Pistons (8-Cylinder) - Jeep 1979 CJ-5 Technical & Service Manual

1B-60
ENGINES
Measuring taring Clearance with Plastigage
(1) Wipe bearing inserts and rod journal clean.
(2) Lubricate upper insert and install in rod.
(3) Place strip of Plastigage across full width of
lower insert at center of bearing cap. Lower insert must
be dry.
(4) Install bearing cap to connecting rod and tighten
retaining nuts to 33 foot-pounds (45 N«m) torque.
NOTE: Do not rotate crankshaft. Plastigage will shift,
resulting in inaccurate reading. Plastigage must not
crumble, If brittle, obtain fresh stock.
(5) Remove bearing cap and determine amount of
clearance by measuring width of compressed Plastigage
with scale on Plastigage envelope (fig. 1B-94).
SCALE
COMPRESSED
P L A S T I G A G E
4 1 9 0 7
Fig. 1B-94
Connecting Rod Bearing Cleiraice Measurement
will Plastigage
(6) If correct clearance is indicated, bearing fitting
is not necessary. Remove Plastigage from crankshaft
and bearing and proceed to Installation.
NOTE: Traces of Plastigage left on bearing surfaces
will dissolve in hot oil when engine is running.
(7) If oil clearance exceeds specification, install
0.001-inch undersize bearing inserts and check clearance
as described in steps (1) through (5).
The clearance indicated with 0.001-inch undersize
bearing installed will determine if 0.001-inch undersize
inserts or some other combination are needed to provide
correct clearance. For example, if the initial clearance
was 0.003 inch (0.076 mm), 0.001-inch undersize inserts
would reduce clearance by 0.001 inch (0.025 mm). Oil
clearance would be 0.002 inch (0.051 mm) and within
specifications. A 0.002-inch undersize insert and a 0.001-
inch undersize insert would reduce this clearance an
additional 0.0005 inch (0.013 mm). Oil clearance would
then be 0.0015 inch (0.038-mm).
CAUTION: Never use inserts which differ more than
one bearing size as a pair. For example, do not use a
standard upper and 0.002-inch undersize lower.
(8) If oil clearance exceeds specification when 0.002-
inch undersize inserts are installed, measure connecting
rod journal with micrometer. If journal size is correct,
inside diameter of connecting rod is incorrect and rod
must be replaced.
NOTE: Journal may have been ground 0.010-inch
(0.254 mm) undersize.
If journal size is incorrect, replace crankshaft or grind
journal to accept a suitable undersized bearing.
Measuring Connecting Rod Journal with Micrometer
(1) Wipe connecting rod journal clean.
(2) Use micrometer to measure journal diameter at
two points 90° apart at each end of journal. Note differ-
ence between maximum and minimum diameters.
(3) Refer to Specifications for maximum allowable
taper and out-of-round. If any rod journal is outside
specifications, replace crankshaft or recondition crank-
shaft and fit with undersize bearing inserts.
(4) Compare maximum reading obtained with jour-
nal diameters listed in bearing fitting chart.
(5) Select inserts required to obtain specified bear-
ing clearance.
NOTE: Always check clearance with Plastigage after
installing replacement bearings. Check clearance of each
journal when installing crankshaft kit (crankshaft sup-
plied with bearings).
Installation
(1) Rotate crankshaft to position connecting rod
journal at bottom of stroke.
(2) Lubricate bearing surface of each insert with
clean engine oil.
(3) Install bearing inserts, cap and retaining nuts.
Tighten to 33 foot-pounds (45 N*m) torque.
CAUTION: Be careful when rotating the crankshaft
with bearing caps removed. Be sure the connecting rod
screws do not accidentally come in contact with the rod
journals and scratch the finish, which can cause bearing
failure. Short pieces rubber hose slipped over rod screws
will provide protection during installations.
(4) Install oil pan using replacement gaskets and
seals. Tighten drain plug securely.
(5) Fill crankcase to specified level with clean oil.
PISTONS
Aluminum alloy autothermic pistons are steel rein-
forced for strength and controlled expansion.