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

will be sealed the first time the valve
closes. Leakage due to poor seating can
cause a warped valve, or a burned valve
and seat.
The other two angles, 30" and 60°, are
the top cut and the bottom cut, respectively.
The 30' and 60" angles are important
for low-valve-lift air flow. The 30'
top cut is on the combustion-chamber
side. It trues up and establishes the seat's
outside diameter. The 60" bottom cut on
the port side establishes seat ID, but more
importantly, valve-seat width. Valve seat
OD should be ground approximately ..,. A
1/16-inch Smaller than the Valve OD.
grinding mandrel wlm 1. s=ed over
After the 30" top cut is made to establish it. Mandrel and stone are rotated with en air or electric tool.
seat OD, the valve seat is narrowed to the
desired width with the 60" bottom cut.
Seat widths of 0.060-0.080 inch are
used. For cooling reasons, exhaust-valve
seats are generally ground to the high side
of the range (wider) to provide additional
valve-to-seat contact. This ensures additional
contact area for valve-to-seat heat
transfer.
Tools which should be on hand to
assist in the grinding process, other than
the actual grinding or machining equipment,
are a set of dividers, Dykem-type
metal bluing, a scale for setting the
dividers for measuring seat OD and
directly measuring valve-seat width and a
special dial indicator for checking valve-
seat concentricity. Bluing allows the seat r g * ,
to show up as a dark ring contrasted
+ - &.
against the top and
bottom cuts, making the seat much easier
to see and measure.
Hand-Lapping Valves-Lapping valves in
is merely grinding a valve face and its seat
together with lapping compound. This
compound or paste is applied to the valve
face, then the valve is rotated back-andforth
in a circular motion while simultaneously
applying light pressure to the
head of the valve.
I'm mentioning valve lapping in case
you are aware of the process and think it
is necessary for valve sealing. Generally
speaking, if a valve face and its seat aren't
ground correctly, lapping won't fix the
problem, and if they are done right,
lapping shouldn't be necessary for proper
valve seating and sealing. So don't waste
your time with lapping. A reputable rebuilder
is your best guarantee.
If you do lap in the valves, be sure to
clean off all the lapping compound.
Grinding compound and engines do not
make good traveling companions. When
you finish lapping each valve, mark it so
you can put it back on the same seat.
Do They Seal-It would be nice to know
if your valves are going to seal before
installing the heads on your engine. This
is so you can do something about it now
if there is a problem. To determine if
your valves are sealing OK, you'll first
have to assemble the valves in the heads.
Either do it temporarily now, then disassemble
the heads for checking and
setting up the valve springs, or complete
the valve-spring checking and setting-up
as outlined in the next few pages, then
assemble the valves in the heads and
check them.
With the valves in place, position the
heads upside down on your bench so the
head-gasket surface is level. Using kerosene,
fill each combustion chamber and
check inside the ports for leaks. If you
don't see any you can consider the valves
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After a valve seat is its
centricity or runout in relation to the valve
guide should be checked with a gage such
as this. Photo courtesy Ford.