Section XV. CYLINDER HEAD AND VALVE OPERATING MECHANISM
a. The cylinder head is a one-piece alloy iron
casting and is secured to the upper part of the cylin-
der block by heat-treated capscrews. Inlet and outlet
ports are provide in the cylinder head for the intake
of air and the expulsion of exhaust gases. Cored
passages are provided for the circulation of coolant.
Located in the cylinder head above each cylinder is
an intake valve, valve guide, valve spring, spring
retainer and locks, an exhaust valve, valve guide,
valve spring, spring retainer and locks, a fuel injec-
tion nozzle, and two rocker arms. The top of the cyl-
inder head is enclosed with a cylinder head cover and
sealed with a gasket.
b. The rocker arm assembly, consisting of two
rocker arms for each cylinder, is mounted on a com-
mon rocker arm shaft supported by rocker arm shaft
brackets attached to the cylinder head. One rocker
arm actuates the Intake valve and the other actuates
the exhaust valve.
The camshaft rotates in bearings mounted inside
It is mechanically timed with the
crankshaft to open and close valves at proper intervals.
Valves are operated by caroming action produced by
lobes located along the length of the camshaft.
d. The push rods extend down through the cylinder
head, cylinder block, and into valve lifters which are
held in position by the camshaft. The upper end of the
push rods are concave to receive the ends of the valve
lash adjustment screws threaded into one end of the
rocker arms. The other end of the rocker arm actu-
ates the valve through the action of the push rod. When
the push rod is forced upward by the camshaft lobe, the
rocker arm is raised on one end and forced down on the
other end, opening the valve. The tension of the valve
spring closes the valve when the push rod moves down-
e. An oil hole through the cylinder head at the
flywheel end extends from the engine oil gallery. An oil
feed tube is connected from the cylinder head to a
restrictor elbow in one end of the hollow rocker shaft.
Excess oil is dumped through an oil drain tube at the
other end of the rocket shaft. The oil feed tube and drain
tube are formed higher than the rocker shaft to help
force oil out the holes in the rocker shaft through the oil
hole in the rockers, and keeps the shaft full of oil during
engine shutdown. The restrictor elbow controls oil flow
to the rockers and prevents excessive pressure drop of
the engine oil pressure system. Oil is forced out of the
shaft through the oil hole at each rocker arm location
and into the drilled passage of each rocker arm, pro-
viding lubrication for the rocker arm bushing. The oil
spills down at the front end over the push rods and valve
springs and drains back to the oil pans.
14-77. Removal and Disassembly.
a. Symptoms and Isolation of Malfunction.
A mal -
function of the cylinder head assembly or valve-
operating component is usually indicated by loss of
engine power, erratic engine speed, or heavy black
exhaust smoke. These symptoms are a result of
compression losses caused by a leaky head gasket,
cracked cylinder head, burned, valve, bent, worn, or
broken push rod, or a defective rocker arm. To iso-
late the cause of the malfunction, proceed as follows:
(1) Remove the valve cover and observe the
rocker arms with the engine running. If one of the
rocker arms or push rods has failed, it can usually
be detected by comparing the motion of all the rocker
(2) One by one, slightly loosen the fuel input
line to each injector with the engine running. This
stops fuel to the cylinder.
If the engine speed and sound
does not change when the fuel to the cylinder is reduced,
a valve in that cylinder has probably failed. Tighten
each fuel line after check has been made. To verify a
valve failure, remove one at a time the fuel injector
for each cylinder and perform compression tests using
a 0-700 psi gauge. The compression pressure at sea
level with engine at cranking speed, 150 rpm (use dead
crank switch) and hot should be 400 ±15 psi.
(3) A leaky head gasket or a crack in the head
can usually be determined by visual inspection. Signs
of coolant leakage will be evident at the point where
the head mates with the block if the gasket is bad. A
crack in the cylinder head is usually indicated by the
presence of an irregular hairline surrounded by signs
of coolant leakage or a black deposit of exhausted
(4) If and of the above checks indicate failure of
a cylinder head component, proceed with the removal
and repair procedures.
b. Cylinder Head and Rocker Arm Shaft Assembly
(1) Refer to Operator and Organizational Main-
tenance Manual to drain the cooling system, disconnect
ether starting aid and remove, the turbocharger, in-
take and exhaust manifold, nozzle holder assemblies
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