valves, puts an unnecessary tension on the eccentrics, which often results in their slipping on the shaft. Engineers ought to mark the proper position for eccentrics on the shaft; so that, when slipping happens, it can be adjusted without the delay that often occurs in calculating the right position. When the crank-pin is on the forward center, the body of the go-ahead eccentric is above the axle, and the body of the back-up eccentric is below the axle, each of the eccentrics being advanced about 1/16 of the revolution from the right angle position towards the crank-pin; or, to state it more accurately, the center of the eccentric is advanced a horizontal distance to equal the lap and lead of the valve. If the valve had neither lap nor lead, the eccentrics would stand exactly at right angles to the crank. As it is, both of them have a tendency to hug the crank; the eccentric which regulates the distribution of steam following the crank. Every engineer should familiarize himself with the correct position of eccentrics, so that, when trouble happens with the valve-gear on the road, he will experience no difficulty in grappling with the mishap.
METHOD OF SETTING SLIPPED ECCENTRICS.
The slipping of one eccentric is a trifling matter, which can be quickly remedied if the set screws are in a position where they can be reached conveniently. If it is a go-ahead eccentric, set the engine on the center of the disabled side,—no matter which center,—put the reverse-lever in the back notch of the quadrant, and scratch a line with a knife on the valve-stem close to the gland. Then put the lever in the forward notch, and move the slipped eccentric till the line appears in the point where it was made. Fasten the set screws, and the engine will be found true enough to proceed with the train. Care must be taken in moving the eccentric to see that the full part is not placed in the same position as the other one, or they will both be set for back motion. A back-up eccentric slipped, while the go-ahead one remains intact, can be adjusted in a similar way; the scratch on the valve-stem being made with the engine in full forward motion, and the adjustment of the eccentric done in full back motion. The philosophy of this method is, that the valve is in nearly the same position at the beginning of the stroke for the forward or back motion; and the position of the eccentric, which has not moved, is used to find the proper place for the one which slipped. Should the unusual circumstance of both eccentrics on one side slipping overtake an engineer, he will have to pursue a different method of adjustment. The most systematic plan is to place the engine on the forward center, and set the go-ahead eccentric above the axle, and the back-up eccentric below the axle. With the reverse-lever in the forward notch, advance the top eccentric till the front cylinder-cock shows steam, which can be ascertained by blocking the wheels, and slightly opening the throttle. That will put the go-ahead eccentric near enough to the proper position for running. For the back-up eccentric, pull the reverse-lever into back motion, and turn the eccentric towards the crank-pin till steam appears at the front cylinder-cock; and that part of the motion will be right. Or the back-up eccentric can be set by the forward eccentric in the manner described where one eccentric has slipped.