Smyrna times., 1929-06-19
CHEVROLET MOTOR COMPANY
James M.Crawford, Chief Engineer
Discusses Power of New Chevrolet


James M.Crawford, Chief Engineer
Discusses Power of New Chevrolet
In response to an unexpected
number of inquiries for an explain
alton Of the unusual power found in
the new Chevrolet six, James NJ.
Crawford, recently appointed chief
engineer of Chevrolet Motor Com
pany, discussed this subject with
technical editors last week. "The
abundance of power found in the
rev Chevrolet six is made possible
by its short stroke engine design,
which embodies an advanced meth
cd of COOLING" he said. "This con-
struction brings water around both
inlet and exhaust valve seats. 1t
differs radically from the Siamese
system of valve ports, and makes
for greater durability Of the -alve
train. In starting off any new en-
gine design, one Of the early con-
siderations is how long shall the
motor be in order to lay out the
chassis into which it must fit. On
account of the Importance of wheel
base, it is desirable to keep the mo-
tor length down to a minimum.
This is one of the conditions which
has brought the small bore, long
stroke, high speed engine into the
picture Durability being one of
our first requirements, we did not
feel that we should shorten the en-
CINE to meet a certain wheel base.
We chose, rather, to design motor
of the short stroke and medium
bore type. In order to insure round
cylinders, we decided to circulate
water completely around all the
bores. Therefore, after the bore
was determined the cylinder length
was automatically governed by the
bore size, and the bore size was de-
termined after taking the stand
that short stroke, low speed en-
CINE was the only way we could in
sure durability. This is quite the
contrary to the way most engines
are laid down, where cost is an i'm
portant consideration. Generally,
the designer shortens the motor by
increasing the stroke and reducing
the bore. In this case the length
of the cylinder block is then deter
mined by the valve area rather
than the piston head area. On ac-
count of this limitation, in taking
advantage of the small bore and
keeping the cylinder block as short
as possible, the water is invariably
taken from between the valve ports
at least between the inlet and eX-
Eaust valves. Racing experience
and dynamometer test work, where
high engine output is maintained
continuously have definitely proved
that a compromise in this direction
is responsible for a falling off in
horse power on account of valve
warpage caused by uneven temper
ature at the valve seats. In the
Chevrolet six design there has been
plenty of room allowed for water
completely around all the valves,
both on account of the piston diam
eter and the fact that the valves
are comparatively small. A large
diameter is not necessary on ac-
count of the comparatively low
maximum speed of the engine. In
addition to the value of well cooled
valve seats, it is important that the
proper valve clearance be main
tanned at all times. In this respect
the overhead design is at consid-
cradle advantage compared to the
LrHead construction in that the adj
justment for the valve clearance is
much more assessible. In the or
dinary side valve design, it is nee
essary to remove several plates to
get at the valve adjustment. In
variably the valves are located in
an inaccessible place and special
wrenches, together with a great
deal of care, are necessary when
making adjustments. In the over
head design, it is only necessary to
remove a single cover and the valve
= 7 11,