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[Jeep Cherokee XJ repair] General engine overhaul procedures 84 85 86 87 88 89 90 91 92 93

Jeep Cherokee XJ General engine overhaul procedures

Engine overhaul – general information

2.4a Remove the oil pressure sending unit (arrow)

2.4a Remove the oil pressure sending unit (arrow)

Refer to illustrations 2.4a and 2.4b It’s not always easy to determine when, or if, an engine should be completely overhauled, as a number of factors must be considered. High mileage is not necessarily an indication that an overhaul is needed, while low mileage doesn’t preclude the need for an overhaul. Frequency of servicing is probably the most important consideration. An engine that’s had reguiar and frequent oil and filter changes, as well as other required maintenance, will most likely give many thousands of miles of reliable service. Conversely, a neglected engine may require an overhaul very early in its life.

2.4b . . . and connect a gauge to check oil pressure

2.4b . . . and connect a gauge to check oil pressure
(inline six-cylinder engine shown) – the sending unit is
located near the oil filter on all models

Excessive oil consumption is an indication that piston rings, valve seals andlor valve guides are in need of attention. Make sure that oil leaks aren’t responsible before deciding that the rings andior guides are bad. Perform a cylinder compression check to determine the extent of the work required (see Section 3).

Check the oil pressure with a gauge installed in place of the oil pressure sending unit (see illustrations) and compare it to the Specifications. If it’s extremely low, the bearings and/or oil pump are probably worn out.

Loss of power, rough running, knocking or metallic engine noises, excessive valve train noise and high fuel consumption rates may also point to the need for an overhaul, especially if they’re all present at the same time. If a complete tune-up doesn’t remedy the situation, major mechanical work is the only solution.

An engine overhaul involves restoring the internal parts to the specifications of a new engine. During an overhaul, the piston rings are replaced and the cylinder walls are reconditioned (rebored and/or honed). If a rebore is done by an automotive machine shop, new oversize pistons will also be installed. The main bearings, connecting rod bearings and camshaft bearings are generally replaced with new ones and, if necessary, the crankshaft may be reground to restore the journals. Generally, the valves are serviced as well, since they’re usually in lessthan- perfect condition at this point. While the engine is being overhauled, other components, such as the distributor, starter and alternator, can be rebuilt as well. The end result should be a like new engine that will give many thousands of trouble free miles. Note: Criticalcooling system components such as the hoses, drivebelts, thermostat and water pump MUST be replaced with new parts when an engine is overhauled. The radiator should be checked carefully to ensure that it isn’t clogged or leaking (see Chapter 31. Also, we don’t recommend overhauling the oil pump – always install a new one when an engine is rebuilt.

Before beginning the engine overhaul, read through the entire procedure to familiarize yourself with the scope and requirements of the job. Overhauling an engine isn’t difficult if you have the right equipment and follow the instructions carefully, but it is time consuming. Plan on the vehicle being tied up for a minimum of two weeks, especially if parts must be taken to an automotive machine shop for repair or reconditioning. Check on availability of parts and make sure that any necessary special tools and equipment are obtained in advance. Most work can be done with typical hand tools, although a number of precision measuring tools are required for inspecting parts to determine if they must be replaced. Often an automotive machine shop will handle the inspection of parts and offer advice concerning reconditioning and replacement. Note: Always wait until the engine has been completely disassembled and all components, especially the engine block, have been inspected before deciding what service and repair operations must be performed by an automotive machine shop. Since the block’s condition will be the major factor to consider when determining whether to overhaul the original engine or buy a rebuilt one, never purchase parts or have machine work done on other components until the block has been thoroughly inspected. As a general rule, time is the primary cost of an overhaul, so it doesn’t pay to install worn or substandard parts. As a final note, to ensure maximum life and minimum trouble from a rebuilt engine, everything must be assembled with care in a spotlessly clean environment.

