THE INTERNAL -COMBUSTION TRACTOR 91 



In the gravity system small sight-feed oil cups are placed at 

 convenient points, and the amount of oil delivered is governed 

 by the size of the opening from the cups. On a small horizontal 

 engine this method is quite satisfactory, more so than on up- 

 right engines unless oil cups are placed on either side of the 

 vertical cylinder. Owing to the severe conditions which the 

 tractor must meet, a more positive system is necessitated. 

 The force-feed system consists of a mechanically operated 

 lubricator with a number of separate pumps capable of deliver- 

 ing oil against considerable pressure. This is commonly used 

 to supply oil to the cylinder and to the camshaft and crank- 

 shaft bearings. The drip from these sources is usually col- 

 lected in the crankcase where a considerable quantity is allowed 

 to accumulate. At a certain level this oil will be dipped by 

 the rapidly revolving crankshaft, and a spray will be sent into 

 the cylinder and every part of the crankcase. This is called 

 the splash system, and on some engines it is depended en- 

 tirely upon for lubricating the cylinder. However, the heat 

 will evaporate some of the lighter parts of the oil and in the 

 course of time it becomes heavy and dirty. The splash, there- 

 fore, is used most successfully in connection with a force-feed 

 lubricator, which is constantly bringing fresh oil, while an over- 

 flow drains off a certain quantity from the crankcase to the 

 gears below. 



The lubrication of bearings on gas tractors presents no new 

 problems, but the lubrication of the cylinder is vastly different 

 from that of the steam cylinder. In the latter the effort is 

 made to procure an oil which will emulsify and cling as a thin 

 film to the cylinder wall, resisting the high temperature for 

 a considerable length of time. In the gas engine the oil must 

 do its work in the face of so high a temperature as to make it 

 impossible for the oil not to be broken up. As a result, part of 

 any oil will be burned, and the best gas engine oil is one that, 

 after performing its duty, will mix with the charge and be 

 burned completely. 



