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.