1991 1999 ford explorer chilton User Manual

							With the engine cold, locate and remove the oil pressure sending unit.
1. 
Following the manufacturers instructions, connect a mechanical oil pressure gauge and, if necessary,
a tachometer to the engine.
2. 
Start the engine and allow it to idle.
3. 
Check the oil pressure reading when cold and record the number. You may need to run the engine at a
specified rpm, so check the specifications.
4. 
Run the engine until normal operating temperature is reached (upper radiator hose will feel warm).
5. 
Check the oil pressure reading again with the engine hot and record the number. Turn the engine
OFF.
6. 
Compare your hot oil pressure reading to specification. If the reading is low, check the cold pressure
reading against the chart. If the cold pressure is well above the specification, and the hot reading was
lower than the specification, you may have the wrong viscosity oil in the engine. Change the oil,
making sure to use the proper grade and quantity, then repeat the test.
7. 
Low oil pressure readings could be attributed to internal component wear, pump related problems, a low oil
level, or oil viscosity that is too low. High oil pressure readings could be caused by an overfilled crankcase,
too high of an oil viscosity or a faulty pressure relief valve.
Buy or Rebuild?
Now if you have determined that your engine is worn out, you must make some decisions. The question of
whether or not an engine is worth rebuilding is largely a subjective matter and one of personal worth. Is the
engine a popular one, or is it an obsolete model? Are parts available? Will it get acceptable gas mileage once
it is rebuilt? Is the car its being put into worth keeping? Would it be less expensive to buy a new engine, have
your engine rebuilt by a pro, rebuild it yourself or buy a used engine from a salvage yard? Or would it be
simpler and less expensive to buy another car? If you have considered all these matters, and have still decided
to rebuild the engine, then it is time to decide how you will rebuild it.
The editors at Chilton feel that most engine machining should be performed by a professional machine
shop. Think of it as an assurance that the job has been done right the first time. There are many
expensive and specialized tools required to perform such tasks as boring and honing an engine block or
having a valve job done on a cylinder head. Even inspecting the parts requires expensive micrometers
and gauges to properly measure wear and clearances. A machine shop can deliver to you clean, and
ready to assemble parts, saving you time and aggravation. Your maximum savings will come from
performing the removal, disassembly, assembly and installation of the engine and purchasing or renting
only the tools required to perform these tasks.
A complete rebuild or overhaul of an engine involves replacing all of the moving parts (pistons, rods,
crankshaft, camshaft, etc.) with new ones and machining the non-moving wearing surfaces of the block and
heads. Unfortunately, this may not be cost effective. For instance, your crankshaft may have been damaged or
worn, but it can be machined undersize for a minimal fee.
So although you can replace everything inside the engine, it is usually wiser to replace only those parts which
are really needed, and, if possible, repair the more expensive ones. Later in this section, we will break the
engine down into its two main components: the cylinder head and the engine block. We will discuss each
component, and the recommended parts to replace during a rebuild on each.
Engine Overhaul Tips
Most engine overhaul procedures are fairly standard. In addition to specific parts replacement procedures and
specifications for your individual engine, this section is also a guide to acceptable rebuilding procedures.
Examples of standard rebuilding practice are given and should be used along with specific details concerning HOW TO USE THIS BOOK
OIL PRESSURE TEST 445 
						

