wire. The action of the
spring keeps the breaker arm and the electrode in constant contact until
the push rod on the end of the piston strikes the arm and separates the
two parts. Breaking contact then produces the ignition spark. Since the
mechanism would spark at the end of both the exhaust and compression
strokes, the battery current is conserved by a contact strip, on the
underside of the larger exhaust-valve gear, by means of which the flow
of current is cut off during the greater part of the cycle.

On the left side of the combustion chamber is bolted the housing
containing the tiny intake valve. A comparatively weak spring seats this
valve in order that the suction created by the piston can easily pull it
open. Clamped onto the valve housing is the intake pipe, enclosing the
choke and carrying the carburetor on its forward side. The choke
consists of two discs which block the pipe, each with four holes at the
edges and one in the center. Turning one disc by means of a small handle
outside, so that the four outer holes cannot coincide with those in the
other disc, decreases the flow of air and causes all air to rush through
the center hole, where the tiny carburetor tube passes through. The
present carburetor was transferred over from the first engine. When
Frank later installed the engine on the carriage he noticed the close
proximity of the intake pipe to the open end of the muffler. Believing
that the fumes might choke the engine, he attached a long sheet-metal
tube to the intake pipe so that fresh air would be drawn in from a point
farther forward on the vehicle.

Moving to the right side of the engine brings the exhaust-valve assembly
into view. This valve is contained in a casting bolted over the exhaust
port in the side of the cylinder, and from the casting a pipe leads to
the muffler underneath. The valve is pushed open by a rod connected to a
crank which is pinned to the lower end of a shaft carrying an iron gear
on top. This gear is in mesh with a fiber gear, keyed to the upper end
of the crankshaft, with half the number of teeth. This ratio permits the
opening of the exhaust valve on every other revolution.

The crankshaft of the first engine was retained for the new engine, thus
giving the two engines the same stroke of 5-3/8 inches, but the bore was
increased slightly to 4-3/8 inches. With this larger bore and with the
engine speed increased to 500 rpm, Frank rated this engine at 4 hp.[19]
A heavie