KNOCKS OR POUNDS.
The Knocks or Pounds of steam engines are frequently caused by lost motion in the crank and wrist-pin boxes, valve rod and valve, cross-head and link; looseness of the piston rod, pillow block or main bearings, follower plate, or eccentrics; the slide valve having not enough or too much lead, the exhaust being cut off too soon or too late, shoulders being worn in each end of the cylinder by the packing rings not traveling over the counter-bore at the end of each stroke; or shoulders may be worn in the guides by the cross-head slides, or they may not be adjusted properly to fit the guides; boiler may foam, causing the water to be drawn over in cylinder; the piston rings may leak, thus causing cushioning; and as the crank approaches the centers, steam occupies the space between the cylinder head and piston, causing a tremendous strain upon the engine; the piston rod being packed too tight, the boxes and pins being worn flat or oval; the key in driving pulley may be loose.
TO REMEDY KNOCKS OR POUNDS
OF A STEAM ENGINE.
While it is hardly possible to prescribe a remedy for all cases, if the following practical methods are closely followed they will be found to be very useful, although in many instances the remedy must be determined by the circumstances of the individual case.
The knock or pound of boxes in connecting rod at cross-head or crank pin or the valve rod, may be remedied by taking out the boxes, and filing off the top and bottom inside edges sufficiently to allow them to just come together and not fit the pin too tightly. In replacing them, be careful not to key them up too tight.
Where there is not sufficient draught in the key or gib, place a liner in front or behind the boxes.
Knocks or pounds in the link may be remedied (if the link block has too much play in the link) by reducing the liners in each end of the link enough to fit the block properly.
The knocks or pounds of piston are caused by the rod becoming loose in the head; and if allowed to continue, will destroy the fit of the rod in the hole. It may be remedied under such circumstances by removing the rod, re-boring the hole and bushing it perfectly true, and refitting the rod.
Knocks or pounds of follower plate are generally caused by dirt accumulating in the hole, which will not allow the bolts to enter far enough to take up the lost motion of the plate, or the bolts may be too long. To remedy this, remove the accumulation of dirt from the hole, or shorten the bolts.
The knocks or pounds in main crank shaft, if caused by the bearings being worn oval or out of round, may be remedied by removing the shaft; true it up in a lathe, and refit or re-babbitt the boxes.
The knock or pound in eccentrics is generally caused by the eccentric straps being too loose upon the eccentrics, which can be remedied by reducing the liners in the straps to allow them to fit perfectly.
The knock or pound in slide valve caused by being improperly set, may be remedied by taking off the steam chest bonnet and re-adjusting the valve so as to give the same amount of lead at each end of stroke. This being done, and the valve well proportioned and the connections properly fitted, there should be no knocks or pounds from this cause.
The knock or pound in cylinder caused by shoulders being worn in it, can be remedied by re-boring the cylinder, being sure to make the counter bore of sufficient depth to allow the piston rings to overlap them at the end of each stroke.
The knock or pound on guides caused by shoulders being worn on them, is remedied by planing the guides and making the shoe slides of sufficient length to overlap the guides at either end when crank is on the center.
The knock or pound caused by the cross-head slides not fitting the guides properly, may be remedied by adjusting them both top and bottom to fit the guides closely, being careful not to get them too tight, which causes undue wear and strain upon the frame.
The knock or pound caused by wrist-pin or crank-pin becoming worn flat or oval, may be remedied by filing them perfectly round.
The knock or pound caused by the piston leaking, which causes cushioning, can be remedied only by having a tight piston.
The knock or pound caused by the driving pulley key being loose, can be remedied by driving the key in its seat; or if a defective key, replace by a new one perfectly fitted.
If the knocks or pounds are caused by lost motion in any of the revolving, reciprocating or vibrating parts of an engine, they may be detected and located by placing the finger upon the different parts while the engine is running very slowly or worked back and forth by hand.