Cylinder compression check

3.6 A compression gauge with a threaded fitting for the spark plug hole is preferred over the type that requires hand pressure to maintain the seal

3.6 A compression gauge with a threaded fitting for the
spark plug hole is preferred over the type that requires
hand pressure to maintain the seal

1 A compression check will tell you what mechanical condition the upper end (pistons, rings, valves, head gaskets) of your engine is in. Specifically, it can tell you if the compression is down due to leakage caused by worn piston rings, defective valves and seats or a blown head gasket. Note: The engine must be at normal operating temperature and the battery must be fully charged for this check. Also, if the engine is equipped with a carburetor, the choke valve must be all the way open to get an accurate compression reading (if the engine’s warm, the choke should be open).

2 Begin by cleaning the area around the spark plugs before you remove them (compressed air should be used, if available, otherwise a small brush or even a bicycle tire pump will work). The idea is to prevent dirt from getting into the cylinders as the compression check is being done.

3 Remove all of the spark plugs from the engine (see Chapter 1 ).
4 Block the throttle wide open.

5 Detach the coil wire from the center of the distributor cap and ground it on the engine block. Use a jumper wire with alligator clips on each end to ensure a good ground. On fuel-injected vehicles, the fuel pump circuit should also be disabled (see Chapter 4).

6 Install the compression gauge in the number one spark plug hole (see illustration).

7 Crank the engine over at least seven compression strokes and watch the gauge. The compression should build up quickly in a healthy engine. Low compression on the first stroke, followed by gradually increasing pressure on successive strokes, indicates worn piston rings. A low compression reading on the first stroke, which doesn’t build up during successive strokes, indicates leaking valves or a blown head gasket (a cracked head could also be the cause). Deposits on the undersides of the valve heads can also cause low compression. Record the highest gauge reading obtained.

8 Repeat the procedure for the remaining cylinders and compare the results to the Specifications.

9 Add some engine oil (about three squirts from a plunger-type oil can) to each cylinder, through the spark plug hole, and repeat the test.

10 If the compression increases after the oil is added, the piston rings are definitely worn. If the compression doesn’t increase significantly, the leakage is occurring at the valves or head gasket. Leakage past the valves may be caused by burned valve seats andlor faces or warped, cracked or bent valves.

11 If two adjacent cylinders have equally low compression, there’s a strong possibility that the head gasket between them is blown. The appearance of coolant in the combustion chambers or the crankcase would verify this condition.

12 If one cylinder is about 20 percent lower than the others, and the engine has a slightly rough idle, a worn exhaust lobe on the camshaft could be the cause.

13 If the compression is unusually high, the combustion chambers are probably coated with carbon deposits. If that’s the case, the cylinder head(s) should be removed and decarbonized.

14 If compression is way down or varies greatly between cylinders, it would be a good idea to have a leak-down test performed by an automotive repair shop. This test will pinpoint exactly where the leakage is occurring and how severe it is.

Engine removal – methods and precautions

If you’ve decided that an engine must be removed for overhaul or major repair work, several preliminary steps should be taken.

Locating a suitable place to work is extremely important. Adequate work space, along with storage space for the vehicle, will be needed. If a shop or garage isn’t available, at the very least a flat, level, clean work surface made of concrete or asphalt is required.

Cleaning the engine compartment and engine before beginning the removal procedure will help keep your tools and your hands clean.

An engine hoist or A-frame will also be necessary. Make sure the equipment is rated in excess of the combined weight of the engine and accessories. Safety is of primary importance, considering the potential hazards involved in lifting the engine out of the vehicle.

If the engine is being removed by a novice, a helper should be available. Advice and aid from someone more experienced would also be helpful. There are many instances when one person cannot simultaneously perform all of the operations required when lifting the engine out of the vehicle.

Plan the operation ahead of time. Arrange for or obtain all of the tools and equipment you’ll need prior to beginning the job. Some of the equipment necessary to perform engine removal and installation safely and with relative ease are (in addition to an engine hoist) a heavy duty floor jack, complete sets of wrenches and sockets as described in the front of this manual, wooden blocks and plenty of rags and cleaning solvent for mopping up spilled oil, coolant and gasoline. If the hoist must be rented, make sure that you arrange for it in advance and perform all of the operations possible without it beforehand. This will save you money and time.

