218 STEAM ENGINES 



In removing the liners, great care should be exercised not 

 disturb the brasses any more than is absolutely necessary. 



Warped and Cracked Brasses. Warped and cracked brasses 

 will cause heating, because they do not bear evenly on the 

 journal, and hence the friction is not distributed evenly over 

 the entire surface. If the distortion is not too great, the 

 brasses may be refitted to the journal by chipping, filing, and 

 scraping; but if they are twisted so much that they cannot, 

 within reasonable limits, be refitted, nothing will do but new 

 brasses. 



Cut Brasses and Journals. Brasses and journals that have 

 been hot enough to be cut and grooved are liable to heat up 

 again any time on account of the roughness of the wearing 

 surfaces. As long as the grooves in the journal are parallel 

 and match the grooves in the brasses, the friction is not greatly 

 increased; but if a smooth journal is placed between brasses 

 that ara grooved and pressure is applied, the journal crushes 

 the grooves in the brasses and becomes brazed or coated with 

 brass, and then heating results. The way to prevent heating 

 from this cause is to work the grooves out of the journal and 

 brasses by filing and scraping as soon as possible after they 

 occur. 



Imperfectly Fitted Brasses. Faulty workmanship is a com- 

 mon cause of the heating of crankpins, wristpins, and bear- 

 ings. The brasses in that case do not bear fairly and squarely, 

 even though they appear all right to the eye. A crankpin 

 brass must fit squarely on the end of the connecting-rod and 

 the rod itself must be square. If the key, when driven, forces 

 the brasses to one side or the other and twists the strap on the 

 rod, it will draw the brasses slantwise on the pin and make 

 them bear harder on one side than on the other, thus reducing 

 the area of the bearing surfaces. The same is true of the shaft 

 bearings. If the brasses do not bed fairly on the bottom of 

 the pillow-block casting or do not go down evenly, without 

 springing in any way, heating will result. 



Edges of Brasses Pinching Journal. Brasses, when first 

 heated by abnormal friction, tend to expand along the surface 

 in contact with the journal; this would open the brass and 

 make the bore of larger diameter were it not prevented by the 



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