THE INTERNAL - COMBUSTION TRACTOR 97 



thus avoiding any tension upon the clutch lever. The external 

 type, gripping the outside circumference of a wheel, is also 

 used, as well as planes gripping both sides of a revolving disk. 

 In place of an internal shoe, an expanding ring is employed 

 by some, also a cone, which is forced into a similarly shaped 

 ring. Several disks tightly pressed together, as in the multiple 

 disk clutch of an automobile, are also employed. 



BAND-WHEEL 



Without notable exception, all tractors are provided with a 

 band-wheel, or belt-pulley for transmitting power in stationary 

 work. This is most often placed upon one end of the crank- 

 shaft, where it acts as a second flywheel, but in a number of 

 high-speed engines it is placed upon a countershaft which re- 

 volves at a lower speed. As in steam engines, the band-wheel 

 is frequently made part of the transmission system, a single 

 clutch driving the band-wheel, which may drive either the belt 

 or traction gearing. Suitable provision is made to throw the 

 traction parts out of gear when work is to be done by the belt. 



GEAR DRIVE 



Where the crankshaft lies crosswise of the frame, the power 

 is usually taken directly to the drive- wheels by a train of spur 

 gears i. e., cylinders with parallel teeth cut or cast on the 

 circumference. Chains or friction wheels may replace part 

 of these gears. A large gear on the countershaft receives power 

 from the crankshaft and transmits it through a smaller gear on 

 the same shaft to the master gear, which drives the traction 

 wheel. When cylinders are mounted lengthwise of the frame, 

 it is necessary to change the direction of rotation to one which 

 will drive the tractor forward. This is accomplished by means 

 of bevel gears in addition to the ordinary set. 



The gears may be either of steel or semi-steel, the latter 

 being a mixture of steel and cast iron. The crankshaft pinion 

 and the gear it engages are usually of cast steel with machine- 



