Dodge ram truck 3500 1996 Service Manual page 1017

B R
3.9L ENGINE 9 - 27
S E R V I C E P R O C E D U R E S (Continued)
now read from 10° before top dead center to 2° after
top dead center. Remove spacer.
CAUTION; DO NOT turn crankshaft any further
clockwise, as valve spring might bottom and result
in serious damage.
(5) I f reading is not within specified limits:
(a) Check sprocket index marks.
(b) Inspect timing chain for wear.
(c) Check accuracy of DC mark on timing indica­
tor.
T H I N G CHAIN ST1ETCH
(1) Place a scale next to the timing chain so that
any movement of the chain can be measured.
(2) Place a torque wrench and socket over cam­
shaft sprocket attaching bolt. Apply torque in the
direction of crankshaft rotation to take up slack; 41
N-m (30 ft. lbs.) torque with cylinder head installed
or 20 N-m (15 ft. lbs.) torque with cylinder head
removed. With torque applied to the camshaft
sprocket bolt, crankshaft should not be permitted to
move. I t may be necessary to block the crankshaft to
prevent rotation.
(3) Hold a scale with dimensional reading even
with the edge of a chain link. With cylinder heads
installed, apply 14 N-m (30 ft. lbs.) torque in the
reverse direction. With the cylinder heads removed,
apply 20 N-m (15 ft. lbs.) torque in the reverse direc­
tion. Note the amount of chain movement (Fig. 6).
Fig. 6 Measuring Timing Chain Wear and Stretch
(4) Install a new timing chain, i f its movement
exceeds 3.175 mm (1/8 inch).
FITTING PISTONS
Check the cylinder block bore for out-of-round,
taper, scoring, or scuffing.
Check the pistons for taper and elliptical shape
before they are fitted into the cylinder bore (Fig. 7).
Piston and cylinder wall must be clean and dry.
Specified clearance between the piston and the cylin­
der wall is 0.013-0.038 mm (0.0005-0.0015 in.) at
21°C (70°F).
Piston diameter should be measured at the top of
skirt, 90° to piston pin axis. Cylinder bores should be
measured halfway down the cylinder bore and trans­
verse to the engine crankshaft center line.
Pistons and cylinder bores should be measured at
normal room temperature, 21°C (70°F).
PISTON PIN BORE DIAMETER
A
PISTON
SIZE
A DIA = PISTON DIAMETER
BORE DIAMETER PISTON
SIZE
MIN. mm (IN.) MAX. mm (IN.) MIN. mm (IN.)
MAX. mm (IN.)
A
99.280 (3.9087) 99.294 (3.9092)
99.306 (3.9097) 99.319(3.9102)
B
99.294 (3.9092) 99.306 (3.9097) 99.319(3.9102)
99.332 (3.9107)
C
99.306 (3.9097) 99.319(3.9102) 99.332 (3.9107)
99.344 (3.9112)
D
99.319(3.9102) 99.332 (3.9107) 99.344 (3.9112)
99.357(3.9117)
E
99.332 (3.9107) 99.344 (3.9112) 99.357(3.9117)
99.370(3.9122)
J9509-80
Fig. 7 Piston Measurements
FITTING RINGS
(1) Measurement of end gaps:
(a) Measure piston ring gap 2 in. from bottom of
cylinder bore. An inverted piston can be used to
push the rings down to ensure positioning rings
squarely in the cylinder bore before measuring.
(b) Insert feeler gauge in the gap. The top com­
pression ring gap should be between 0.254-0.508
mm (0.010-0.020 in.). The second compression ring
gap should be between 0.508-0.762 mm
(0.020-0.030 in.). The oil ring gap should be 0.254-
1.270 mm (0.010-0.050 in.).
(c) Rings with insufficient end gap may be prop­
erly filed to the correct dimension. Rings with
excess gaps should not be used.
(2) Install rings, and confirm ring side clearance:
(a) Install oil rings being careful not to nick or
scratch the piston. Install the oil control rings
according to instructions in the package. I t is not
necessary to use a tool to install the upper and