c.
Inspection.
(1) Check for loose valve seat inserts by
lightly 3-0 tapping head near inserts. A slight looseness,
which can be found only by tapping, when head is cold
and covered with film of oil is n-o objectionable.
(2) If valve seat insert is loose enough to
bounce or cannot be reground, mark for replacement.
(3) If seat area width (2, fig. 3-255)
exceeds 0.125 in. at any point (see A to B), and cannot
be narrowed (1) sufficiently it is unlikely that seat can be
successfully reground.
d. Repair.
(1) Enlarge counterbore to next oversize.
Most inserts are available in standard and oversizes as
shown in table 2-2.
Note. If head was resurfaced and inserts are
to be reused, deepen counterbore only.
(2) ST-257 Valve Seat Insert Tool must be
used to hold and drive cutters. ST-257 must be driven
(e) Insert locating pin into eroded
by an electric motor, figure 3-256.
hole and tighten holddown knob.
(3) Cut counterbore 0.006/0.010 in.
(f) To set depth of reamer assembly,
deeper than insert thickness to permit peening of head to
insert assembly in guide. Place bushing between holder
hold insert.
assembly and reamer adjustable stop collar. Insert
Caution: Be sure to measure insert before
0.005 inch feeler gage between bushing and adjustable
machining head or installing insert in head.
collar; tighten setscrew.
Caution: Take care not to use too large a
reamer, avoid getting head gasket grommet over
liner flange.
(g) Attach drive adapter to half-inch
drill chuck and place grooved end of drive adapter into
reamer assembly.
(h) Ream out eroded water hole until
collar bottoms against tool.
(i) Remove drill, reamer assembly,
holder assembly and holddown adapter.
(j) Drive bushing into reamed hole
with driver. Bushing should protrude about 0.003-to
0.005-in.
(k) If block is to be resurfaced, refer
to e.(2). If not to be resurfaced, file bushing flush with
head, using a wide, flat mill file.
Figure 3-254. Valve seat insert removal
3-46. Valve Seats and Inserts Repair and
Replacement
a. General. The valve seat insert is used to
provide a greater wear-resistant surface than the cylinder
head material and to provide a new seat where an insert
was not used before.
b. Removal. Remove loose or excessively
worn valve seat inserts, which were previously marked
for replacement during cylinder head inspection, with an
insert extracting tool or by striking insert sharply with a
chisel, causing it to crack and release the press fit.
Remove all inserts if head has been resurfaced
Caution: Cover the valve seat with a shop
rag to avoid injury from broken pieces of the seat.
Figure 3-255. Valve seat insert cross-section.
3-90