							
your particular engine.
Competent and accurate machine shop services will ensure maximum performance, reliability and engine life.
In most instances it is more profitable for the do-it-yourself mechanic to remove, clean and inspect the
component, buy the necessary parts and deliver these to a shop for actual machine work.
Much of the assembly work (crankshaft, bearings, piston rods, and other components) is well within the scope
of the do-it-yourself mechanics tools and abilities. You will have to decide for yourself the depth of
involvement you desire in an engine repair or rebuild.
TOOLS
The tools required for an engine overhaul or parts replacement will depend on the depth of your involvement.
With a few exceptions, they will be the tools found in a mechanics tool kit (see Section 1 of this manual).
More in-depth work will require some or all of the following:
A dial indicator (reading in thousandths) mounted on a universal base
· 
Micrometers and telescope gauges
· 
Jaw and screw-type pullers
· 
Scraper
· 
Valve spring compressor
· 
Ring groove cleaner
· 
Piston ring expander and compressor
· 
Ridge reamer
· 
Cylinder hone or glaze breaker
· 
Plastigage®
· 
Engine stand
· 
The use of most of these tools is illustrated in this section. Many can be rented for a one-time use from a local
parts jobber or tool supply house specializing in automotive work.
Occasionally, the use of special tools is called for. See the information on Special Tools and the Safety Notice
in the front of this book before substituting another tool.
OVERHAUL TIPS
Aluminum has become extremely popular for use in engines, due to its low weight. Observe the following
precautions when handling aluminum parts:
Never hot tank aluminum parts (the caustic hot tank solution will eat the aluminum.)
· 
Remove all aluminum parts (identification tag, etc.) from engine parts prior to the tanking.
· 
Always coat threads lightly with engine oil or anti-seize compounds before installation, to prevent
seizure.
· 
Never overtighten bolts or spark plugs especially in aluminum threads.
· 
When assembling the engine, any parts that will be exposed to frictional contact must be prelubed to provide
lubrication at initial start-up. Any product specifically formulated for this purpose can be used, but engine oil
is not recommended as a prelube in most cases.
When semi-permanent (locked, but removable) installation of bolts or nuts is desired, threads should be
cleaned and coated with Loctite® or another similar, commercial non-hardening sealant. HOW TO USE THIS BOOK
446 Engine Overhaul Tips 
						

							
CLEANING
Before the engine and its components are inspected, they must be thoroughly cleaned. You will need to
remove any engine varnish, oil sludge and/or carbon deposits from all of the components to insure an accurate
inspection. A crack in the engine block or cylinder head can easily become overlooked if hidden by a layer of
sludge or carbon.
Use a gasket scraper to remove the old gasket material from the mating surfaces
Most of the cleaning process can be carried out with common hand tools and readily available solvents or
solutions. Carbon deposits can be chipped away using a hammer and a hard wooden chisel. Old gasket
material and varnish or sludge can usually be removed using a scraper and/or cleaning solvent. Extremely
stubborn deposits may require the use of a power drill with a wire brush. If using a wire brush, use extreme
care around any critical machined surfaces (such as the gasket surfaces, bearing saddles, cylinder bores, etc.).
Use of a wire brush is NOT RECOMMENDED on any aluminum components. Always follow any safety
recommendations given by the manufacturer of the tool and/or solvent.
CAUTION
Always wear eye protection during any cleaning process involving scraping, chipping or spraying of solvents.
An alternative to the mess and hassle of cleaning the parts yourself is to drop them off at a local garage or
machine shop. They should have the necessary equipment to properly clean all of the parts for a nominal fee. HOW TO USE THIS BOOK
CLEANING 447 
						

							Before cleaning and inspection, use a ring expander tool to remove the piston rings
Remove any oil galley plugs, freeze plugs and/or pressed-in bearings and carefully wash and degrease all of
the engine components including the fasteners and bolts. Small parts such as the valves, springs, etc., should
be placed in a metal basket and allowed to soak. Use pipe cleaner type brushes, and clean all passageways in
the components.
Use a ring expander and remove the rings from the pistons. Clean the piston ring grooves with a special tool
or a piece of broken ring. Scrape the carbon off of the top of the piston. You should never use a wire brush on
the pistons. After preparing all of the piston assemblies in this manner, wash and degrease them again.
Clean the piston ring grooves using a ring groove cleaner tool, or ...HOW TO USE THIS BOOK
448 CLEANING 
						

