FARM MOTORS 393 



shoes used are made of wood, and are forced out against the 

 rim of the fly wheel by suitable linkage. 



The Differential. In order to permit the tractor to turn 

 corners, or change direction a mechanism must be introduced 

 which will allow one traction wheel to travel faster than the 

 other. This mechanism is called the differential. There are 

 two types of differentials, the bevel gear and the planetary. 



The Gearing. The gearing of a steam tractor is an 

 important part of the outfit, especially when the tractor is 

 used for traction purposes. It is now customary to make 

 the gears very ample in size and of material which will resist 

 wear to the greatest extent and still be capable of resisting 

 the shocks which must necessarily come upon them. Further- 

 more, the tractor should be provided with means of excluding 

 dust and grit from the gears, and with a system of lubrication 

 that will at all times keep the gears amply lubricated. 



QUESTIONS 



1. Discuss the different types of boiler mounting. 



2. Explain two ways of mounting the engine. 



3. In what two ways may large tractors be steered by power? 



4. What are some of the important features in the construction of 

 the traction wheels? 



5. What is the purpose of the cleats on the drive wheels? 



6. How is the power capacity of a steam tractor designated? 



7. How is a steam tractor controlled? 



8. What is the purpose of the differential gearing? 



9. Why is the gearing of a steam tractor worthy of careful atten- 

 tion? 



LIST OF REFERENCES 



Instructions for Traction and Stationary Engineers, William Boss. 

 Farm Engines and How to Run Them, James H. Stephenson. 

 Farm Machinery and Farm Motors, J. B. Davidson and L. W. 

 Chase. 



