How To Rebuild Your Ford V-8 351C-351M-400-429-460.pdf - Index of

30' TOP CUT
INCH WIDTH
L
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Exhaust valves should have no less than a
1 /32-Inch margln after grinding. Otherwlse
there Is a risk of burning It. Intake-valve
margins shouldn't be thinned beyond 1 /64-
Inch.
by the valve spring.
Valve faces are ground on a special
grinder made just for this purpose. The
valve is rotated in a collet-type chuck at
an angle of 44' to a fast-turning grinding
wheel. As the valve face rotates against
the wheel's rotation, it is also oscillated
across the face of the grinding wheel.
Simultaneously, the valve and stone are
bathed in cutting oil for cooling and to
wash away the grindings. Enough face
material is removed only to expose new
metal on the valve face. If too much
material is removed, the valve's margin
will be thinned excessively and the valve
will have to be junked. The margin of a
valve is the thickness at its OD, at the
outer edge of the face.
A valve with little or no margin will
approach being sharp at its outer edge
and must be replaced because it's highly
susceptible to burning, particularly if it's
an exhaust valve. An exhaust-valve margin
should be at least 0.030 inch wide-ap-
A valve seat Is ground to a 45" angle, then Its outside and Inside diameters are established
by 30" top and 60" bottom cuts. A seat's outside diameter should be approximately 1 /I 6-
inch smaller than the outside diameter of the valve's face. Top and bottom cuts also
establish seat width.
proximately 1/32 inch, if you prefer
fractions. Because an intake doesn't
operate as hot as an exhaust valve, its
margin can be as narrow as 0.015 inchapproximately
1/64 inch.
After the valve face is ground, the tip
is faced, or ground square to the centerline
of the valve stem, using another
attachment on the valve-grinding machine.
Finally, the tip is beveled, or chamfered
to eliminate the sharp edge developed
during the facing operation. Your valves
should now be as good as new and ready
for assembly into the cylinder headswhen
the heads are ready. It's now unnecessary
to keep your valves in order
because all traces -of mating to other
components are gone.
operate. This is a job for the specialist
and it's an essential part of every rebuild.
Seat reconditioning is particularly necessary
for heads with reconditioned guides
because the seats will not be concentric
with the new guides-they won't have the
same centers. Consequently, even though
a valve seat may be in good condition, the
guide won't let the valve seat evenly when
it's closed. It will be held off-center in
relation to the seat and cannot seat when
fully closed. Because a valve seat is
ground using a mandrel centered in the
valve guide, the seat will be concentric
with the guide.
Grinding the Seats-Valve seats are ground
using a manual, electric- or air-powered
grinder alternating between three grindingstones
with angles of 30°, 45' and 60".
Power tools are best because they provide
the most accurate seat. The critical angle,
VALVE-SEAT RECONDITIONING
Valve seats are reconditioned just like
valves-by grinding. Equipment for valve 45", is the valve-seat angle. If this 4.5'
seats is special, expensive and requires figure strikes you wrong, it's because the
some degree of skill and experience to valves were ground to a 44O angle. The
Freshly dressed 60"' 45" and 30' stones ready to grind valve seats. I start with the 45"
stone. After the seat cleans up-removing as little material as possible, zero in on seat
width with the 30" and 60" stones.