he
eccentric gives to the valve its quickest movement, or between the
eccentric dead centers. The cut off eccentric is considerably ahead of
the main eccentric, and about even with the crank. If it was not for
the reversal of motion of the cut off valve through the rocker arm
this eccentric would be about in line with the crank, but on the other
end. The movement of the cut off valve, therefore, at the time of port
opening is very little, being about on its dead center, passing which,
it immediately commences to close.

The object of the peculiar construction of the rocker arm, and the
pivot for the cut off rocker being placed thereon, is to provide equal
travel on the back of the main valve, no matter what the cut off. I
have already explained, in connection with the slide valve, that
advancing the eccentric does not change the movement of the valve on
its seat, but simply its relation to the movement of the piston. You
will see that this is unchanged as using the main valve as a seat or
any other seat. If the main valve was to remain stationary, and only
the cut off valve to be operated by its eccentric, the movement of
this cut off valve on a certain plane would be the same for all
positions of the eccentric.

Moving the main slide does not affect the matter in any way, for it
moves at the same time the pivot of the cut off, and while the cut off
seat has assumed a different position with reference to the engine, it
is still as though stationary so far as the cut off valve is
concerned. This is the object of this peculiar construction, and not,
as some engineers suppose, simply to make an odd way of doing things.
And the object of it all is to give at all cut offs the same amount of
travel, so that there might be no unequal wear to bring about a leak,
to prevent which a perfect balancing has been sacrificed.

Referring to the valve and this engine as to how it will satisfy our
requirements of a perfect valve gear, we find that the first
requirement of a rapid and full opening is met, in that the opening
occurs when the main eccentric is moving very rapidly, yet not its
fastest, and while this opening will be very satisfactory, it is not
so rapid an opening as is obtained in some other forms of valves and
valve gears, but this could be overcome very readily by increasing the
lead a trifle, and in my experience with these engines I find that the
practice is very general by engineers and by builders themselves to
gi