Plan for the vehicle to be out of use for quite a while. A machine shop will be required to perform some of the work which the do-ityourselfer can’t accomplish without special equipment. These shops often have a busy schedule, so it would be a good idea to consult them before removing the engine in order to accurately estimate the amount of time required to rebuild or repair components that may need work.

Always be extremely careful when removing and installing the engine. Serious injury can result from careless actions. Plan ahead, take your time and a job of this nature, although major, can be accomplished successfully.

Refer to illustrations 5.5a, 5.5b, 5.52, 5. 1 1, 5. 12, 5.20, 5.24a and 5.24b

Warning: The air conditioning system is under high pressure! Have a dealer service department or service station discharge the system before disconnecting any system hoses or fittings.


1 Refer to Chapter 4 and relieve the fuel system pressure (fuelinjected vehicles only), then disconnect the negative cable from the battery.

2 Cover the fenders and cowl and remove the hood (see Chapter 1 1 ). Special pads are available to protect the fenders, but an old bedspread or blanket will also work.

3 Remove the air cleaner assembly (see Chapter 4).

4 Drain the cooling system (see Chapter 1).

5 Label the vacuum lines, emissions system hoses, wiring connectors, ground strap and fuel lines, to ensure correct reinstallation (see illustration), then detach them (see illustrations). If there’s any possibility of confusion, make a sketch of the engine compartment and clearly label the lines, hoses and wires.

5.5a Label both ends of each wire before unplugging the connector

5.5a Label both ends of each wire before unplugging
the connector

6 Label and detach all coolant hoses from the engine.

7 Remove the cooling fan, shroud and radiator (see Chapter 3).

8 Remove the drivebelt(s) (see Chapter 1 ).

9 Warning: Gasoline is extremely flammable, so extra precautions must be taken when working on any part of the fuel system. DO NOT smoke or allow open flames or bare light bulbs near the vehicle. Also, don’t work in a garage if a natural gas appliance with a pilot light is present. Disconnect the fuel lines running from the engine to the chassis (see Chapter 4). Plug or cap all open fittings/lines.

10 Disconnect the throttle linkage (and TV linkagelcruise control cable, if equipped) from the engine (see Chapter 4).

11 On power steering equipped vehicles, unbolt the power steering pump (see Chapter 10). Leave the lineslhoses attached (see illustration) and make sure the pump is kept in an upright position in the engine compartment (use wire or rope to restrain it out of the way). 12 On air conditioned vehicles, unbolt the compressor (see Chapter 3) and set it aside. Do not disconnect the hoses (see illustration).

13 Drain the engine oil (see Chapter 1) and remove the oil filter.

14 Remove the starter motor (see Chapter 5).

15 Remove the alternator (see Chapter 5).

5.56 Remove the attaching screw and unplug the firewall electrical connector

5.56 Remove the attaching screw and unplug the firewall
electrical connector

16 Unbolt the exhaust system from the engine (see Chapter 4).

17 If you’re working on a vehicle with an automatic transmission, refer to Chapter 7 and remove the torque converter-to-driveplate fasteners.

18 Support the transmission with a jack. Position a block of wood between the jack and transmission to prevent damage to the transmission. Special transmission jacks with safety chains are available – use one if possible.

19 Attach an engine sling or a length of chain to the lifting brackets on the engine.

5.5~ Remove the nut on the engine stud and disconnect the ground strap (arrow)

5.5~ Remove the nut on the engine stud and disconnect
the ground strap (arrow)

20 Roll the hoist into position and connect the sling to it (see illustration). Take up the slack in the sling or chain, but don’t lift the engine. Warning: DO NOTplace any part of your body under the engine when it’s supported only by a hoist or other lifting device.

21 Remove the transmission-to-engine block bolts.

22 Remove the engine mount-to-frame bolts.

23 Recheck to be sure nothing is still connecting the engine to the transmission or vehicle. Disconnect anything still remaining.

24 Raise the engine slightly. Carefully work it forward to separate it from the transmission. If you’re working on a vehicle with an automatic transmission, be sure the torque converter stays in the transmission (clamp a pair of vise-grips to the housing to keep the converter from sliding out). If you’re working on a vehicle with a manual transmission, the input shaft must be completely disengaged from the clutch.

