52 SCIENCE OF SUCCESSFUL THRESHING 



taking off the connecting-rod, make a scratch across the 

 wedges and the rod end, so that in putting them back the 

 wedge may be set in the same position as before. 



As the pressure is nearly all endwise on the rod, the 

 holes in the brasses will tend to wear in an oval shape, so 

 that when the boxes are tightened, they will bind at the top 

 and bottom, causing them to heat, while they still pound 

 endwise. To obviate this difficulty, the boxes should be 

 "relieved" at the top and bottom by filing with a half- 

 round file. They should not touch the pin for a distance 

 of one-half to three-quarters of an inch each side of the 

 joint. In time, the brasses will have worn so much that 

 the wedge strikes against the top. Shims made of sheet- 

 iron of the proper thickness must now be inserted. These 

 should be put in on both sides of the brasses so as to not 

 change the length of the rod, which would make it neces- 

 sary to re-divide the clearance. 



It is best to take off the connecting-rod when the en- 

 gine is cold; if it be taken off when the boiler is under 

 steam pressure, and the throttle should accidentally be left 

 open, or should leak, the piston may be driven through the 

 cylinder with force enough to do serious damage. 



The Shoes of the Cross-Head are adjusted by loosen- 

 ing the four cap screws, (E), and screwing up the four set 

 screws, (F), to force the shoes against the guides. This 

 will leave a space between the shoes and cross-head into 

 which sheet-iron shims should be inserted. If these shims 

 be of the right thickness to just fill the space, loosening the 



