Jeep CJ/Scrambler 1971-1986 Repair Guide

Engine Overhaul Tips


Most engine overhaul procedures are fairly standard. In addition to specific parts replacement procedures and complete specifications for your individual engine, this information also is a guide to accept rebuilding procedures. Examples of standard rebuilding practice are shown and should be used along with specific details concerning 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.

On the other hand, much of the rebuilding work (crankshaft, block, bearings, piston rods, and other components) is well within the scope of the do-it-yourself mechanic.


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 mechanic's tool kit (see General Information & Maintenance ). More in-depth work will require any 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
Valve spring compressor
Ring groove cleaner
Piston ring expander and compressor
Ridge reamer
Cylinder hone or glaze breaker
Engine stand

The use of most of these tools is illustrated in this information. 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 Safety Notice in the front of this guide before substituting another tool.


Procedures and specifications are given in this information for inspecting, cleaning and assessing the wear limits of most major components. Other procedures such as Magnaflux® and Zyglo® can be used to locate material flaws and stress cracks. Magnaflux® is a magnetic process applicable only to ferrous materials. The Zyglo® process coats the material with a fluorescent dye penetrant and can be used on any material Check for suspected surface cracks can be more readily made using spot check dye. The dye is sprayed onto the suspected area, wiped off and the area sprayed with a developer. Cracks will show up brightly.


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 the tanking.
Always coat threads lightly with engine oil or antiseize compounds before installation, to prevent seizure.
Never overtorque bolts or spark plugs especially in aluminum threads.

Stripped threads in any component can be repaired using any of several commercial repair kits (Heli-Coil®, Microdot®, Keenserts®, etc.).

When assembling the engine, any parts that will be 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.

When semi-permanent (locked, but removable) installation of bolts or nuts is desired, threads should be cleaned and coated with Loctite® or other similar, commercial non-hardening sealant.


See Figures 1, 2, 3, 4 and 5

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 manufacturer's 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 information. 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 effecting a repair to 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 be removed with locking pliers or with a screw or stud extractor. After the hole is clear, the thread can be repaired, as follows:

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Fig. Fig. 1: Damaged bolt holes can be repaired with thread repair inserts

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Fig. Fig. 2: Standard thread repair insert on the left and a spark plug type on the right

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Fig. Fig. 3: Drill out the damaged threads with the correct size drill. Drill completely through the hole or to the bottom of the blind hole

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Fig. Fig. 4: With the tap supplied in the repair kit, tap the hole to receive the repair insert. Keep the tap well oiled and back it out often to avoid clogging the threads

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Fig. Fig. 5: Screw the insert onto the installation tool until the tang engages the slot. Screw the insert into the tapped hole until it is just below the top surface. After installation, break the tang off with a hammer and punch

Checking Engine Compression

A noticeable lack of engine power, excessive oil consumption and/or poor fuel mileage measured over an extended period are all indicators of internal engine war. Worn piston rings, scored or worn cylinder bores, blown head gaskets, sticking or burnt valves and worn valve seats are all possible culprits here. A check of each cylinder's compression will help you locate the problems.

As mentioned in the Tools and Equipment information of General Information & Maintenance , a screw-in type compression gauge is more accurate that the type you simply hold against the spark plug hole, although it takes slightly longer to use. It's worth it to obtain a more accurate reading. Follow the procedures below.

  1. Warm up the engine to normal operating temperature.
  3. Remove all spark plugs.
  5. Disconnect the high tension lead from the ignition coil.
  7. On fully open the throttle either by operating the carburetor throttle linkage by hand or by having an assistant floor the accelerator pedal.
  9. Screw the compression gauge into the no.1 spark plug hole until the fitting is snug.

Be careful not to crossthread the plug hole. On aluminum cylinder heads use extra care, as the threads in these heads are easily ruined.

  1. Ask an assistant to depress the accelerator pedal fully on both carbureted and fuel injected Jeep vehicles. Then, while you read the compression gauge, ask the assistant to crank the engine two or three times in short bursts using the ignition switch.
  3. Read the compression gauge at the end of each series of cranks, and record the highest of these readings. Repeat this procedure for each of the engine's cylinders. Compare the highest reading of each cylinder to the compression pressure specification in the Tune-Up Specifications chart in Engine Performance & Tune-up . The specs in this chart are maximum values.

A cylinder's compression pressure is usually acceptable if it is not less than 80% of maximum. The difference between any two cylinders should be no more than 12-14 pounds.

  1. If a cylinder is unusually low, pour a tablespoon of clean engine oil into the cylinder through the spark plug hole and repeat the compression test. If the compression comes up after adding the oil, it appears that the cylinder's piston rings or bore are damaged or worn. If the pressure remains low, the valves may not be seating properly (a valve job is needed), or the head gasket may be blown near that cylinder. If compression in any two adjacent cylinders is low, and if the addition of oil doesn't help the compression, there is leakage past the head gasket. Oil and coolant water in the combustion chamber can result from this problem. There may be evidence of water droplets on the engine dipstick when a head gasket has blown.