76 ROUGH-AND-TUMBLE ENGINEER I 



but as we have said, the tapering key brings this half up 

 to its place. 



Now we think we have made this clear enough and we 

 will leave this and go back to the key again. You must 

 remember that we stated that the key was tapering or a 

 wedged shape. Since a wedge is equally as powerful as a 

 screw you must bear in mind that a slight tap will bring 

 these two boxes up tight against the wrist pin. Young 

 engineers experience more trouble with this box than with 

 any other part of the engine, and all because they do not 

 know how to manage it. You should be very careful no* 

 to get your box too tight, and don't imagine that every 

 time there is a little knock about your engine you can 

 stop it by driving the key down a little more. This is a 

 great mistake that many, and even old engineers make. 

 I at one time saw a wrist pin and boxes ruined by the 

 engineering trying to stop a knock that came from a loose 

 fly-wheel. It is a fact, and one that has never been satis- 

 factorily explained, that a knock coming from almost 

 any part of an engine will appear to be in the wrist. So 

 bear this in mind and don't allow yourself to be deceived 

 in this way, and never try to stop a knock until you have 

 first located the trouble beyond a doubt. 



When it becomes necessary to key up your brasses, 

 you will find it a good safe way to loosen up the set screw 

 which holds the key, then drive it down till you are satis- 

 fied you have it tight. Then drive it back again and 



