It is obvious that the eccentric may be moved around the shaft in place of across it, the distance its throw line requires to be moved being the same in either case.
To shift an eccentric so as to reverse the direction of engine revolution, all that is necessary is to place the crank on either dead centre and measure the amount of valve lead. Then loosen the eccentric from the crank shaft, and while the crank is stationary, move it around upon the shaft until it has opened the port full, and nearly closed it again, leaving it open to the same amount as it was before the eccentric was moved, or in other words, open to the amount of the lead.
Fig. 3384.
[Fig. 3384] represents a side elevation of a high speed wheel governor engine, designed and constructed by the Straight Line Engine Company of Syracuse, New York, the construction of the governor being shown in [Fig. 3385], in which r is the eccentric rod, the eccentric being carried in a lever strap pivoted at a, and connected at b to two links c and d, the former of which connects to the spring e, and the latter to the weighted lever f. The centrifugal force generated by the weighted end of f endeavors to move the eccentric inwards, and thus reduce its throw, which reduces the valve travel and hastens the point of cut off.
Fig. 3385.
On the other hand, the tension of the spring e acts to move the eccentric in the opposite direction, and maintain the full throw of the eccentric and maximum point of cut off. These two forces are so calculated in the design and proportion of the parts that under a maximum load the engine will run at its proper speed, while, if the load decreases, the action of f will hasten the point of cut off enough to allow for the decreased engine load, and thus keep the engine still going at the same speed.