Service Manual

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.
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 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 indicate whether valve head is
worn or warped.
VALVE WITH
WARPED
KNIFE EDGE KNIFE EDGE
GOOD MARGIN
T
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 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
FIGURE 6. VALVE INTERFERENCE ANGLE line of contact should be at the center of the valve face.
10-5