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, inspect camshaft for
wear.
4
VALVE FACE AND
SEAT
GRINDING
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.
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 unevennessof 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
necesary to true a valve indicate whether valve head
is
worn or warped.
WARPED
VALVE
WITH
KNIFE EDGE KNIFE EDGE
GOODMARGIN
I
I
I
.030lNCHMlNlMUM
(.E
MM)
M-1184
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 manufacturer's
directions.
Valve seats should be ground with a
45
degree stone
and the width
of
the seat band should be
1
/32 inch to
3/64 inch
(0.8
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 thevalve 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.
VT-1021
FIGURE
6.
VALVE INTERFERENCE ANGLE
10-5
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