Locomotive Engine Running and Management

by Angus Sinclair

ANGULAR ADVANCE OF ECCENTRICS.

The change made on the eccentric location is to advance it from e to F, being a horizontal distance equal to the extent of lap and lead, and known as the angular advance of the eccentric. The centers F and B represent the full part, or “belly,” of the forward and back eccentrics in the position they should occupy, where a rocker is employed, when the piston is at the beginning of the backward stroke. It will be perceived that the eccentrics both incline towards the crank-pin, and the eccentric which is controlling the valve follows the crank-pin. Thus, when the engine is running forward, F follows the crank: when she is backing, B follows.

It is a good plan for an engineer to make himself familiar with the proper position of the eccentrics in relation to the crank, for the knowledge is likely to save time and trouble when any thing goes wrong with the valve-motion. With this knowledge properly digested, a minute’s inspection is always sufficient to decide whether or not any thing is wrong with the eccentrics.