260 AGRICULTURAL ENGINEERING 



enough, these gears should be of liberal dimensions, especially 

 in width, to resist wear. It is an advantage to have the gears 

 so arranged that the thrust which exists between separate 

 pairs of gears shall balance as far as possible. 



Due provision should be made to keep the gears well 

 lubricated and well protected from dust. There is no good 

 reason why the gears of mowers should not be arranged to 

 run in oil, although this is not practiced. 



The small, fast-moving gear pinion is the first to wear 

 out, and the construction of the mower should be such as 

 to permit this pinion to be easily replaced. There is con- 

 siderable end thrust on the crank shaft upon which the bevel 

 gear pinion is placed, owing to the tendency for the gears to 

 force themselves apart. This end thrust should be carefully 

 provided for. Some of the best mowers upon the market 

 are made with a ball-thrust bearing. Other mowers have 

 hardened steel washers to take the wear, and in any case 

 there should be means of adjusting for wear. 



The chain drive mower is used to some extent at the pres- 

 ent time, but not as much as formerly. There are at least 

 two disadvantages of the chain-drive mower, in which one 

 pair of gears is replaced by a pair of sprokets and a chain or 

 link belt; first, it is not as positive in action as the gears; and, 

 second, the chains do not seem to be as durable as the gears. 



Usually mowers have but two pairs of gears, but some 

 mowers have three. No serious objections can be made to 

 the latter. At least one make has two speeds for the knife, 

 obtained by changing gears. The lower crank end of the 

 crank shaft should have a bearing which will permit adjust- 

 ment for wear. One of the most common methods of mak- 

 ing this adjustment is to rep 1 ace an interchangeable brass 

 bush used as the bearing lining. In mowers there is an 

 adjustable cap to the bearing, which may be adjusted by 



