03-oo-25
Engine-Service
03-oo-25
SERVICE PROCEDURES (Continued)
Piston Ring End Gap
1 . Measure gap between ends of piston ring with
Feeler Gauge 081L-4201-A or equivalent. If ring
gap is less than or greater than specified limits,
try another piston ring set. For Specifications,
refer to Section 03-0 1 A (3.8L) or Section 03-01 8
(4.6L).
If
end gap is greater than service limit, replace
piston ring. If end gap exceeds service limit, even
with a new piston ring, rebore cylinder blocks.
A15062-B
2. Piston rings should be staggered on the piston to
make sure the piston ring end gaps are not
aligned.
Piston Pin-to-Piston Clearance
Check the outside diameter of the piston pin and the
inner diameter (10) of the pin bore in the piston as
described. Replace any piston pin or piston that is not
within specifications. For Specifications, refer to
Section 03-D 1 A (3.8L) or Section 03-01 B (4.6L).
Piston Outer Diameter
Measure the piston diameter using a micrometer.
Measure piston skirt diameter 90 degrees to piston pin
center axis, 42 mm ( 1 .65 inches) from piston dome.
It may be necessary periodically to use another piston
(within the same grade size) that is either slightly
larger or smaller to achieve the specified clearance.
Piston Rings
CAUTION: Piston rings should not be transferred
from one piston to another, regardless of mileage
or piston ring failure may occur.
Replace all piston rings that are scored, broken,
chipped or cracked. Check the end gap and side
clearance as described.
Piston Ring-to-Groove Clearance
NOTE:
If
lower lands have high steps, piston should be
replaced.
Check piston ring side clearance of compression rings
with Feeler Gauge 081 L -420 1-A or equivalent
inserted between piston ring and its lower land. Gauge
should slide freely around entire piston ring
circumference without binding. Any wear that occurs
will form a step at inner portion of lower land.
If
clearance is greater than service limit, replace piston
ring. If clearance exceeds service limit, even with a
new piston ring, replace piston.
CHECK PISTON RING SIDE
CLEARANCE USING FEELER
GAUGE 081 L-4201 -A
Piston Pin Hole Diameter
Measure each piston pin hole diameter at the four
points shown.
A14483-B
Replace piston that is not within specifications. For
Specifications, refer to Section 03-Q 1 A (3.8L) or
Section 03-D 1 B (4.6L).
1997 Thunderbird, Cougar July 1996