THE VALVE-GEAR. 79 



the lever over to the road motion, will reduce this lead by 

 one-sixteenth, so that the leads will be nearly alike for the 

 road-motion. The "lead" should be obtained by adjusting 

 the length of the eccentric-rod, allowing the nuts on the 

 valve-stem to remain undisturbed. If the nuts on valve- 

 stem be loosened, the "draw-block" is liable to be tilted so 

 that the valve cannot leave its seat when necessary to let 

 water out of cylinder. 



It is best, after setting the^ valve, to go all over it again 

 from the beginning, and if all be found correct, the eccentric 

 may be set permanently by tightening both set-screws. These 

 are counter-sunk into the shaft, and if necessary, the depres- 

 sions may be changed by sliding the eccentric-hub to one 

 side, (after having removed the eccentric-strap), and chip- 

 ping them out with a round-nose chisel so that the deepest 

 part is in the required position for the set-screw. The eccen- 

 tric-hub and shaft should be marked, (as is done at the fac- 

 tory), with a cold-chisel, so that should the eccentric slip, 

 the slippage can be discovered and the eccentric readily 

 re-set. 



In any style of valve-gear the "lead" is changed by rotat- 

 ing the eccentric around the shaft. It will be seen that the 

 Woolf reverse, having but one eccentric cannot be adjusted 

 to change the lead, because if the lead be increased for engine 

 running "over," it will be decreased for engine running 

 "under," and vice versa. There is therefore but one position 

 for the eccentric. This is determined at the factory, and on 



