Dodge ram truck 3500 1996 Service Manual page 1016

I - 26 3.9L ENGINE B R
DESCRIPTION
Mm O P E R A T I O N (Continued)
ENGINE COMPONENTS
CYLINDER HEAD CQWBP*
A steel-backed silicone gasket.is used with the cyl­
inder head cover. This gasket is reuseable.
CYLINDER HEADS
The alloy cast iron cylinder heads are held in place
by eight bolts. The spark plugs are located in at peak
of the wedge between the valves (Fig. 5).
SPARK SPARK INTAKE
PLUGS PLUG VALVE
E X H A U S T INTAKE EXHAUST
V A I V E VALVES VALVES J9309-35
Fig. 5 Cylinder Head Assembly
VALVES AND VALVE SPRINGS
The valves are arranged in-line and inclined 18°.
The rocker pivot support and the valve guides are
cast integral with the heads.
OIL PUMP
OIL PUMP PRESSURE
The MINIMUM oii pump pressure is 41.4 kPa (6
psi) at curb idle. The MAXIMUM oil pump pressure
is 207-552 kPa (30-80 psi) at 3,000 RPM or more.
CAUTION; If oil pressure is Z E R O at curb idle, DO
NOT run engine at 3,000 RPM.
CRANKSHAFT
A crankshaft that has undersize journals is
stamped with 1/4 inch letters near the notch of the
No. 6 crankshaft counterweight.
F O R E X A M P L E : R2 stamped on the No. 6 crank­
shaft counterweight indicates that the No.2 rod jour­
nal is 0.025 mm (0.001 in) undersize. M4 indicates
that the No. 4 main journal is 0.025 mm (0.001 in)
undersize. R3 M2 indicates that the No. 3 rod journal
and the No. 2 main journal are both 0.025 mm (0.001
in) undersize.
When a crankshaft is replaced, all main and con­
necting rod bearings, should be replaced with new
bearings. Therefore, selective fitting of the bearings
is not required when a crankshaft and bearings are
replaced.
CRANKSHAFT MAIN BEARINGS
Bearing caps are NOT interchangeable and should
be marked at removal to ensure correct assembly.
Upper and lower bearing halves are NOT inter­
changeable. Lower main bearing halves of No.l and 3
are interchangeable.
Upper and lower No. 2 bearing halves are flanged
to carry the crankshaft thrust loads. They are NOT
interchangeable with any other bearing halves i n the
engine. Bearing shells are available in standard and
the following undersizes: 0.25 mm (0.001 in.), 0.051
mm (0.002 in.), 0.076 mm (0.003 in.), 0.254 mm
(0.010 in.) and 0.305 mm (0.012 in.). Never install an
undersize bearing that will reduce clearance below
specifications.
CRANKSHAFT REAR OIL SEALS
The service seal is a two piece, Viton seal. The
upper seal half can be installed with crankshaft
removed from engine or with crankshaft installed.
When a new upper seal is installed, install a new
lower seal. The lower seal half can be installed only
with the rear main bearing cap removed.
S E R V I C E P R O C E D U R E S
PISTON AND CONNECTING ROD ASSEMBLY
The pistons are elliptically turned so that the
diameter at the pin boss is less than its diameter
across the thrust face. This allows for expansion
under normal operating conditions. Under operating
temperatures, expansion forces the pin bosses away
from each other, causing the piston to assume a more
nearly round shape.
All pistons are machined to the same weight,
regardless of size, to maintain piston balance.
The piston pin rotates in t h e piston only and is
retained by the press interference fit of the piston
pin in the connecting rod.
VALVE TIMING
(1) Turn crankshaft until the No. 6 exhaust valve
is closing and No. 6 intake valve is opening.
(2) Insert a 6.350 mm (1/4 in.) spacer between
rocker arm pad and stem tip of No. 1 intake valve.
Allow spring load to bleed tappet down giving, in
effect, a solid tappet.
(3) Install a dial indicator so plunger contacts
valve spring retainer as nearly perpendicular as pos­
sible. Zero the indicator.
(4) Rotate the crankshaft clockwise (normal run­
ning direction) until the valve has lifted 0.254 mm
(0.010 inch). The timing of the crankshaft should