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Tools:
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Engine
compression gauge
and what
ever other tools you need to remove spark plugs.
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This is great
a way to find if you engine is loosing power, burning oil or it needs
a new head gasket.
Note:
Always use a fully charged battery to obtain specific engine revolution.
INSTRUCTIONS
Test Procedure
1. Warm up engine. Run the engine for about ten minutes or until
it reaches normal operating temperature before performing the compression
test.
2. Stop the engine.
3. Loosen all spark plugs about one turn, but do not remove them.
Use an air hose or stiff brush to remove all the dirt from the spark
plug wells. Remove the spark.
4. Set the carburetor throttle plates to the wide open throttle
position using a string or wire. Or depress accelerator pedal fully
to keep throttle valve wide open.
5. Disconnect distributor center cable and connect to ground
(jumper cables).This prevents possible sparks.
6. Screw the spark plug adapter hose into a spark plug well.
Hand tighten only.
8. Crank the engine for at least four compression strokes or
until the pressure reading stops rising on the gauge.
9. Record the compression reading.
10. Repeat steps 6 through 10 for the remainder of the cylinders
to be tested.
Test Results
1. On a normal cylinder, the gauge needle should travel up-scale
on each compression stroke until it reaches a peak value. All cylinders
should indicate a pressure that is within the vehicle manufacturer's
specifications, and the reading should not vary more than 10% from cylinder
to cylinder.
2. If the needle fails to travel upscale as described in Step
1, or if it remains at the same value for several strokes and then starts
to climb, the cylinder has a sticking valve.
3. If the compression reading is considerably higher than the
vehicle manufacturer's specification, it indicates carbon buildup in
the cylinder.
4. If a reading on two adjacent cylinders is 20 pounds (or more)
lower than the other cylinders, a defective head gasket is indicated.
Water (coolant) and/or oil may be found in the two cylinders under these
conditions.
5. If the
readings are low or vary widely between cylinders, pour a teaspoon of
clear S.A.E. grade 30 oil into each cylinder through the spark plug
hole and re-test.
* If the readings
increase considerably, the fault may be due to poorly seated or worn
piston rings.
* If the readings remain about the same, the valves and/or associated
components are likely the cause.
6. Clean,
regap and reinstall the spark plugs in the same order in which they
were removed, or install new spark plugs. Reconnect all spark plug wires
in the proper order. Remove the string or wire from the carburetor throttle
plates and make certain it returns to closed throttle position.
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