STEAM ENGINES 211 



of the liners slipped out without the necessity of stripping the 

 journal. 



In some instances journal-boxes are fitted with keepers, or 

 chipping pieces, as they are sometimes called. These usually 

 consist of cast-brass liners from i to | in. in thickness, 

 having ribs or ridges cast on one side, for convenience of 

 chipping and filing. These keepers are sometimes made of 

 hardwood and are capable of being compressed slightly by the 

 pressure exerted upon them during the setting-up process. 

 When the boxes are babbitted, the body of the box is occasion- 

 ally made of cast iron, in which case iron liners and keepers 

 are used instead of brass ones. 



Loose Thrust Block. In engines fitted with some types of 

 friction couplings, there is a thrust exerted upon the shaft 

 in the direction of its length. This will necessitate having a 

 thrust bearing, or thrust block, as it is sometimes called. There 

 are a number of types of thrust bearings, but the most common 

 is the collar thrust, which consists of a series of collars on the 

 shaft that fit in corresponding depressions in the bearing. 

 If these collars do not fit in the depressions rather snugly, 

 the shaft will have end play and there probably will be more 

 or less pounding or backlash at every change of load on the 

 engine. This can be remedied only by putting in a new 

 thrust bearing and making a better fit with the shaft collars, 

 unless the rings in the bearing are adjustable, in which case 

 the end play may be taken up by adjusting the rings. 



Water in Cylinders. Pounding often occurs in the cylinders 

 and is frequently caused by water due to condensation or 

 carried over from the boilers. This may be a warning that 

 priming is likely to occur in the boilers or has already com- 

 menced. If the cylinders are not fitted with automatic relief 

 valves, the drain cocks should be opened as quickly as possible 

 and the throttle closed a little to check the priming. 



Loose Piston. Another source of pounding in the cylinder 

 is a piston loose on the rod; this will result if the piston-rod 

 nut or key backs off or the riveting becomes loose, permitting 

 the piston to play back and forth on the piston rod. If due 

 to backing off of the nut, the engine should be shut down 

 instantly. There is generally very little room to spare between 



