Jeep XJ. Manual — part 299
Oil Lubrication System—4.0L Engine
1 – CAM/CRANK MAIN GALLERY (7)
2 – TAPPET GALLERY
3 – TAPPET GALLERY
4 – CAMSHAFT BEARING
5 – NUMBER 1 CAMSHAFT BEARING JOURNAL
6 – CAMSHAFT SPROCKET
7 – TAPPET GALLERY
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4.0L ENGINE
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DESCRIPTION AND OPERATION (Continued)
CYLINDER BLOCK
DESCRIPTION
The cylinder block is a cast iron inline six cylinder
design. The cylinder block is drilled forming galleries
for both oil and coolant (Fig. 3).
CYLINDER HEAD
DESCRIPTION
The cylinder head is made of cast iron containing
twelve valves made of chrome plated heat resistant
steel, valve stem seals, springs, retainers and keep-
ers. The cylinder head and valve seats can be resur-
faced for service purposes.
The valve guides are integral to the cylinder head,
They are not replaceable. However, they are service-
able.
The cylinder head uses dual quench-type design
combustion chambers which cause turbulence in the
cylinders allowing faster burning of the air/fuel mix-
ture, resulting in better fuel economy (Fig. 4).
CRANKSHAFT
DESCRIPTION
The crankshaft is constructed of nodular cast iron.
The crankshaft is a crosshaped four throw design
with eight counterweights for balancing purposes.
The crankshaft is supported by seven select main
bearings with the number three serving as the thrust
washer location. The main journals of the crankshaft
are cross drilled to improve rod bearing lubrication.
The select fit main bearing markings are located on
the crankshaft counter weights. The crankshaft rear
oil seal is a two piece design. The front oil seal is a
one piece design retained in the timing chain cover
(Fig. 5).
Fig. 3 4.0L Cylinder Block with Main Bearing Caps
and Cap Brace
1 – BLOCK
2 – MAIN BEARING CAP BRACE
Fig. 4 Cylinder Head 4.0L Engine
1 – CYLINDER HEAD BOLTS
2 – CYLINDER HEAD GASKET
3 – CYLINDER HEAD
Fig. 5 Crankshaft with Select Fit Marking Location
1 – 1/4” LETTERS
2 – (ROD)
3 – (MAIN)
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4.0L ENGINE
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DESCRIPTION AND OPERATION (Continued)
PISTON AND CONNECTING ROD
DESCRIPTION
The pistons are made of a high strength aluminum
alloy with an anodized top ring groove and crown.
Piston skirts are coated with a solid lubricant
(Molykote) to reduce friction and provide scuff resis-
tance. The connecting rods are made of ductile iron.
A pressed fit piston pin is used to attach the piston
and connecting rod.
CAMSHAFT
DESCRIPTION
The camshaft is made of gray cast iron with twelve
machined lobes and four bearing journals. When the
camshaft rotates the lobes actuate the tappets and
push rods, forcing upward on the rocker arms which
applies downward force on the valves.
ROCKER ARM
DESCRIPTION
The rocker arms are made of stamped steel and
have a operational ratio of 1.6:1. When the push rods
are forced upward by the camshaft lobes the push
rod presses upward on the rocker arms, the rocker
arms pivot, forcing downward pressure on the valves
forcing the valves to move downward and off from
their seats (Fig. 8).
Fig. 6 Piston and Connecting Rod Assembly
Fig. 7 Camshaft—Typical
1 – CAMSHAFT
2 – LOBES
3 – BEARING JOURNAL
Fig. 8 Rocker Arms 4.0L Engine
1 – CAPSCREWS
2 – BRIDGE
3 – PIVOT ASSEMBLY
4 – PUSH RODS
5 – ROCKER ARMS
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4.0L ENGINE
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DESCRIPTION AND OPERATION (Continued)
VALVES
DESCRIPTION
The valves are made of heat resistant steel and
have chrome plated stems to prevent scuffing. All
valves use three bead locks to promote valve rotation
(Fig. 9).
VALVE SPRING
DESCRIPTION
The valve springs are made of high strength silicon
chrome spring steel. The springs are common for
both intake and exhaust valves. (Fig. 9).
CYLINDER HEAD COVER
DESCRIPTION
The cylinder head cover (Fig. 10) is made of
stamped steel and incorporates the Crankcase Venti-
lation (CCV) Hoses and the oil fill opening.
HYDRAULIC TAPPET
DESCRIPTION
Valve lash is controlled by hydraulic tappets
located inside the cylinder block, in tappet bores
above the camshaft.
VALVE GUIDE
DESCRIPTION
The valve guides are integral to the cylinder head,
They are not replaceable. However, they are service-
able.
OIL PAN
DESCRIPTION
The oil pan is made of stamped steel. The oil pan
gasket is a one piece steel backbone silicone coated
gasket.
VALVE STEM SEAL
DESCRIPTION
The valve stem seals are made of rubber and incor-
porate a garter spring to maintain consistent lubrica-
tion control (Fig. 9).
INTAKE MANIFOLD
DESCRIPTION
The intake manifold is made of cast aluminum and
uses eleven bolts to mount to the cylinder head. This
mounting style improves sealing and reduces the
chance of leaks.
Fig. 9 Valve and Keeper Configuration 4.0L Engine
1 – VALVE LOCKS (3–BEAD)
2 – RETAINER
3 – VALVE STEM OIL SEAL
4 – INTAKE VALVE
5 – EXHAUST VALVE
6 – VALVE SPRING
Fig. 10 Cylinder Head Cover
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4.0L ENGINE
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DESCRIPTION AND OPERATION (Continued)
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