							... use a piece of an old ring to clean the grooves. Be careful, the ring can be quite sharp
WARNING
Use extreme care when cleaning around the cylinder head valve seats. A mistake or slip may cost you a new
seat.
When cleaning the cylinder head, remove carbon from the combustion chamber with the valves installed. This
will avoid damaging the valve seats.
REPAIRING DAMAGED THREADS
Damaged bolt hole threads can be replaced with thread repair insertsHOW TO USE THIS BOOK
REPAIRING DAMAGED THREADS 449 
						

							Standard thread repair insert (left), and spark plug thread insert
Drill out the damaged threads with the specified size bit. Be sure to drill completely through the hole or to the bottom of a blind hole
Using the kit, tap the hole in order to receive the thread insert. Keep the tap well oiled and back it out frequently to avoid clogging the threadsHOW TO USE THIS BOOK
450 REPAIRING DAMAGED THREADS 
						

							Screw the insert onto the installer tool until the tang engages the slot. Thread the insert into the
hole until it is  1
/4 - 1
/2  turn below the top surface, then remove the tool and break off the tang
using a punch
Several methods of repairing damaged threads are available. Heli-Coil® (shown here), Keenserts® and
Microdot® are among the most widely used. All involve basically the same principle-drilling out stripped
threads, tapping the hole and installing a prewound insert-making welding, plugging and oversize fasteners
unnecessary.
Two types of thread repair inserts are usually supplied: a standard type for most inch coarse, inch fine, metric
course and metric fine thread sizes and a spark lug type to fit most spark plug port sizes. Consult the
individual tool manufacturers catalog to determine exact applications. Typical thread repair kits will contain a
selection of prewound threaded inserts, a tap (corresponding to the outside diameter threads of the insert) and
an installation tool. Spark plug inserts usually differ because they require a tap equipped with pilot threads and
a combined reamer/tap section. Most manufacturers also supply blister-packed thread repair inserts separately
in addition to a master kit containing a variety of taps and inserts plus installation tools.
Before attempting to repair a threaded hole, remove any snapped, broken or damaged bolts or studs.
Penetrating oil can be used to free frozen threads. The offending item can usually be removed with locking
pliers or using a screw/stud extractor. After the hole is clear, the thread can be repaired as shown in the kit
manufacturers instructions.
Engine Preparation
To properly rebuild an engine, you must first remove it from the vehicle, then disassemble and diagnose it.
Ideally you should place your engine on an engine stand. This affords you the best access to the engine
components. Remove the flywheel or flexplate before installing the engine to the stand.
Now that you have the engine on a stand, and assuming that you have drained the oil and coolant from the
engine, its time to strip it of all but the necessary components. Before you start disassembling the engine, you HOW TO USE THIS BOOK
Engine Preparation 451 
						

