212 STEAM ENGINES 



the piston-rod nut and the cylinder head; therefore, it cannot 

 back off very far before it will strike and break the cylinder 

 head. After the engine is stopped and the main stop-valve 

 is closed, the cylinder head should be taken off and the piston 

 nut set up as tightly as possible. As a measure of safety, 

 a taper split pin should in all cases be fitted through the piston 

 rod behind the nut or a setscrew should be fitted through the 

 nut. 



Slack Follower Plate. A slack follower plate or junk ring 

 will cause pounding in the cylinder. It seldom happens, how- 

 ever, that all the follower bolts back out at one time, but 

 it is not an infrequent occurrence that one of the follower 

 bolts works itself out altogether. This is a very dangerous 

 condition of affairs, especially in a horizontal engine. If the 

 bolts should get end on between the piston and cylinder 

 head, either the piston or the cylinder head is bound to be 

 broken. Therefore, if there is any intimation that a follower 

 bolt is adrift in the cylinder, the correct procedure is to shut 

 down the engine instantly, take off the cylinder head, remove 

 the old bolt, and put in one having a tighter fit. 



Broken Piston Packing. Broken packing rings and broken 

 piston springs will cause noise in the cylinder, but it is more of 

 a rattling than a pounding, and the sound will easily be recog- 

 nized by the practiced ear. There is not so much danger of 

 a breakdown from these causes as may be supposed, from 

 the fact that the broken pieces are confined within the space 

 between the follower plate and the piston flange. 



Piston Striking Heads. Pounding in the cylinders of old 

 engines is often produced by the striking of the piston against 

 one or the other cylinder head. One of the causes of this 

 is the wearing away of the connecting-rod brasses. Keying 

 up the brasses from time to time has the effect of lengthening 

 or shortening the connecting-rod, depending on the design, 

 and this change in length destroys the clearance at one end 

 of the cylinder by an equal amount. The remedy is to restore 

 the rod to its original length by placing sheet-metal liners 

 behind the brasses; this obviously will move the piston back 

 or ahead and restore the clearance. A rather rare case of the 

 piston striking the cylinder head is due to unscrewing of the 



