Page Number - 3
Form 823451
Always read instructions carefully prior to use.
Included in this Kit
•
Heavy duty 2 ¾” (70 mm) gauge with high impact lens,
rubber boot, and three (3) scales of measure (psi, kg/cm
2
,
bar), attached to 10" (250 mm) hose and quick release
coupler
•
Four (4) extension hoses:
•
6 ½” (165 mm) long x 14 mm thread, short
•
12" (305 mm) long x 14 mm thread, short
•
12" (305 mm) long x 14 mm thread, long
•
12" (305 mm) long x 18 mm thread, short
•
One (1) adapter: 14 mm thread, short x 18 mm thread, long
•
Two (2) small engine adapters
•
10 mm thread
•
12 mm thread
•
One (1) quick release air hold adapter
•
Custom blow-molded case
•
Field service kit
Applications
The Craftsman Professional Compression Test Kit can perform
dry or wet compression tests to determine the amount of
pressure produced in the cylinder of an engine. It can also be
used as a tool for pressurizing an engine cylinder to hold the
valves closed while performing repairs.
How to Perform a Comression Test
Precautions & Diagnostic Notes:
WARNING: DO NOT use the ignition switch during the
compression test on fuel-injected vehicles. Use of a
remote starter switch to crank the engine is recom-
mended. Fuel injectors on many late model vehicles
are triggered by the ignition switch during the cranking
mode, this could result in a fire hazard or contamination
of the engine’s oil with fuel.
Always use eye protection when performing compres-
sion tests.
An engine in good operating condition will produce a certain
amount of pressure in each cylinder. Normally, the cylinders
should be within 10 percentage points of one another and
within the manufacturer’s specifications. The pressure should
rise smoothly on each stroke of the engine, until it reaches a
peak.
If the pressure reading fails to rise, or it remains the same for
several strokes of the engine and begins to rise, the likely
cause of the problem is a sticking valve.
If two adjacent cylinders show pressure readings of 20 or
more pounds below the other cylinder readings, suspect a
blown head gasket.
If a cylinder shows a pressure reading of 15 or more pounds
higher than the other cylinders, the probable cause is carbon
build-up inside the cylinder.
The Craftsman Professional Compression Test Kit can perform
two tests: the dry compression test and the wet compression
test. The result of performing these tests will provide an
indication of the condition of the piston rings, the cylinders, and
valve-train.
Dry Compression Test Procedures:
1. Refer to the appropriate service manual for the compression
specifications specific to the engine you are testing.
2. Start engine and allow engine to run until it reaches normal
operating temperature (usually about 15 minutes.) Turn
engine OFF.
3. Install an auxiliary starter switch in the starting circuit.
4. While wearing eye protection, use compressed air to
carefully remove dirt and debris from the area around the
spark plugs.
5. Remove spark plugs one at a time, marking the number of
the cylinder they were removed from, and place them on a
clean flat surface. This will aid you in identifying problem
cylinders by allowing the comparison of spark plug appear-
ance to the compression level of a given cylinder.
NOTE: When testing engines with two spark plugs per
cylinder, it is only necessary to remove the spark
plugs located on the exhaust side.
6. On vehicles with standard distributors, disconnect the coil
wire (high tension lead) from the distributor cap and secure
it to a suitable ground, or disable the ignition by disconnect-
ing the positive (BAT) terminal from the ignition coil.
7. On vehicles with a distributorless ignition (DIS), disable the
ignition system by removing the electronic ignition (control)
module fuse, or disconnect the crank angle sensor.
NOTE: Refer to the appropriate service manual to
determine which fuse or component to temporarily
remove or disconnect.
8. Remove air cleaner from carburetor or throttle body and
secure throttle linkage in wide-open throttle (WOT) position.
NOTE: NEVER place anything inside the throttle body;
internal damage to the engine could result. On
vehicles equipped with port fuel injection, remove
throttle linkage covers (as necessary) and secure
throttle linkage in the wide-open throttle (WOT)
position.
9. Crank engine several times to ensure removal of any foreign
matter that may have fallen into the cylinders during prepara-
tion for test.
10. Select the appropriate adapter fitting (14mm, 18mm short
reach or 14mm, 18mm long-reach), and thread adapter into
spark plug hole of cylinder head.
11. Connect the appropriate test hose or adapter to the gauge
assembly.
12. Crank the engine at least five compression strokes or until
the pressure reading stops increasing on gauge.
13. Read the pressure level on the gauge and record the
reading along with the cylinder number being tested.
Example: #1-150 psi, #2-145 psi, etc.
14. Repeat this t
est on each cylinder. If any of the cylinder
readings are found to be low or uneven, perform wet
compression test.
