Doosan G643, Руководство по обслуживанию

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G643 (E) Service Manual Chapter 3. Engine Mechanical System 45
Engine Construction
The 4.3L (262 CID) engine is a liquid-cooled 90 V6
type with overhead valves, cast-iron block, cylinder
heads, and cast-iron balance shaft.
Cylinder Block
The cylinder block has 6 cylinders arranged in a “V”
shape with 3 cylinders in each bank. Starting at the
front of the engine, cylinders in the right bank are
numbered 1-3-5 and cylinders in the left bank are
numbered 2-4-6 (when viewed from the front of the
engine). The firing order of the cylinders is 1-6-5-4-
3-2. The cylinders are encircled by coolant jackets.
Cylinder Heads
The cylinder heads have one intake and one
exhaust valve for each cylinder. A spark plug is
located between the valves in the side of the
cylinder head. The valve guides are integral and the
rocker arms are retained on individual threaded
studs.
Crankshaft
The crankshaft is supported by four crankshaft
bearings. The number four bearing at the rear of the
engine is the end thrust bearing. The bearings are
retained by bearing caps that are machined with the
block for proper alignment and clearances.
Camshaft
The camshaft is supported by four full round, sleeve-
type bearings. A sprocket on the crankshaft drives a
timing chain which in turn drives the camshaft
through a sprocket.
Pistons and Connecting Rods
The pistons are made of cast aluminum alloy using
two compression rings and one oil control ring.
Piston pins are offset 0.9 mm (0.0354 in.) toward the
major thrust side (right side) to reduce piston slap as
the connecting rod travels from one side of the
piston to the other side after a stroke. The pins are a
press fit in the connecting rod and a floating fit in the
piston.
Balance Shaft
A cast-iron balance shaft is mounted in the
crankcase above and in line with the camshaft.
A camshaft gear drives the gear attached to the
balance shaft. The front end of the balance shaft is
supported by a ball-type bearing. The rear end of
the bearing uses a sleeve-type bearing.
Valve Train
The valve train is a ball pivot type. Motion is
transmitted from the camshaft through the valve
lifter and valve pushrod to the rocker arm. The valve
rocker arm pivots on its ball and transmits the
camshaft motion to the valve.
The valve lifters with roller followers keep all parts of
the valve train in constant contact. Each lifter acts as
an automatic adjuster and maintains zero lash in the
valve train and eliminates the need for periodic valve
adjustment.
Statement On Cleanliness And Care
An engine is a combination of many machined,
honed, polished, and lapped surfaces with very fine
tolerances.
Whenever valve train components, cylinder head,
cylinder, crankshaft, or connecting rod components
are removed for service, they should be retained in
order. At the time of installation, they should be
installed in the same locations and with the same
mating surfaces as when removed.
Any time the air cleaner or TBI unit is removed, the
intake opening must be covered. This will protect
against the entrance of foreign material which could
follow the intake passage into the cylinder and
cause extensive damage when the engine is started.
When any internal engine parts are serviced, care
and cleanliness are important. A liberal coating of
engine oil should be applied to friction areas during
assembly to protect and lubricate the surfaces on
initial operation. Throughout this Section, it should
be understood that proper cleaning and protection of
machined surfaces and friction areas is part of the
repair procedure. This is considered standard shop
practice even if not specifically stated.