TAPPETS
Very little wear takes place on tappet diameters or in
tappet bores.
If
the
clearance
between tappet
and
bore in cylinder block exceeds specifications, replace
the tappet.
Inspect the tappet faces which contact camshaft
lobes for roughness, scuffing, or concave wear.
Replace any worn tappets. If tappets are worn,
VALVE FACE AND SEAT GRINDING
Some engines are equipped with a premium valve
package (aluminized intakevalves).
If
the aluminized
valve face does not clean-up using a wire brush, the
valve face may be refinished. This removes the
aluminized coating from thevalveface. An aluminized
valve that has been refinished will normally have a life
expectancy equal to a standard valve. If longer valve
life is required, worn or damaged valves should be
replaced with new premium valves.
*
,
inspect camshaft for wear.
Before installing new valves or previously used valves,
inspect valve seats for proper valve seating.. If used
valves are reinstalled, the valve stems should be
cleaned and valve faces ground to their specified
angles of 44". Refinish valve seats to a 45" angle.
When refacing valves and seats, remove all evidence
of pitting and grooving.
If
end of valve stem is pitted
or worn, true
it
and clean
it
up
on
the refacer wheel.
A
very light grind is usually enough to square stem and
remove any pits or burrs. The valve guide should be
thoroughly cleaned. If valve guide is worn, or valve is
warped, the necessary parts must be replaced.
By
grinding the valve face and seat at slightly different
angles, a fine line of contact on face and seat is
obtained, eliminating the need to lap the seating sur-
faces. The one degree difference in angles is defined as
the interference angle (Figure 6). The seat angle is
greater than that of the valve face. This assures contact
at the maximum diameter on valve seat seating surface.
VT-1021
FIGURE
6.
VALVE INTERFERENCE ANGLE
Refinish valve faces to a 44" angle on a valve refacing
machine. The first cut from valve face
must
be a light
grinding. Check if there is an unevenness of metal being
removed.
If
only
part
of
valve's
face
has
been
touched,
check to see if valve is properly seated in machine or
if
valve is warped, worn,
or
distorted. When cut is even
around the whole valve face, keep grinding until com-
plete face is ground clean. Be sure the correct valve
face angle is maintained. When valve head
is
warped, a
knife edge will be ground (Figure
7)
on part or all of the
head due to the large amount of metal that must be
removed to completely reface valve. Heavy valve heads
are required for strength and good heat dissipation.
Knife edges lead
to
breakage, burning, and pre-ignition
due to heat localizing on the edge.
Replace any valve that cannot be entirely refaced while
keeping a good valve margin (Figure
7)
or is warped,
worn, or damaged in any way. The amount of grinding
necessary to true a valve indicates whether valve head
is worn or warped.
WARPED
VALVE
WITH
KNIFE EDGE KNIFE EDGE
GOOD MARGIN
74
1/16
INCH
1
I
(1.6mm)MlNlMUM
M-1114
FIGURE
7.
VALVE
HEAD
MARGIN
When new valve seats are installed, or previously
used seats reground, refinishing must be done with a
valve seat grinder used according to the manufac-
turer's directions.
Valve seats should be ground with a 45 degree stone
and the width of theseat band should be 1/32 inch to
3/64 inch
(0.79
to 1.2 mm) wide. Grind only enough
to assure proper seating.
Place each valve in its proper location. Check each
valve for a tight seat. Make several marks at regular
intervals across the valve face using machinist's
bluing. Observe if the marks rub off uniformly when
the valve is rotated part of a turn against the seat. The
valve seat should contact the valve face evenly at all
points. The line of contact should be at the center of
the valve face.
10-5
Redistribution or publication of this document,
by any means, is strictly prohibited.
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