Jeep XJ. Manual — part 284
Oil Lubrication System—2.5L 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
9 - 4
2.5L ENGINE
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DESCRIPTION AND OPERATION (Continued)
CYLINDER BLOCK
DESCRIPTION
The cylinder block is a cast iron inline four cylin-
der design. The cylinder block is drilled forming gal-
leries for both oil and coolant.
CYLINDER HEAD
DESCRIPTION
The cylinder head is made of cast iron containing
eight valves made of chrome plated heat resistant
steel, valve stem seals, springs, retainers and keep-
ers. The cylinder head, valve seats and guides can be
resurfaced for service purposes.
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.
The valve guides are integral to the cylinder head,
They are not replaceable. However, they are service-
able.
CRANKSHAFT
DESCRIPTION
The crankshaft is constructed of nodular cast iron.
Fig. 3 Cylinder Block—2.5L
1 – CYLINDER BLOCK
Fig. 4 Cylinder Head
1 – CYLINDER HEAD BOLTS
2 – CYLINDER HEAD GASKET
3 – CYLINDER HEAD
Fig. 5 Crankshaft—Typical
1 – MAIN BEARING JOURNALS
2 – COUNTER BALANCE WEIGHTS
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2.5L ENGINE
9 - 5
DESCRIPTION AND OPERATION (Continued)
PISTON AND CONNECTING ROD
DESCRIPTION
The pistons are made of a high strength aluminum
alloy, the piston skirts are coated with a solid lubri-
cant (Molykote) to reduce friction and provide scuff
resistance. The connecting rods are made of cast iron.
CAMSHAFT
DESCRIPTION
The camshaft is made of cast iron with eight
machined lobes and four bearing journals.
OPERATION
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.
OPERATION
When the push rods are forced upward by the cam-
shaft lobes the push rod presses upward on the
rocker arms, the rocker arms pivot, forcing down-
ward pressure on the valves forcing the valves to
move downward and off from their seats.
VALVES
DESCRIPTION
The valves are made of heat resistant steel and
have chrome plated stems to prevent scuffing. All
valves use three bead lock keepers to retain the valve
spring and promote valve rotation (Fig. 9).
Fig. 6 Piston and Connecting Rod Assembly
Fig. 7 Camshaft—Typical
1 – CAMSHAFT
2 – LOBES
3 – BEARING JOURNAL
Fig. 8 Rocker Arms—Typical
1 – CAPSCREWS
2 – BRIDGE
3 – PIVOT ASSEMBLY
4 – PUSH RODS
5 – ROCKER ARMS
9 - 6
2.5L ENGINE
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DESCRIPTION AND OPERATION (Continued)
VALVE SPRING
DESCRIPTION
The valve springs are made of high strength
chrome silicon steel. The springs are common for
both intake and exhaust valves.
CYLINDER HEAD COVER
DESCRIPTION
The cylinder head cover is made of die cast alumi-
num and incorporates the Crankcase Ventilation
(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.
Fig. 9 Valve and Keeper Configuration 2.5L 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
1 – AIR INLET FITTING
2 – CYLINDER HEAD COVER
3 – FIXED ORIFICE FITTING
Fig. 11 Oil Pan
1 – OIL PAN
2 – OIL PAN DRAIN PLUG
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2.5L ENGINE
9 - 7
DESCRIPTION AND OPERATION (Continued)
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