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4. CONNECTING RODS
Connecting rods are of conventional split bearing
design and of heat-treated alloy steel forgings. The
split crankpin "big" end is fitted with two semi-
Circular, special alloy, precision bearing inserts. A
bronze bushing is pressed into the "small end" piston
pin boss.
In current production rods a split, one-
piece bushing replaces the former solid type. The
big end bearing cap has a squirt hole from which oil
sprays into the opposite cylinder.
Connecting rods
are selected sothat the variation in weight within any
engine is not over 1/4 ounce.
5. CRANKSHAFT CONSTRUCTION
The alloy steel, one piece, six-throw crankshaft
is supported by four main bearings with semi - circular
steel backed precision inserts which are easily re-
placed. The crankshaft is drilled for lightness and to
provide pressure lubrication to crankpins. The crank-
shaft end clearance is maintained by split bronze
thrust washers at each end of the front main bearing.
The rear washer, between the front crankcheek and
the bearing, takes forward thrust. Rearward thrust
is taken by the front washer from a flange on the shaft
which also acts as an oil slinger. C-145 and
0-300
crankshafts have a blade extending from each side of
the cheek between NoT s 1 and 2 crankpins for attach-
ment of dynamiC damper counterweights. Each blade
has two holes bored through and steel bushed. Slotted
counterweights fit over the blades and have holes bored
through and bushed to match those of the shaft. Bush-
ings are sized to produce the desired frequency.
Pins
are hardened and are retained endwise by steel plates
and Tru-Arc snap rings.
A notched blade and a pin
in the 5th order weight assure correct installation.
6. CRANKCASE AND OIL SUMP CONSTRUCTION
a. The crankcase is a two-piece heat-treatedalumi-
num alloy casting, bolted together at the vertical
lengthWise plane through the crank and camshaft sup-
ports.
Rigid transverse webs hold the four main
crankshaft bearings and the four camshaft journals.
A specially designed oil seal prevents oil leakage at
the nose end of the crankcase.
Large lifter guides
are formed in the crankcase in a plane below and
parallel to the cylinders. Oil galleries molded in the
castings provide pressure lubrication to the lifter
guides, camshaft and main bearings. Circumferential
stiffening ribs under the cylinder pads give additional
strength and stiffness to the cylinder bosses. One cast
aluminum alloy mounting bracket on each Side of the
case near the front and one on each side at the rear
provide four engine mount paints, in all. Opposite
brackets are joined by through bolts, and each is also
attached to the case by two studs. A Lord bUShing,
clamped in each bracket, admits a 7/16 in. mount
bolt.
Spreading of current production crankcase
halves is prevented by nine headless through bolts
located in the upper and lower sections of the crank-
shaft bearing bosses, and four headless through bolts
located in the lower part of the camshaft bearing
bosses. Hydraulic "0" rings installed in grooves of
tie bolts and the through stud near the case split pre-
vent oil leakage to the bolt ends.
b. The oil sump is an aluminum alloy casting which
forms a trough beneath the open bottom of the crank-
case.
It
is closed at the front end and open at the
rear. The sump is attached by crankcase studs and
sealed by a thick, reinforced gasket. Drain plugs are
installed in front of and behind the carburetor mount
pad in the sump floor.
From the carburetor pad the
intake air passage extends upward through the sump
and branches to each side in a tee, ending at the in-
take manifold mount flanges at the sides of the sump
casting. Manifold flange screw holes and screw holes
in the rear surface for crankcase cover attaching
screws have helical-coil thread inserts. The sump
capacityis 8 U. S. quarts. The oil gauge rod, extends
through a guide pressed into a hole in the crankcase
left side and into the sump. A grooved shoulder on
the gauge carries a hydraulic "0" ring to prevent oil
splashing out along the rod. A clip type lock ring fits
on the guide and retains the oil rod in place securely.
7. CRANKCASE COVER
The magnesium alloy crankcase cover casting at
the rear of the engine houses the oil pump, suction
and pressure oil screens pressure relief valve and all
gears.
Both oil screens are at the bottom of the
cover. The relief valve is at the right Side, and the
oil filler neck is pressed into a boss at the upper left
side. Studded mount pads are provided on the cover
rear surface for two magnetos, the starter, generator
and tachometer drive housing.
The crankcase cover
extends over the rear end of the oil sump.
It
is at-
tachedtothe sump by five screws and to the crankcase
by six studs, with a gasket in the jOint. The passage
from the pressure oil screen outlet is cored at the
rear of the sump, ending at the upper left rear corner,
where a crankcase hole into the left oil gallery re-
gisters with it.
8. VALVE OPERATING MECHANISM
a. General. Zero lash hydraulic tappets fit alumi-
num alloy guides machined in the crankcase and so
sealed as to positively prevent oil leakage. Tappets
are drilled in such a manner that an oil passage is
provided from the tappets to the push rods, which are
made of light steel tubing with pressed-in ball ends,
drilled, hardened and ground.
This provides an oil
passage the entire length of push rod to rocker arm
bearings where the oil under pressure lubricates
valve stems and guides. The rocker acts directly on
the valve stem through a specially designed "foot" so
constructed as to prevent side-thrust on the valve
stem.
Aluminum bronze intake valve seats, and
corrosion-resistant stainless steel exhaust seats,
provide maximum service life.
Scavenging of oil
from the rocker boxes is by gravity through the push
rod housing tubes.
b. Hydraulic Valve Lifters.
The lifters are com-
posed of only four parts which can be disassembled;
the cup, cylinder, piston and cam follower body. The
piston and cylinder are not interchangeable.
The
lifters are automatically adjusted to function properly
with valve lash ranging from .
030
inch to .
110
inch
between the valve stem end and rocker arm with the
lifter fully deflated.
Oil lines to tappets operate on
full engine pressure and are located in such a way that
they register with lifter when valves are open. Oil
under pressure from the lubricating system of the
engine is supplied to the hydraulic lifter through hole
(H) to supply chamber
(J).
(See figure 4. )
With face of lifter on the base circle of the cam
and the engine valve seated as shown in figure 4, the
light plunger spring (K) lifts the hydraulic plunger (C)
so that its outer end contacts push rod, taking up the
clearance at this point and all along the valve train,
giving zero lash. As the plunger (C) moves outward,
7
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