Repair Damaged Or Worn Threads; Service Engine Assembly (Short Block) - Jeep 1997 Grand Cherokee Service Manual

9 - 4 ENGINE
GENERAL INFORMATION (Continued)
or the Plastigage may be smeared, giving inac-
curate results.
Fig. 2 Placement of Plastigage in BearingShell
(2) Remove the bearing cap and compare the width
of the flattened Plastigage with the scale provided on
the package (Fig. 3). Plastigage generally comes in 2
scales (one scale is in inches and the other is a met-
ric scale). Locate the band closest to the same width.
This band shows the amount of clearance. Differ-
ences in readings between the ends indicate the
amount of taper present. Record all readings taken
(refer to Engine Specifications).
Fig. 3 Clearance Measurement
(3) Plastigage is available in a variety of clearance
ranges. The 0.025-0.076 mm (0.001-0.003 inch) range
is usually the most appropriate for checking engine
bearing clearances.
CONNECTING ROD BEARING CLEARANCE
Engine connecting rod bearing clearances can be
determined by use of Plastigage, or equivalent. The
following is the recommended procedures for the use
of Plastigage:
(1) Remove oil film from surface to be checked.
Plastigage is soluble in oil.
(2) Place a piece of Plastigage across the entire
width of the bearing cap shell (Fig. 2). Position the
Plastigage approximately 6.35 mm (1/4 inch) off cen-
ter and away from the oil holes. In addition, suspect
areas can be checked by placing the Plastigage in the
suspect area.
PLASTIGAGE
(3) The crankshaft must be turned until the con-
necting rod to be checked starts moving toward the
top of the engine. Only then should the rod cap with
Plastigage in place be assembled. Tighten the 4.0L
rod cap nut to 45 N·m (33 ft. lbs.) torque. Tighten the
5.2/5.9L rod cap nut to 61 N·m (45 ft. lbs.) torque.
DO NOT rotate the crankshaft or the Plastigage
may be smeared, giving inaccurate results.
(4) Remove the bearing cap and compare the width
of the flattened Plastigage with the scale provided on
the package (Fig. 2). Plastigage generally comes in 2
scales (one scale is in inches and the other is a met-
ric scale). Locate the band closest to the same width.
This band shows the amount of clearance. Differ-
ences in readings between the ends indicate the
amount of taper present. Record all readings taken
(refer to Engine Specifications).
(5) Plastigage is available in a variety of clearance
ranges. The 0.025-0.076 mm (0.001-0.003 inch) range
is usually the most appropriate for checking engine
bearing clearances.

REPAIR DAMAGED OR WORN THREADS

Damaged or worn threads can be repaired. Essen-
tially, this repair consists of:
• Drilling out worn or damaged threads.
• Tapping the hole with a special Heli-Coil Tap, or
equivalent.
• Installing an insert into the tapped hole to bring
the hole back to its original thread size.
CAUTION: Be sure that the tapped holes maintain
the original center line.
Heli-Coil tools and inserts are readily available
from automotive parts jobbers.

SERVICE ENGINE ASSEMBLY (SHORT BLOCK)

A service replacement engine assembly (short
block) may be installed whenever the original cylin-
der block is defective or damaged beyond repair. It
consists of the cylinder block, crankshaft, piston and
rod assemblies. If needed, the camshaft must be pro-
cured separately and installed before the engine is
installed in the vehicle.
A short block is identified with the letter "S"
stamped on the same machined surface where the
build date code is stamped for complete engine
assemblies.
Installation includes the transfer of components
from the defective or damaged original engine. Fol-
low the appropriate procedures for cleaning, inspec-
tion and torque tightening.
ZG