The first pilot was planned, 1832, by Robert L. Stevens. A frame made
of oak, eight by four feet, pinned together at the corners, was made.
Under one end of it a pair of wheels twenty-six inches in diameter
were placed in boxes, and the other end was fastened to an extension
of the axle outside of the forward driving wheels, it having been
found by experience that a play of about one inch on each side on the
pedestals of the front wheels of the pilot or engine was necessary in
order to get around the curves then in the tracks. For years afterward
there was very little change in constructing the pilots from that
originally applied to the "John Bull."
The spiral spring, which held the front wheels of the pilot in place,
acted substantially as the center pin of a truck. The turntables in
use on the road were so short that it was necessary to unconnect and
take off these pilots before turning the engine. After the pilot was
adopted the forward large wheel on right of the engine was made loose
on the shaft in order to afford additional play in going around
curves. Other[6] changes and additions were also made in the
locomotive.
[Footnote 6: Changes in the locomotive "John Bull" since date of
construction, 1830:
Steam dome changed from rear of boiler forward to a part over what
was called the "man-hole," and throttle valve placed therein.
Steam pipes changed to outside of boiler, connecting new dome with
smoke box, entering it on each side.
In the beginning the reverse gear was changed from one single
eccentric rod on each side to two on each side, connecting on to
the same eccentric wheel, and the lifting rod, in pulling back,
lifted the forward gear hook off the rocker arm, and the back
motion hook then connecting on the rocker arm reversed the engine.
Side rods were never used.
Driver spring was changed from a bearing under the pedestal boxes
to a point over the boxes.
The pilot was attached in this manner:
Right forward wheel being loose, forward axle extended eight
inches beyond box on each side; to this was attached the beam of
the pilot, having play of about one inch between box and pedestal
plate to act while going around curves. The weight of forward part
of engine rested upon a cross brace of the two-wheel pilot, which
took bearing by a screw pin surrounded by a spring, by turning
which pin the weight on the drivers could be adjusted.
A brace used as a hand rail was added on top of the frame, bracing
frame and acting as a guide to the driving springs.
Water-cocks changed from right to left side of the boiler.
Bell, whistle and headlight were added.
Balance safety valve scale was changed forward to a point over
barrel of boiler, the secret valve being over the new dome.]