STEAM ENGINES 399 



a perfectly round hole with a pin fitting it just close 

 enough to allow a film of oil between the hole and the 

 pin. The closer a bearing can be made to conform to 

 this the better. 



As a bearing wears, a thick liner should be taken out 

 and a thinner one inserted. Never take out a thick liner 

 and then only partly draw up the boxes. This makes a 

 loose bearing and will cause trouble. 



550. Lubrication. Since the cylinder of the engine is 

 always hot when running, oil is required which will 

 stand higher temperatures than the oils for bearings. 

 This oil is generally known as cylinder oil. As a rule, 

 it is a heavier and blacker oil than is generally used for 

 lubrication. It is of such a nature that it will stand the 

 heat in the steam chest and the cylinder. Ordinary lubri- 

 cating oil would be decomposed by the heat. The oil 

 used for bearings, such as crank, eccentric, wrist pin, etc., 

 is of a lighter nature and is a good grade of common 

 lubricating oil. A new engine requires more oil than an 

 old one, and a cylinder when priming or foaming requires 

 more oil than when running regularly. The amount of 

 oil to use can be determined only by experience ; it is 

 better to get too much than not enough. A good method 

 of determining the amount of oil for the cylinder is to 

 keep track for a minute of the number of drops which 

 pass through the lubricator; then take the cylinder head 

 off and see if the walls are bright and shiny and feel 

 oily ; if so, the cylinder is getting enough oil. For bear- 

 ings and other places, the number of drops a minute 

 should be determined, and then the bearings watched 

 to see if they heat and if there is an excess of oil run- 

 ning off. 



551. Lubricators. Owing to the pressure in the steam 

 chest of an engine, some device has to be employed which 



