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

The K-Line bronze valve-guide insert is
installed in a similar manner as the castiron
insert. The existing guide is reamed
oversize and the thin-wall insert-approximately
0.060-inch thick-is installed
kith a special driver. Once in place, the
excess material is trimmed off. The guide
is expanded and reamed to size using the
original valve seat as a pilot to prevent
tilting the valve guide. This should be
done when reaming any type of guide.
VALVE INSPECTION AND
RECONDITIONING
After getting your valve guides in
shape, next on the list are the valves
themselves. You should have already
checked them for obvious damage such as
burnt heads and excessively worn tips,
particularly if your engine is the pre-'72
429 with rail rocker arms.
Measure Valve-Stem Wear-3 51 C, 351 MI
400 and 4291460 engines use valves with
nominal 11132-inch stem diameters. More
precisely, 351 C and 351M1400 valve-stem
diameters are 0.3416-0.3423 inch for
the intakes and 0.341 1-0.3418 inch for
the exhausts. 4291460 intake and exhaustvalve
stems are the same diameter at
0.3416-0.3423 inch. The reason for the
smaller 351 C and 351 MI400 exhaustvalve
stem is to provide the proper hot
stem-to-guide clearance as all valve guides
are reamed to the same diameter.
Use the preceding figures to check for
stem wear, or you can compare the worn
and unworn portion of each valve stem to
determine exact wear. Maximum stem
wear usually occurs at the tip end of a
valve. This area is easily recognizable as
the shlny portion of the valve stem.
There's a sharp division between it and
the unworn surface. Maximum valve
opening is represented by the end of the
shiny surface at the tip end. This is where
a valve stops in its guide at its full-open
position.
You'll need a- 1-inch micrometer to
check valve-stem wear. Measure the stem
diameters immediately above and below
the maximum-wear line, then subtract to
determine wear.
Now that you've come up with a figure
for valve-stem wear, the question is
how mu'ch is acceptable Again, this depends
on the service you expect from
your engine after the rebuild, if and how
you reconditioned the valve guides and a
myriad of other questions that makes
arriving at an exact wear figure impossible.
However, concentrating on desired
service and the type of reconditioning
you did on your guides, you should be
able to answer this question.
Measuring valve-stem wear by comparing valve stem's worn and unworn portion. You'll
find them directly below and above the wear line on valve's tip-end. This valve was replaced
because I decided 0.001 5 inch wear was too much for the additional mileage planned
for the engine.
Reconditionlllu ran.-. rwa. rllllu LII= tip square to Its stem-just enough to remove any
signs of wear. Then chamfer tip to remove the sharp edge. Face isground to a 44' angle to
create a positive seal with 45" seat in head.
First, taking both ends of the spectrum,
if valves with more than 0.002-inch
wear are installed in guides with more
than the 0.005-inch stem-clearance limit
or in guides reconditioned by knurling,
the time spent on head work to this point
could've been saved by leaving the heads
alone. Knurling is a Band-Aid fix rather
than a true rebuilding method. It's like
wrapping tape around a radiator hose to
repair a leak instead of replacing the hose.
The problem is not cured, it's just delayed.
On the other hand, new valves or
used ones with no more than 0.001-inch
stem wear installed in guides reconditioned
with bronze inserts should pro-
vide better-than-original service.
My suggestion is that you install valves
with no more than 0.002-inch stem wear.
Set this as your absolute minimum when
deciding on which avenue to take when
dealing with valve-stem and valve-guide
wear. This should give you at least half
the durability of new valves and guides.
Reconditioning Your Valves-Assuming
your valves checked OK, have them reconditioned.
Grind their faces and tips.
The face is the valve surface which contacts
the cylinder-head valve seat. A perfect
seal must be made to seal the combustion
chamber from the intake and exhaust
ports when the valve is held closed