Pontiac tempest 1968 Service Manual page 284

V-8 E N G I N E
8-67
and fitting of pistons should be closely coordinated.
If bore has been honed, it should be washed thor­
oughly with hot soapy water and a stiff bristle brush.
Using a cylinder checking gauge, measure the cyl­
inder bore crosswise of the block to find the smallest
diameter. Record the smallest diameter of each
bore.
NOTE: When measuring cylinder bores and pis­
tons ii is very important that the block and pistons
be at room temperature. If any or all of the parts
are hotter or colder than normal room tempera­
ture, improper fitting will result.
Measure the piston skirt perpendicular to the pis­
ton pin boss (piston pin removed) and at sizing point
indicated in F i g . 6-119.
Make sure the micrometer is In full contact (Fig.
6-120).
As the pistons are measured they should be marked
for size identification and the measurements recorded.
If there is excessive clearance between a cylinder
bore and the piston which was installed In that bore,
a new piston should be used.
New pistons are serviced in standard size and .001",
.002", .005", .010", .020" and .030" oversize.
NOTE: Since these are nominal or basic sizes, ii
is important that new pistons be measured to en­
sure proper fit. All new pistons are serviced with
selectively fitted piston pins.
After all measurements have been made, match the
new pistons with cylinders where they will fit with
proper clearance. Honing of cylinder bore may be
necessary to effect a proper fit. When properly
mated, mark pistons with cylinder numbers they fit
so they will not become mixed.
FITTING PIN I N PISTON
The piston p i n f i t In the piston is .0005" to .0007"
loose with pin and bosses clean and d r y .
F i g . 6-120 Measuring Piston
NOTE: Piston and pin must be at room tempera­
ture when checking fit and pin must be able to fall
from piston by its own weight.
FITTING OVERSIZE PINS I N PISTONS
AND CONNECTING ROD PIN BORES
In case the standard size piston pin does not fit
properly in the piston, an oversize piston pin must
be fitted. Piston pins are available in .001" and
.003" oversize.
When oversize pins are used, the piston pin bosses
must be honed to give required fit. It will also be
necessary to hone the connecting rod pin bore to fit
the oversize pin, using a Sunnen hone or similar
accurate equipment.
NOTE: A special grit hone is used for honing the
connecting rod pin bore. The piston pin size should
be .0008" to .0016" larger than connecting rod pin
bore for proper press fit. The piston pin should
not show any movement under 1500 lb. minimum
load after assembly in rod.
ASSEMBLE CONNECTING ROD T O PISTON
There is a notch cast in the top of all piston heads
to facilitate proper installation. The piston assem­
blies should always be installed with notch toward
front of engine. Position rod in piston so that oil
squirt hole (Fig. 6-121) is toward camshaft.
R E P L A C E PISTON PIN
1. Place pilot plunger and spring in the support
base to be used as a pilot end stop. See Fig. 6-122
insert for correct base support and pilot plunger for
type pistons being serviced.
2. Place pilot plunger of tool J 6901 in piston pin
bore and place on arbor press.
3. Coat piston pin and rod lightly with graphite
lubricant.
4. Place tool J 6901-3 in piston pin and press pin
into piston and connecting rod (Fig. 6-122) until
piston pin bottoms against plunger of tool J 6901.
Piston must turn freely on pin. If piston binds on
pin, disassemble, hone piston pin bosses slightly and
reassemble.
PISTON RINGS-REPLACE
1. Remove piston and rod assembly. See CON­
NECTING ROD AND PISTON A S S E M B L Y - R E MOVE
AND R E P L A C E .
2. Remove piston rings using J 7117 or J 22563.
3. Clean carbon, varnish, and gum from piston
surfaces, including under side of piston head. Clean
ring grooves, and oil holes in oil ring groove, using
suitable cleaning tools and'solvent.