GM Storm/Spectrum 1985-1993 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 section also is a guide to accepted 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 still 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:

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 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 guide before substituting another tool.


Procedures and specifications are given in this section 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. A 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 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 to hot-tanking.

Always coat threads lightly with engine oil or anti-seize compounds before installation, to prevent seizure.

Never over-torque 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 in frictional contact must be pre-lubed to provide lubrication at initial startup. Any product specifically formulated for this purpose can be used, but engine oil is not recommended as a pre-lube.

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 through 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 pre-wound 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 Coarse and Metric Fine thread sizes and a spark plug 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 pre-wound 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 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 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 shown in the illustrations.

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Fig. Fig. 1: Damaged bolt hole threads can be replaced with repair thread inserts

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Fig. Fig. 2: Standard thread repair insert (left), and spark plug thread insert

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Fig. Fig. 3: Drill out the damaged threads using the specified size drill. Drill completely through the hole or to the bottom of a blind hole

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Fig. Fig. 4: Using the tap supplied, tap the hole to receive the thread insert. Keep the tap well oiled and back it out frequently to avoid clogging the threads

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Fig. Fig. 5: Screw the threaded insert onto the installer tool until the tang engages the slot. Screw the insert into the tapped hole until it is 1/4 or 1/2 turn below the top surface. After installation break off the tang using a hammer and punch


See Figure 6

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 wear. Worn piston rings, scored or worn cylinder inserts, 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 earlier, a screw-in type compression gauge is more accurate than 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. Check engine compression as follows:

  1. Warm up the engine to normal operating temperature, the stop the engine and turn the ignition OFF .
  3. Blow dirt from the top of the rocker/camshaft cover to protect the combustion chambers, then remove all spark plugs.
  5. Disconnect the wiring harness and connectors from the distributor.
  7. For the Storm, unplug the cold start injector and fuel injector connections.
  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 clutch pedal fully, if equipped with a manual transaxle (this will lighted the engine load) and depress the accelerator pedal fully (to the wide open throttle position). 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 to the reading in each cylinder.
  5. A cylinder's compression pressure is usually acceptable if it is not less than 80% of the highest reading. For example, if the highest reading is 150 psi, the lowest should be no lower than 120 psi. No cylinder should have a reading below 100 psi. The Spectrum engines should show readings of 128-179 psi (883-1226 kPa). The Storm 1.6L engine should have compression pressure of about 142-191 psi (979-1317 kPa) while the 1.8L engine should read about 170 psi (1177 kPa).
  7. 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 is likely that the cylinder's piston rings and/or insert 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.

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Fig. Fig. 6: For the Storm, be sure the cold start injector and all of the fuel injector connectors are removed before checking compression - 1.8L engine shown (1.6L engine similar)