GAS ENGINES , 521 



LUBRICATION 



Selection of lubricant. The problem of gas-engine 

 lubrication is the selection of a lubricant which will stand 

 the high temperature of the cylinder wall and still maintain 

 a surface film. Although the explosion temperature may 

 approach 3000 , this drops rapidly, and it is generally agreed 

 that the oil film on the cylinder wall is seldom exposed to a 

 temperature higher than 700 . It does not follow that an 

 oil must stand a temperature of 700 before burning, for it 

 is exposed to this temperature for but a fraction of a second. 



Lubrication requirements. The lubrication requirements 

 of engines vary much more than is generally believed. When 

 an oil is found which reaches all parts and produces a mini- 

 mum of carbon in the cylinder, there is little use in trying 

 another oil. All oils produce some carbon. The physical 

 characteristics of a good gasoline engine oil for summer vise 



are: 



Specific gravity 28-30 Baume 



Viscosity 300-400 at 70 F. 



Viscosity 50-60 at 200 F. 



Fire point . • 350 ~450 



Cold point 1 5° above zero 



Free carbon 1 per cent or less 



Acid None 



For winter the cold point should be o° or lower. 



The method by which a lubricant is delivered to the sur- 

 faces is of prime importance to the engine user. All exterior 

 journals and bearings may be provided with lubricant by 

 oil pump, oil cup, ring oilers, chain oilers, wick oilers, 

 or frequent hand application. Inside the crank case of a 

 multiple-cylinder engine the problem of lubrication is handled 

 in one of two ways, or by a combination of the two. The 

 oldest and most commonly used is the splash system. In 

 this system a pocket of oil is placed so that the crank may 

 dip into it. The result is a splashing or throwing of the oil 

 over the whole interior surface of the crank case, including 

 the cylinder wall, when the piston is at the maximum ''in" 



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