STEAM ENGINES 219 



cooler part near the outside and by the bedplate itself. If 

 the brass has become hot quickly and excessively, the resist- 

 ance to expansion produces a permanent set on the layers of 

 metal near the journal, so that on cooling, the brass closes and 

 grips the journal. This is why some bearings always run a 

 trifle warm and will not work cool. A continuance of heating 

 and cooling will set up a bending action at the middle of the 

 brass, which must eventually end in cracking it. Heating 

 produced in this way may be prevented by chipping off the 

 brasses at their edges parallel to the 

 journal, as shown at a in the accom- 

 panying illustration, in which b is -a 

 section of the journal and c and d 

 represent the top and bottom brasses, 

 respectively. 



Stopped Oil Feed. It does not take 

 long for a bearing to get very hot if it 

 is deprived of oil. The two principal 

 causes of dry bearings are an oil cup 

 that has stopped feeding, either by reason of being empty or 

 by being clogged up from dirt in the oil, and oil holes and 

 oil grooves stopped up with dirt and gum. 



Insufficient Oil. The effect produced upon a bearing by 

 an insufficient oil supply is similar to that of no oil, but in a 

 less degree. Of course, it will take longer for a bearing to heat 

 with insufficient oil than with none at all, and the engineer 

 has more time in which to discover and remedy the difficulty. 



Dirty and Gritty Oils. Oils that contain dirt and grit are 

 prolific sources of hot bearings. There is a great deal of dirt 

 in lubricating oils of the average quality; therefore, all oil 

 should be strained through a cloth or filtered, no matter how 

 clear it looks. All oil cups, oil cans, and oil tubes and channels 

 should be cleaned out frequently. Oil may be removed from 

 the cups by means of an oil syringe, and all oil removed from 

 the cups and cans should be strained or filtered before being 

 used. 



Oils of Poor Quality. There are on the market many 

 lubricating oils whose quality cannot be definitely decided 

 on without an actual trial, and it is a difficult matter to avoid 



