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2-28
VALVE SERVICE
ENGINE
(50)
TORQ
UE
WR
ENCH
-;
2-17 RECONDITIONING VALVES
a. Cleaning, Refacing and Reseating Valves
After removal of valves and springs from
cylinder head, scrape all carbon from combus-
tion chamber and
valves.
If
wire brushes are
used for cleaning carbon use care to avoid
scratching valve seats and valve
faces.
Clean
all carbon and gum deposits from valve guides.
Valve faces and valve seats must not be cut
away excessively when using refacing and re-
seating equipment. Only enough metal should
be removed to true up the surfaces and remove
pits.
The valve head will run hotter as its
thickness is decreased.
If
valve head must be
ground until the outer edge is sharp in order
to clean up the face, the valve should be dis-
carded because the sharp edge will run too hot.
Cutting a valve seat results in lowering the
valve spring pressure and increases the width
of the seat. The nominal width of a valve seat
is
.062"
(ljI6")
.
If
valve seat is over
%-t"
wide
after
t
r uing
it should be narrowed by using
the proper 20 degree and 70 degree cutters.
The refacing and reseating operations should
leave therefinished surfaces smooth and true
so that a minimum of lapping with grinding
compound is required. Excessive lapping will
groove the valve face and a grooved valve will
not seat tightly.
Valves
usually are tested after refacing and
seating
by lightly coating the valve face with
prussian
blue and turning the valve against its
seat . This
indicates
whether the seat is concen-
c.
Replacement of Rocker Arm Cover Gasket
Befor e a new gasket is installed, scrape off
all pieces of old gasket from cylinder head,
wash machined surface with suitable solvent
and wipe it dry.
The valve rocker arm cover gasket should be
cemented to the cylinder head instead of the
cover. When gasket is cemented to the cover it
is more easily damaged when removing or in-
stalling cover.
Apply a heavy coat of thick gasket shellac or
cement to gasket surface of cylinder head, allow
it to dry until quite tacky, then press gasket
down evenly and in proper position on cylinder
head.
Install rocker arm cover to hold gasket
in place until cement is thoroughly
dry.
Adjust valve lash (par. 2-14) or make initial
adjustment of hydraulic valve lifters (par.
2-15) .
Figure 2-22-Cylinder Head Bolt Wrenches
Always use an accurate torque wrench when
tightening cylinder head bolts, to insure uni-
form and proper torque on all bolts. Uneven or
excessively tightened bolts may distort cylinder
bores, causing compression loss and excessive
oil consumption. A
%"
Wrench Attachment
KMO 187-1 should be used with the torque
wrench to properly tighten bolts located under
the valve mechanism. See figure 2-22.
Fig u re 2-23-Cylin
der
Head Bolt
Tig ht e nin g Sequence
Tighten cylinder head bolts to 65-70 ft.
lbs
.
torque following the sequence shown in
figure
2-23. Note that this sequence follows a "figure
8" pattern starting with
the
middle bolt on
right
hand side. After installation of
cylinder
head, particularly with the crimped steel gas-
ket,
t
ight en all bolt s a little at a time in proper
sequence
about three times around before final
tightening
to 65-70 ft. lbs.
torque.
After the
engine has been warmed up to
operating
tem-
perature, recheck bolt s and adjust torque as
required.
_~
I
»->:
ATTACHMENT
(KM O 187-11
Cylinder head bolt holes on manifold (left)
side are open to water jacket; therefore bolts
in
stalled
on this side should have threads coated
with sealing compound to avoid water leaks.
On 1948 Series 70 engines, the two bolts
which attach the air cleaner bracket are
Vs"
longer than other bolts and heads are marked
"X".
If
these longer bolts are used elsewhere,
threads may be stripped and the bottoming
bolts will distort cylinder
bores.
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