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.