390 AGRICULTURAL ENGINEERING 



mounted on brackets attached to the side of the boiler, the 

 boiler is said to be side-mounted. 



When an axle is provided for the traction wheels and it is 

 placed to the rear of the boiler, it is. said to be rear -mounted. 

 As it is quite impossible to keep the traction wheels in the 

 side-mounted engine perfectly true, the rear-mounted form 

 is generally recognized as being the more preferable of the two. 

 Any wear or spring at the outer ends of the axles will allow the 



Fig. 251. An undermounted double-cylinder steam tractor. 



wheels to approach each other at the top and to spread at the 

 bottom, thus throwing the gearing out of alignment. 



Some rear-mounted boilers have the main axle mounted 

 with radius arms, that the boiler may be carried on springs 

 and still permit the gearing to be in proper mesh at all times. 



The Mounting of the Engine. The usual method of 

 mounting the engine is to attach it to brackets or flanges 

 riveted to the top of the boiler proper. This construction is 

 generally referred to as top mounting. 



As previously mentioned, another type of construction 

 provides a frame sufficiently strong to carry the boiler and 



