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
makes of engines differ to such an extent that it is impossible to give
any rule or any definite amount of lead for an engine. For instance, an
engine with a port six inches long and one-half inch wide would require
much less lead than one with a port four inches long and one inch wide.
Suppose I should say one-sixteenth of an inch was the proper lead. In
one engine you would have an opening one-sixteenth of an inch wide and
six inches long and in the other you would have one-sixteenth of an inch
wide and four inches long; so you can readily see that it is impossible
to give the amount of lead for an engine without knowing the piston
area, length of port, speed, etc.
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