TM-9-2815-200-35
ENGINE, WITH CONTAINER:TURBOSUPERCHARGED, DIESEL ,FUEL INJECTION ,90-DEGREE “V” TYPE, AIR - COOLED ,12 - CYLINDER , ASSEMBLY ;MODELS AVDS-1790-2M (2815-856-4996), AVDS-1790-2A AND AVDS-1790-2AM (2815-856-9005)
TECHNICAL MANUAL; DIRECT SUPPORT, GENERAL SUPPORT AND DEPOT MAINTENANCE MANUAL INCLUDING REPAIR PARTS AND SPECIAL TOOLS LISTS
TM-9-2815-200-35 - Page 46 of 779
1-12. Crankshaft, Flywheel, and Damper
Note.
The key letters shown below in
parentheses refer to figure 1-8.
a.
Crankshaft assembly (QQ) is a nitrided steel
forging with seven main bearing journals and six
crankpins. Each crankpin accommodates two
opposing
connecting
rod
assemblies (UU ).
Flanges are provided on the crankshaft for
mounting the flywheel (N ) on the rear end and a
torsional vibration damper (TT ) on the front
end.
b.
All crankpin and main bearing journals are
hollow to reduce weight. Holes are drilled
diagonally through each main bearing journal
and extend through the crank cheek and crank-
pin to provide a direct passage for oil under
pressure to the connecting rod and crankshaft
main bearings as shown in figure 1-9.
c. The crankshaft and flywheel are statically
and dynamically balanced.
d.
The torsional vibration damper (TT) is a
precision viscous type and is replaceable only as
an assembly.
1-13. Connecting Rods and Bearings
The connecting rod assemblies (UU, fig. 1-8)
are tapered, I-beam section steel forgings. A
bronze-lined, steel-backed, split, bushing type
bearing is pressed into the piston pin end of the
rod. The replaceable precision connecting rod
bearings are the steel-backed, split type having
copper-lead alloy bearing surfaces.
1-14. Pistons, Pins and Rings
The pistons (VV, fig. 1-8) are aluminum
forgings, cam ground and tapered to provide an
accurate fit in the cylinders at operating tern.
peratures. The piston dome is machined to the
shape of a conical section (toridal shape) so that
it tapers into the open type combustion chamber.
Each piston is fitted with four rings. The upper
three rings are compression rings and the bottom
ring is an oil control ring. The heavy walled,
tubular, steel piston pins are full-floating in the
piston and the connecting rod. Domed
aluminum plugs are inserted into each end of the
piston pin to center it in the piston and prevent
scoring of the cylinder wall.
1-15. Cylinders and Valves
Note.
The key letters shown below in
parentheses refer to figure 1-8 except where
otherwise indicated.
a.
Each cylinder assembly (fig. 1-1) is an
individually replaceable unit that consists of a
barrel, cooling fin muff, and a cylinder head.
The cooling fin muff is cast directly on the steel
barrel. The finned, cast aluminum cylinder head
is threaded and shrunk on the barrel. Cooling
fins, exhaust and intake ports, and a single
rocker box are cast integrally with the cylinder
head. Valve guides and seats are shrunk into
place in the head, The cylinder barrel is
“choked” at the head end to provide a straight
bore under running conditions. A mounting
flange is machined on the cylinder barrel near
the base to provide an attachment of the cylinder
to the crankcase. The cylinder assembly is
secured to the crankcase with studs and nuts. An
outer extension of the cylinder head encloses a
recess or rocker box, which houses the valves,
valve springs, and related parts. Rocker arm
assemblies (A and B ) are held in place by rocker
shafts in the cylinder head valve rocker support
cover.
b.
A camshaft bearing surface is provided in
each cylinder. The camshaft bearing is bored
with the cylinder head valve rocker support
cover in place.
Therefore the covers are not
interchangeable and each must remain as a part
of a specific cylinder assembly. Identifying
numbers are used on cylinder and covers to
prevent mismatching. Counterbores in the
rocker box. and rocker support covers ac-
commodate the intercylinder rubber hoses and
the steel flanges which enclose the camshaft
between the cylinders.
c.
The stem of the intake valve (YY) and
exhaust valve (XX ), for each cylinder, extends
into the rocker box. Three nested springs,
compressed between two retainers and secured to
the valve stem by two cone-shaped locks, hold
each valve to its seat. Each exhaust valve has a
positive valve rotator which also serves as the
lower spring retainer. Valve clearance adjusting
screws with flat swivel pusher pads are mounted
on one end of the valve rocker arms (A and B).
1-6
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