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."

LEAD

What is lead? Lead is space or opening of port on steam end of
cylinder, when engine is on dead center. (Dead center is the two points
of disc or crank wheel at which the crank pin is in direct line with
piston and at which no amount of steam will start the engine.) Different