92 POWER AND THE PLOW 



In both the steam and the gas engine cylinder, there is dan- 

 ger of feeding too much oil and creating a heavy deposit. This 

 will act as a collector of the scale-forming material which comes 

 over in the priming of the steam boiler, and the grit which 

 comes through the air intake pipe on the gas engine. The 

 paste thus formed is ideally adapted to cutting and scoring 

 the cylinder, just as emery paste will remain longer between 

 two metal surfaces than dry emery powder. As one of the 

 leading lubrication experts, Mr. F. M. Williamson, put it: 

 "You see the danger of assuming that if a little oil is good, 

 more is better." A number of special gas engine oils of 

 excellent quality are put out by the oil companies, and in 

 justice to the tractor a good brand should be used, and used 

 judiciously. 



COOLING SYSTEMS 



The exhaust will carry from 35 to 40 per cent, of the total 

 heat generated in the gas engine. Since only from four to 

 five per cent, will be consumed in friction of the piston and 

 bearings, and, as a rule, not more than 20 to 25 per cent, will 

 be delivered as useful work, it follows that the cooling system 

 must remove at least one third of the heat. The cylinder is 

 cooled in order to make it possible for the operator to work in 

 comfort; to prevent damage to the cylinder and valves, since 

 cast iron melts at a lower temperature than is frequently 

 realized at the moment of explosion; to prevent burning the 

 lubricating oil before it completes its work; to avoid igniting 

 the incoming charge by the heat of the cylinder walls; and in 

 order to allow a higher compression pressure, which in turn 

 gives a greater amount of power for a given size of cylinder 

 and a given quantity of fuel. 



A number of systems which are feasible in stationary work 

 are unsuitable for tractors. In the case of the self-contained 

 portable motor, the quantity of cooling medium which can be 

 transported is necessarily limited and the unusually rough, 



