Abilene weekly reflector. [volume] (Abilene, Kan.) 1888-1935, 1913-09-18

as possible to the point at which the flame is passed into
the compressed gas; in other words, as nearly as posi-
BILE to the points of the Spark plug. This can be done only
in a cylinder Of the Buick type of construction. As a
matter of fact, the distance from the points of the spark
plug to the farthest point in the combustion chamber In
the Buick motor is less than one-half that found in a CT"
head motor of equal size; and some of the manufacturers
of the latter type have even been forced to use two spark
plugs, one at each end of the combustion chamber, in or
der to secure the same results Buick obtains with it's
Overhead and single plug. The disadvantages of dou-
bling the number of spark plugs are too obvious to need
further mention. In the Il" type, as ordinarily con-
structed, the spread Of flame must pass through the gas
from the sparkling points across the cylinder and around
into the side pocket over the exhaust valve. This is ne
cessarily a slower process Of combustion, and there is a
corresponding loss of power.
Therefore, as the gas expansion depends upon the
rapidity OF flame propagation, or, as commonly called,
the explosion, it can be seen that the Overhead valve
motor possesses an important advantage over both other
types.
There are also additional advantages. Not only does
the explosion in an Overhead valve motor prove more
positive, but it cleans or scavenges, the cylinders Of
burned gas more completely on the exhaust stroke of the
piston, This is due to the fact that the exhaust stroke
forces the burned gas straight out through the exhaust
valve at the top OF the cylinder, and not from the cyln-
der through a pocket and thence out. In the pocket type
a certain part of the old gas remains after the exhaust
valve closes. The dead gas that stays in the pocket of
the motor cylinder is thus mixed with the fresh gas in
PRODUCED through the inlet valve on the next charge, re-
ducing it in amount and causing deterioration in quality.
No such condition is possible with the Overhead valve.
The fresh charge finds a perfectly clean cylinder. It
fills it to the fullest capacity with clean gas, and this nat
urally produces a greater expansion and a correspond
ingly greater piston pressure when fired. Ii
The absence of pockets or chambers in the straight
walled cylinders of the Overhead type makes possible
more accurate machining in their manufacture and in
sures a more symmetrical chamber for combustion. As
this chamber is merely the upper part of the cylinder, it
allows this full machining, whereas the pockets on other
types, from the very nature of their construction, can
not possibly be reached with any tool, and therefore can
not be m4Chlnn0 r SmaOfhnd ont From OnnaSSItv thnrn
must be certain places in these pockets where there are
small irregularities and where the wall is rough.
The smoother the surface, the less is the tendency to
carbonization. 1t naturally follows that these rough
places provide a greater opportunity for pre-ignition, due
to the overheating of deposits or projections, especially
when the motor is under heavy duty, or where full throt-
tie or high speed is required.
The fully %machined, smooth, straight cylinder of the
Overhead assures an absolutely consistent motor, as all
cylinder surfaces are exactly alike, and each cylinder will
handle its full charge in exactly the same way, under all
driving conditions. No irregularity or ~roughness can
exist In any part of it.