74 ROUGH-AND-TUMBLE ENGINEERING 



The brasses on the wrist pin and cross-head will probably 

 require your first and most careful attention, and of these 

 two the wrist or crank box will require the most; since 

 what is true of one box is true of boxes in general. It is, 

 therefore, not necessary to consider all boxes in instruct- 

 ing you how to handle them. We will take up the box 

 most likely to require your attention. This is the wrist 

 box. You will find this box in two parts or halves. In a 

 new engine you will find that these two halves do not 

 meet on the wrist pin by at least one-eighth of an inch. 

 They are brought up to the pin by means of a wedge- 

 shaped key. (I am speaking now of the most common 

 form of wrist boxes. If your engine should not have this 

 key, it will have something which serves the same pur- 

 pose.) As the brasses wear you can take up this wear 

 by forcing the key down, which brings the two halves 

 nearer together. You can continue to gradually take up 

 this wear until you have brought them together. You 

 will then see that it is necessary to do something, in order 

 to take up any more wear, and this "something" is to 

 take out the brasses and file about one-sixteenth of an 

 inch off from the edge of each brass. This will allow 

 you another eighth of an inch to take up in wear. 



Now here is a nice little problem for you to solve and 

 I want you to solve it to your own satisfaction, and when 

 you do, you will thoroughly understand it, and to under- 

 stand it is to never allow it to get you into trouble. We 