5.1 1 Set the power steering pump aside with the lines still connected - be sure it's upright so fluid won't spill

5.1 1 Set the power steering pump aside with the lines
still connected – be sure it’s upright so fluid won’t spill

5.12 Unbolt the air conditioning compressor and set it out of the way

5.12 Unbolt the air conditioning compressor and set it out
of the way

5.20 Connect the lifting sling to the hoist and take up the slack

5.20 Connect the lifting sling to the hoist and take up the slack

5.24a Pull the engine forward as far as possible to clear the transmission, .

5.24a Pull the engine forward as far as possible to clear
the transmission, .

Slowly raise the engine out of the engine compartment (see illustrations). Check carefully to make sure nothing is hanging up. 25 Remove the flywheelidriveplate and mount the engine on an engine stand.

5.24b . . . then lift the engine high enough to clear the body

5.24b . . . then lift the engine high enough to clear the body


26 Check the engine and transmission mounts. If they’re worn or damaged, replace them.

27 If you’re working on a vehicle with a manual transmission, install the clutch and pressure plate (Chapter 7). Now is a good time to install a new clutch.

28 Carefully lower the engine into the engine compartment – make sure the engine mounts line up.

29 If you’re working on a vehicle with an automatic transmission, guide the torque converter into the crankshaft following the procedure outlined in Chapter 7.

30 If you’re working on a vehicle with a manual transmission, apply a dab of high-temperature grease to the input shaft and guide it into the crankshaft pilot bearing until the bellhousing is flush with the engine block.

31 Install the transmission-to-engine bolts and tighten them securely. Caution: DO NOT use the bolts to force the transmission and engine together!

32 Reinstall the remaining components in the reverse order of removal.

33 Add coolant, oil, power steering and transmission fluid as needed.

34 Run the engine and check for leaks and proper operation of all accessories, then install the hood and test drive the vehicle.

35 Have the air conditioning system recharged and leak tested.

7.3b Inline six-cylinder engine - left side view

7.3b Inline six-cylinder engine – left side view

7.3a lnline six-cylinder engine - front view

7.3a lnline six-cylinder engine – front view

Engine rebuilding alternatives

The do-it-yourselfer is faced with a number of options when performing an engine overhaul. The decision to replace the engine block, pistoniconnecting rod assemblies and crankshaft depends on a number of factors, with the number one consideration being the condition of the block. Other considerations are cost, access to machine shop facilities, parts availability, time required to complete the project and the extent of prior mechanical experience on the part of the do-it-yourselfer.

7.3~ Inline six-cylinder engine - right side view

7.3~ Inline six-cylinder engine – right side view

7.5 Internal engine components - exploded view (inline six-cylinder engine)

7.5 Internal engine components – exploded view
(inline six-cylinder engine)

1 Engine oil dipstick and tube
2 Oil filter b y-pass plug
3 Build date code location
4 Ring set
5 Piston
6 Pin set
7 Plug
8 Engine block
9 Oil channel plug
10 Camshaft
11 Connecting rod
12 Pin
13 Camshaft sprocket
14 Keys
15 Washer
16 Timing chain
17 Oil shedder (slingerl
18 Crankshaft sprocket
19 Crankshaft
20 Connecting rod bearing
21 Connecting rod bearing cap

22 Main bearings
23 Vibration damper pulley
24 Washer
25 Vibration damper
26 Seal
27 Timing chain cover
28 Gasket
29 Main bearing cap (rear)
30 Main bearing cap seal
31 kit (rear)
32 Pilot bushing [with
33 manual transmission)
34 Bushing oil wick (with
35 manual transmission)
36 Flywheel and ring gear
(with manual transmission)
37 Bearing set
38 Dowel
39 Plug

Some of the rebuilding alternatives include:

Individual parts – If the inspection procedures reveal that the engine block and most engine components are in reusable condition, purchasing individual parts may be the most economical alternative. The block, crankshaft and pistonlconnecting rod assemblies should all be inspected carefully. Even if the block shows little wear, the cylinder bores should be surface honed.