							
may want to take a moment to draw some pictures, or fabricate some labels or containers to mark the locations
of various components and the bolts and/or studs which fasten them. Modern day engines use a lot of little
brackets and clips which hold wiring harnesses and such, and these holders are often mounted on studs and/or
bolts that can be easily mixed up. The manufacturer spent a lot of time and money designing your vehicle, and
they wouldnt have wasted any of it by haphazardly placing brackets, clips or fasteners on the vehicle. If its
present when you disassemble it, put it back when you assemble, you will regret not remembering that little
bracket which holds a wire harness out of the path of a rotating part.
You should begin by unbolting any accessories still attached to the engine, such as the water pump, power
steering pump, alternator, etc. Then, unfasten any manifolds (intake or exhaust) which were not removed
during the engine removal procedure. Finally, remove any covers remaining on the engine such as the rocker
arm, front or timing cover and oil pan. Some front covers may require the vibration damper and/or crank
pulley to be removed beforehand. The idea is to reduce the engine to the bare necessities of cylinder head(s),
valve train, engine block, crankshaft, pistons and connecting rods, plus any other in block components such
as oil pumps, balance shafts and auxiliary shafts.
Finally, remove the cylinder head(s) from the engine block and carefully place on a bench. Disassembly
instructions for each component follow later in this section.
Cylinder Head
There are two basic types of cylinder heads used on todays automobiles: the Overhead Valve (OHV) and the
Overhead Camshaft (OHC). The latter can also be broken down into two subgroups: the Single Overhead
Camshaft (SOHC) and the Dual Overhead Camshaft (DOHC). Generally, if there is only a single camshaft on
a head, it is just referred to as an OHC head. Also, an engine with an OHV cylinder head is also known as a
pushrod engine.
Most cylinder heads these days are made of an aluminum alloy due to its light weight, durability and heat
transfer qualities. However, cast iron was the material of choice in the past, and is still used on many vehicles.
Whether made from aluminum or iron, all cylinder heads have valves and seats. Some use two valves per
cylinder, while the more hi-tech engines will utilize a multi-valve configuration using 3, 4 and even 5 valves
per cylinder. When the valve contacts the seat, it does so on precision machined surfaces, which seals the
combustion chamber. All cylinder heads have a valve guide for each valve. The guide centers the valve to the
seat and allows it to move up and down within it. The clearance between the valve and guide can be critical.
Too much clearance and the engine may consume oil, lose vacuum and/or damage the seat. Too little, and the
valve can stick in the guide causing the engine to run poorly if at all, and possibly causing severe damage. The
last component all automotive cylinder heads have are valve springs. The spring holds the valve against its
seat. It also returns the valve to this position when the valve has been opened by the valve train or camshaft.
The spring is fastened to the valve by a retainer and valve locks (sometimes called keepers). Aluminum heads
will also have a valve spring shim to keep the spring from wearing away the aluminum.
An ideal method of rebuilding the cylinder head would involve replacing all of the valves, guides, seats,
springs, etc. with new ones. However, depending on how the engine was maintained, often this is not
necessary. A major cause of valve, guide and seat wear is an improperly tuned engine. An engine that is
running too rich, will often wash the lubricating oil out of the guide with gasoline, causing it to wear rapidly.
Conversely, an engine which is running too lean will place higher combustion temperatures on the valves and
seats allowing them to wear or even burn. Springs fall victim to the driving habits of the individual. A driver
who often runs the engine rpm to the redline will wear out or break the springs faster then one that stays well
below it. Unfortunately, mileage takes it toll on all of the parts. Generally, the valves, guides, springs and
seats in a cylinder head can be machined and re-used, saving you money. However, if a valve is burnt, it may
be wise to replace all of the valves, since they were all operating in the same environment. The same goes for
any other component on the cylinder head. Think of it as an insurance policy against future problems related
to that component. HOW TO USE THIS BOOK
452 Cylinder Head 
						

							
Unfortunately, the only way to find out which components need replacing, is to disassemble and carefully
check each piece. After the cylinder head(s) are disassembled, thoroughly clean all of the components.
DISASSEMBLY
Except the 2.3 and 4.0L SOHC (VIN E) Engines
Before disassembling the cylinder head, you may want to fabricate some containers to hold the various parts,
as some of them can be quite small (such as keepers) and easily lost. Also keeping yourself and the
components organized will aid in assembly and reduce confusion. Where possible, try to maintain a
components original location; this is especially important if there is not going to be any machine work
performed on the components.
If you havent already removed the rocker arms and/or shafts, do so now.
1. 
Position the head so that the springs are easily accessed.
2. 
When removing an OHV valve spring, use a compressor tool to relieve the tension from the retainer
Use a valve spring compressor tool, and relieve spring tension from the retainer.
3. 
Due to engine varnish, the retainer may stick to the valve locks. A gentle tap with a hammer may help
to break it loose. HOW TO USE THIS BOOK
DISASSEMBLY 453 
						

							A small magnet will help in removal of the valve locks
Be careful not to lose the small valve locks (keepers)
Remove the valve locks from the valve tip and/or retainer. A small magnet may help in removing the
locks.
4. 
Lift the valve spring, tool and all, off of the valve stem.
5.  HOW TO USE THIS BOOK
454 DISASSEMBLY