What makes an engine knock or pound? A loose pillow block box is a good
"knocker." The pillow block is a box next crank or disc wheel. This box
is usually fitted with set bolts and jam nuts. You must also be careful
not to set this up too tight, remembering always that a box when too
tight begins to heat and this expands the journal, causing greater
friction. A slight turn of a set bolt one way or the other may be
sufficient to cool a box that may be running hot, or to heat one that
may be running cool. A hot box from neglect of oiling can be cooled by
supplying oil, provided it has not already commenced to cut. If it
shows any sign of cutting, the only safe way is to remove the box and
clean it thoroughly.
Loose eccentric yokes will make a knock in an engine, and it may appear
to be in the wrist. You will find packing between the two halves of the
yoke. Take out a thin sheet of this packing, but don't take out too
much, as you are liable then to get them too tight and they may stick
and cause your eccentrics to slip. We will have more to say about the
slipping of the eccentrics.
The piston rod loose in cross-head will make a knock, which also appears
in the wrist, but it is not there. Tighten the piston and you will stop
it. The piston rod may be keyed in cross head, or it may be held in
place by a nut. The key is less liable to get loose, but should it work
loose a few times it may be necessary to replace it with a new one. And
this is one of the things that cause a bad break when it works out or
gets loose. If it gets loose it may not come out, but it will not stand
the strain very long in this condition, and will break, allowing the
piston to come out of cross head, and you are certain to knock out one
cylinder head and possibly both of them. The nut will do the same thing
if allowed to come off. So this is one of the connections that will
claim your attention once in a while, but if you train your ear to
detect any unusual noise you will discover it as soon as it gives the
least in either key or nut.
The cross-head loose in the guides will make it knock. If the
cross-head is not provided for taking up this wear, you can take off the
guides and file them enough to allow them to come up to the cross-head,
but it is much better to have them planed off, which insures the guides
coming up square against the cross-head and thus prevent any heating or
cutting.
A loose fly-wheel will most likely puzzle you more than anything else to
find the knock. So remember this. The wheel may apparently be tight,
but should the key be the least bit narrow for the groove in shaft, it
will make your engine bump very similar to that caused by too much or
too little "lead."