THE VALVE-GEAR. 8l 



lever in the last notch at either end of the quadrant. Now, 

 with a scratch-awl having a very fine point, make scratches 

 on the valve seat, showing the extreme position of the valve 

 at each end of its travel as the fly-wheel is revolved. Meas- 

 ure from the marks to the outside edges of the steam ports, 

 and, if there be any difference, divide it up by lengthening 

 or shortening the eccentric-rod, that is for the time being, 

 moving the valve. The length of the other rod is found 

 in the same way, the reverse-lever being at the opposite end 

 of the quadrant. If the engine be marked and you have the 

 "tram" for placing it on the centers, as already explained, 

 proceed to set the valve as follows : After the lengths of 

 the eccentric-rods are correctly adjusted, according to the 

 method already given, place the engine on one of its dead- 

 centers, say. the head one, and set the reverse lever in the 

 last notch at either end of the quadrant. The valve should 

 now be in such a position that the port leading to the head 

 end of the cylinder should show a "lead" equal to the thick- 

 ness of an ordinary playing card. The amount of lead 

 may be varied by rotating the eccentric hub around the 

 shaft. Rotating it in the direction in which the engine is to 

 run increases the lead and moving it in the opposite direc- 

 tion decreases the lead. When you have obtained the desired 

 lead, place the engine on the other dead center and see if 

 the lead be the same. If it be not, the valve-stem should be 

 lengthened or shortened, (by means of adjusting nuts), until 

 it is the same. If, after dividing the lead, there be too 



