Jeep Cherokee (XJ): Description and operation
DESCRIPTION The 2.5 liter (150 CID) four-cylinder engine is an
In-line, lightweight, overhead valve engine.
This engine is designed for unleaded fuel. The engine
cylinder head has dual quench-type combustion chambers
that create turbulence and fast burning of the air/
fuel mixture. This results in good fuel economy.
The cylinders are numbered 1 through 4 from front
to rear. The firing order is 1-3-4-2 (Fig. 1).
The crankshaft rotation is clockwise, when viewed
from the front of the engine. The crankshaft rotates
within five main bearings and the camshaft rotates
within four bearings.
The engine Build Date Code is located on a
machined surface on the right side of the cylinder
block between the No.3 and No.4 cylinders (Fig. 2).
The digits of the code identify: FOR EXAMPLE: Code * 801HX23 * identifies a
2.5 liter (150 CID) engine with a multi-point fuel
injection system, 9.1:1 compression ratio and built on
January 23, 1998.
1 - NO. 4 CYLINDER DESCRIPTION A gear-type positive displacement pump is
mounted at the underside of the block opposite the
No. 4 main bearing. OPERATION The pump draws oil through the screen and inlet
tube from the sump at the rear of the oil pan. The oil
is driven between the drive and idler gears and
pump body, then forced through the outlet to the
block. An oil gallery in the block channels the oil to
the inlet side of the full flow oil filter. After passing
through the filter element, the oil passes from the
center outlet of the filter through an oil gallery that
channels the oil up to the main gallery which
extends the entire length of the block.
Galleries extend downward from the main oil gallery
to the upper shell of each main bearing. The crankshaft
is drilled internally to pass oil from the main bearing
journals (except number 4 main bearing journal) to the
connecting rod journals. Each connecting rod bearing
cap has a small squirt hole, oil passes through the
squirt hole and is thrown off as the rod rotates. This oil
throwoff lubricates the camshaft lobes, distributor drive
gear, cylinder walls, and piston pins.
The hydraulic valve tappets receive oil directly
from the main oil gallery. Oil is provided to the camshaft
bearing through galleries. The front camshaft
bearing journal passes oil through the camshaft sprocket to the
timing chain. Oil drains back to the
oil pan under the number one main bearing cap.
The oil supply for the rocker arms and bridged
pivot assemblies is provided by the hydraulic valve
tappets which pass oil through hollow push rods to a
hole in the corresponding rocker arm. Oil from the
rocker arm lubricates the valve train components,
then passes down through the push rod guide holes
in the cylinder head past the valve tappet area, and
returns to the oil pan.
1 - CAM/CRANK MAIN GALLERY (7) DESCRIPTION The cylinder block is a cast iron inline four cylinder
design. The cylinder block is drilled forming galleries
for both oil and coolant.
1 - CYLINDER BLOCK 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 keepers.
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 mixture,
resulting in better fuel economy.
The valve guides are integral to the cylinder head,
They are not replaceable. However, they are serviceable. DESCRIPTION The crankshaft is constructed of nodular cast iron
1 - CYLINDER HEAD BOLTS
1 - MAIN BEARING JOURNALS DESCRIPTION The pistons are made of a high strength aluminum
alloy, the piston skirts are coated with a solid lubricant
(Molykote) to reduce friction and provide scuff
resistance. The connecting rods are made of cast iron.
DESCRIPTION The camshaft is made of cast iron with eight
machined lobes and four bearing journals.
1 - CAMSHAFT 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. DESCRIPTION The rocker arms are made of stamped steel and
have a operational ratio of 1.6:1.
1 - CAPSCREWS OPERATION 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. 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). DESCRIPTION The valve springs are made of high strength
chrome silicon steel. The springs are common for
both intake and exhaust valves.
1 - VALVE LOCKS (3-BEAD) Cylinder head cover DESCRIPTION The cylinder head cover is made of die cast aluminum
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. DESCRIPTION The valve guides are integral to the cylinder head,
They are not replaceable. However, they are serviceable.
1 - AIR INLET FITTING DESCRIPTION The oil pan is made of stamped steel. The oil pan
gasket is a one piece steel backbone silicone coated
gasket.
1 - OIL PAN Valve stem seal DESCRIPTION The valve stem seals are made of rubber and incorporate
a garter spring to maintain consistent lubrication
control (Fig. 9). DESCRIPTION The intake manifold is made of cast aluminum and
uses seven bolts to mount to the cylinder head. This
mounting style improves sealing and reduces the
chance of leaks.
Exhaust manifold DESCRIPTION The exhaust manifold is log style and is made of
high silicon molybdenum cast iron. The exhaust manifold
shares a common gasket with the intake manifold.
The exhaust manifold also incorporates a ball
flange outlet for improved sealing and strain free
connections (Fig. 12).Engine
Fig. 1 Engine Firing Order
Fig. 2 Build Date Code Location
2 - NO. 3 CYLINDER
3 - DAY
4 - MONTH
5 - YEAR
6 - MACHINED SURFACELubrication system
Oil Lubrication System-2.5L Engine
2 - TAPPET GALLERY
3 - TAPPET GALLERY
4 - CAMSHAFT BEARING
5 - NUMBER 1 CAMSHAFT BEARING JOURNAL
6 - CAMSHAFT SPROCKET
7 - TAPPET GALLERYCylinder block
Fig. 3 Cylinder Block-2.5LCylinder head
Crankshaft
Fig. 4 Cylinder Head
2 - CYLINDER HEAD GASKET
3 - CYLINDER HEAD
Fig. 5 Crankshaft-Typical
2 - COUNTER BALANCE WEIGHTSPiston and connecting rod
Fig. 6 Piston and Connecting Rod AssemblyCamshaft
Fig. 7 Camshaft-Typical
2 - LOBES
3 - BEARING JOURNALRocker ARM
Fig. 8 Rocker Arms-Typical
2 - BRIDGE
3 - PIVOT ASSEMBLY
4 - PUSH RODS
5 - ROCKER ARMSValve spring
Fig. 9 Valve and Keeper Configuration 2.5L Engine
2 - RETAINER)
3 - VALVE STEM OIL SEAL)
4 - INTAKE VALVE)
5 - EXHAUST VALVE)
6 - VALVE SPRINGValve guide
Fig. 10 Cylinder Head Cover
2 - CYLINDER HEAD COVER
3 - FIXED ORIFICE FITTINGOil pan
Fig. 11 Oil Pan
2 - OIL PAN DRAIN PLUGIntake manifold
Fig. 12 Intake and Exhaust Manifo
Other materials:
Rearview mirror support bracket. Sunvisors. Headliner
Rearview mirror support bracket
INSTALLATION
(1) Mark the position for the mirror bracket on the
outside of the windshield glass with a wax pencil.
(2) Clean the bracket contact area on the glass.
Use a mild powdered cleanser on a cloth saturated
with isopropyl (rubbing) alcohol. Finally, c ...