SCIENCE OF THRESHING. 135 



/;. While the engine is in this position, take a tram, 

 d, or a common pair of dividers, and adjust its scratch 

 point at about the height of the center of the crank 

 shaft above the floor. Place one end on the floor or 

 engine bed and with the scratch point make a mark, e, 

 upon the edge of the flywheel. The engine will not 

 be on the center exactly; the crank pin will be 

 slightly above the center. Turn the engine in the 

 direction of the arrow, x, until the edge of the cross- 

 head comes even with the mark, b, on the guides. 

 The flywheel will have made nearly a revolution and 

 the crank pin be the same distance below the center 

 that it was above it. The tram point will now make 

 a new mark, e , on the rim. Make a mark on the rim 

 midway between the mark e and the mark e t and then 

 turn the engine until the center mark, f, is opposite 

 the tram point. The engine is then exactly on its 

 dead center. Find the dead center at the opposite 

 end in the same way. 



To set the valve, put the engine on its dead center, 

 place the valve on its seat and connect it with the 

 valve rod; shift the eccentric on the shaft until the 

 valve has the required lead. Turn the engine the 

 way it is to run, until it is on the other dead center. 

 If the lead is the same as at the other end of the 

 throw or stroke, the valve is correctly set; if it is not, 

 the valve rod must be lengthened or shortened until 

 the lead at either end is the same. If now the lead 

 be too much, the eccentric may be shifted back on the 

 shaft; if too little, it may be shifted ahead. 



If the engine has a reversing gear, the reverse 