Short block – A short block consists of an engine block with a crankshaft, camshaft and pistonlconnecting rod assemblies already installed. All new bearings are incorporated and all clearances will be correct. The existing valve train components, cylinder head(s) and external parts can be bolted to the short block with little or no machine shop work necessary. Long block – A long block consists of a short block plus an oil pump, oil pan, cylinder head(s), rocker arm cover(s) and valve train components, timing sprockets and chain or gears and timing cover. All components are installed with new bearings, seals and gaskets incorporated throughout. The installation of manifolds and external parts is all that’s necessary.

Give careful thought to which alternative is best for you and discuss the situation with local automotive machine shops, auto parts dealers and experienced rebuilders before ordering or purchasing replacement parts.

Engine overhaul – disassembly sequence

Refer to illustrations 7.3a, 7.3b, 7.3~an d 7.5 1 It’s much easier to disassemble and work on the engine if it’s mounted on a portable engine stand. A stand can often be rented quite cheaply from an equipment rental yard. Before the engine is mounted on a stand, the flywheelldriveplate should be removed from the engine.

2 If a stand isn’t available, it’s possible to disassemble the engine with it blocked up on the floor. be extra careful not to tip or drop the engine when working without a stand.

3 If you’re going to obtain a rebuilt engine, all external components must come off first (see illustrations), to be transferred to the replacement engine, just as they will if you’re doing a complete engine overhaul yourself. These include:

Alternator and brackets
Emissions control components
Distributor, spark plug wires and spark plugs
Thermostat and housing cover
Water pump
Fuel injection components or carburetor
lntake/exhaust manifolds
Oil filter
Engine mounts
Clutch and flywheel/driveplate
Engine rear plate

Note: When removing the external components from the engine, pay close attention to details that may be helpful or important during installation. Note the installed position of gaskets, seals, spacers, pins, brackets, washers, bolts and other small items.

4 If you’re obtaining a short block, which consists of the engine block, crankshaft, pistons and connecting rods all assembled, then the cylinder head(s), oil pan and oil pump will have to be removed as well. See Engine rebuilding alternatives for additional information regarding the different possibilities to be considered.

5 If you’re planning a complete overhaul, the engine must be disassembled and the internal components (see illustration) removed in the following order:

Rocker arm coverlsl
Intake and exhaust manifolds
Rocker arms and pushrods
Cylinder headls)
Valve lifters
Timing cover
Timing chain and sprockets
Oil pan
Oil pump
Piston/connecting rod assemblies
Crankshaft and main bearings

6 Before beginning the disassembly and overhaul procedures, make sure the following items are available. Also, refer to Engine overhaul – reassembly sequence for a list of tools and materials needed for engine reassembly.

Common hand tools
Small cardboard boxes or plastic bags for storing parts
Gasket scraper
Ridge reamer
Vibration damper puller
Telescoping gauges
Dial indicator set
Valve spring compressor
Cylinder surfacing hone
Piston ring groove cleaning tool
Electric drill motor
Tap and die set
Wire brushes
Oil gallery brushes
Cleaning solvent

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The relevant information:

Four-cylinder engine
Cylinder compression pressure . 155 to 185 psi
Maximum allowable variation between cylinders 30 psi
Oil pressure
At idle (800 rpm) . 25 to 35 psi
Above 1600 rpm . 37 to 75 psi
Engine block
Cylinder bore diameter (standard) . 3.8751 to 3.8775 in
Maximum allowable taper and out-of-round 0.001 in
Warpage limit. . 0.002 in per 6 inches
Valve lifter bore diameter . 0.9055 to 0.9065 in
Cylinder head and valves
Cylinder head warpage limit . 0.002 in per 6 in (0.006 in overall)
Minimum valve margin . 1132-in
Valve stem diameter. 0.31 1 to 0.31 2 in
Valve stem-to-guide clearance . 0.001 to 0.003 in
Valve spring pressure
Valve closed . 80 to 90 Ibs at 1.64 in
Valve open 200 Ibs at 1.2 16 in
Valve spring free length 1.967 in
Valve spring installed height . Not available
Valve lifter
Diameter. . 0.904 to 0.9045 in
Lifter-to-bore clearance . 0.001 to 0.0025 in

…and more

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