9 6 



SCIENCE OF SUCCESSFUL THRESHING. 



openings stopped by carefully fitted pieces of wood, in 

 order to prevent sand and other gritty substances from enter- 

 ing the cannon bearings. 



Greasing the Gearing. The gearing should be kept well 

 coated with axle grease. It is true that many men argue 



FIG. 30. CUT SHOWING CANNON BEARINGS AND GEARING. 



that grease collects and holds sand which will cause cutting 

 of gears. To prove the fallacy of this belief, however, it is 

 only necessary to observe the gearing on engines which have 

 been run by men of this opinion. In many cases, the gearing 

 will be found more badly worn than its use would warrant, 

 The Friction Clutch. The friction clutch is used to con- 

 nect the engine to the traction gearing and wheels. By 

 means of it, the engine may be made to travel as slowly as 

 desired, while the engine proper is running at full speed. 

 When the clutch is in partial engagement, the shoes, (A), 



