IMPORTANCE OF THE PISTON IN THE TRAIN OF MECHANISM.
The piston is an autocratic member of the machine. For thousands of miles it toils to push the engine ahead, every thing going smoothly so long as it is confined to its recurring journey; but let any attachment break, or a key fly out that will increase the piston’s travel, and away the piston goes, right through a cylinder-head.
CAUSES THAT LEAD TO BROKEN CYLINDER-HEADS.
The causes which most commonly lead the piston to smash out cylinder-heads, are broken cross-heads, broken piston-rods, and broken main-rods. A main crank-pin or wrist-pin breaking, is almost certain to leave one end of the cylinder a wreck. These may be termed the major causes for breaking out cylinder-heads; but there are numerous minor causes, which are scarcely less destructive. A piston-rod key begins to work loose. It is hammered down occasionally, which does not improve its fit; and some day it jumps out altogether, letting the piston go on a voyage of discovery. A machinist of the careless sort has been examining a piston’s packing, and, in screwing up the follower-bolts, one of them gets a twist too much. Drilling out a follower-bolt is a troublesome operation, so Mr. Careless lets it go. On the road this head drops out, and a broken cylinder-head is the consequence. One of the worst causes of breakage to a cylinder that I have ever seen, was caused by the packing-ring of the piston catching in the steam-passage. Part of the ring broke off, and wedged itself between the advancing piston and the cylinder. The wedge split the cylinder open, and the remainder of the piston acted like a pulverizer upon the fragment of the cylinder.
BROKEN CYLINDER-HEADS OFTEN PREVENTABLE.
The causes which eventually lead to broken cylinder-heads often originate from preventable strains. Thus, cross-heads are frequently fractured by main-rod connections pounding; and weaknesses, that ultimately bring crank-pins to disaster, originate in a similar way. A loose piston-key is liable to crack the piston-rod, if it does not give trouble by jumping out. Loose guides have a tendency to spring piston-rods, and throw unnecessary strain upon them. Pistons lined out of true, are dangerous for the same reason. A pump-plunger working out of line, or badly secured in the lug, throws a distressing load upon the cross-head. And so the list of potential accidents grows. Like the steady water-drop that wears into the adamantine rock, trifling defects, assisted by time’s action, prove stronger than the most massive machine.
When any thing happens to permit the piston to break out a cylinder-head, the engine can be put in running trim by taking off the valve-rod and main-rod, and setting the valve on the center of the valve-seat. Blocking the cross-head is unnecessary, if the break will allow the escaping steam to pass through; for then no further tension can be put upon the piston to cause further damage. If, by an extraordinary freak of good luck, a piston-rod breaks without causing other damage, the cylinder-head must be taken off, and the piston removed. Then cover the ports, and take down the main-rod on that side. Or, if the cross-head is all right, the main-rod may be left untouched. When the cross-head breaks, it generally entails taking out the piston, centering the valve, and taking down the main-rod on that side.
WHEN A MAIN-ROD BREAKS.
With a broken main-rod which does not knock out the cylinder-head, the main-rod and valve-rod should be taken down, the valve secured on the center of the seat, and the cross-head blocked with the piston at the back end of the cylinder.