Piston-Fitting - Jeep cherokee 2000 Service Manual

XJ
SERVICE PROCEDURES (Continued)
inch). If the measurement differs from specification
by more than 0.076 mm (0.003 inch), ream the guide
bore to accommodate an oversize valve stem.
ALTERNATIVE METHOD:
(1) Use a dial indicator to measure the lateral
movement of the valve stem (stem-to-guide clear-
ance). This must be done with the valve installed in
its guide and just off the valve seat (Fig. 16).
(2) Correct clearance
(0.001-0.003 inch). If indicated movement exceeds the
specification ream the valve guide to accommodate
an oversize valve stem.
NOTE: Valve seats must be ground after reaming
the valve guides to ensure that the valve seat is
concentric to the valve guide.
Fig. 16 Measurement of Lateral Movement Of Valve
1 – DIAL INDICATOR
VALVE SPRING TENSION TEST
Use a Universal Valve Spring Tester and a torque
wrench to test each valve spring for the specified ten-
sion value (Fig. 17).
Replace valve springs that are not within specifica-
tions.
PISTON—FITTING
BORE GAUGE METHOD
(1) To correctly select the proper size piston, a cyl-
inder bore gauge, capable of reading in 0.003 mm
(.0001 in.) INCREMENTS is required. If a bore
gauge is not available, do not use an inside microme-
ter.
is 0.025-0.0762
Stem
mm
Fig. 17 Valve Spring Tester
1 – TORQUE WRENCH
2 – VALVE SPRING TESTER
(2) Measure the inside diameter of the cylinder
bore at a point 49.5 mm (1-15/16 inches) below top of
bore. Start perpendicular (across or at 90 degrees) to
the axis of the crankshaft at point A and then take
an additional bore reading 90 degrees to that at point
B (Fig. 19).
(3) The coated pistons will be serviced with the
piston pin and connecting rod pre-assembled. The
coated piston connecting rod assembly can be
used to service previous built engines and
MUST be replaced as complete sets. Tin coated
pistons should not be used as replacements for coated
pistons.
(4) The coating material is applied to the piston
after the final piston machining process. Measuring
the outside diameter of a coated piston will not pro-
vide accurate results (Fig. 18). Therefore measuring
the inside diameter of the cylinder bore with a dial
Bore Gauge is MANDATORY. To correctly select the
proper size piston, a cylinder bore gauge capable of
reading in 0.003 mm (.0001 in.) increments is
required.
(5) Piston installation into the cylinder bore
requires slightly more pressure than that required
for non-coated pistons. The bonded coating on the
piston will give the appearance of a line-to-line fit
with the cylinder bore.
2.5L ENGINE 9 - 17