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9. Crank engine several times to ensure removal of any
foreign matter that may have fallen into the cylinders
during preparation 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 test on each cylinder. If any of the cylinder
readings are found to be low or uneven, perform wet
compression test.
15. When compression test is complete, return the
spark plugs to their respective cylinders and the
throttle and ignition components to their normal
positions.
Wet Compression Test Procedure
CAUTION: DO NOT perform the wet compression test
on any diesel engine. The higher compression in a
diesel engine may cause engine damage or injury to
the technician.
The wet compression is a way to remove the influence of
the piston rings, pistons and cylinders from the com-
pression test. After completing the dry compression test,
squirt approximately one teaspoon of engine oil into the
spark plug holes and crank the engine several times to
seal the piston rings. Repeat the dry compression test
outlined above. NOTE: If the readings during the wet
compression test are greater, then air is leaking around
worn or damaged piston rings. If the reading is approxi-
mately the same for both wet and dry tests then the
valves, valve lifters or the camshaft lobes are worn. Any
low reading of cylinder compression indicates worn or
damaged parts.
Small Engine Compression Testing
The Mityvac Professional Compression Test Kit has two
(2) adapters, 10mm and 12mm, that allow it to be used
on small engines found in lawn mowers, chain saws
and line trimmers. To use these adapters:
1. Disconnect the spark plug wire and remove the spark
plug.
2. Thread the appropriate size adapter onto the com-
pression tester main hose end until the o-ring seats
(do not use a wrench to tighten).
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3. Thread the assembly into the cylinder spark plug hole
until the o-ring on the adapter seats firmly (do not use
a wrench to tighten).
4. Ensure the spark plug is grounded to the cylinder
head or is insulated in a way that will prevent an
electric shock hazard.
5. Crank the engine over using the pull cord (or starter if
electric) a minimum of 5 revolutions. This will allow
the cylinder to build sufficient compression to be
measured.
6. Refer to the manufacturer's data to determine the
correct reading
Using the Pressure Hold Adapter
The Mityvac Professional Compression Tester comes
with a pressure hold adapter. This adapter is used to
perform valve seal replacement on an engine without
removing the cylinder head(s). To use the adapter:
1. Remove the spark plug from the desired cylinder.
2. Select the appropriate extension hose that will fit the
spark plug hole.
3. Using the valve core tool (from the field service kit
included), remove the valve core from the end of the
hose and lay it aside.
4. Thread the extension hose into the spark plug hole
until the o-ring seats; do not use pliers or a wrench to
tighten.
5. Attach the Air Hold Adapter to the extension hose.
6. Attach a shop air hose to the Air Hold Adapter, this will
maintain air pressure in the cylinder to hold the
valves closed while performing repairs. (It may be
necessary to rotate the engine until all valve are
closed and air is holding in the cylinder)
Note: Air Hold quick connector does not come with a
compressed air line fitting to adapt to your air source.
This will have to be purchased separately to fit your
system.
Contacting Lincoln Industrial Corp.
Lincoln Industrial Corporation,
One Lincoln Way,
St. Louis, MO 63120
Phone: (314) 679-4200 Ext. 4410
Fax: (800) 424-5359
E-mail: custserv@lincolnindustrial.com
For technical questions, please contact our Technical
Service Department:
Phone:(314) 679-4200 Ext 4782
Fax: (314) 679-HELP (4357)
E-mail: techserv@lincolnindustrial.com
Visit our Web Site at: www.mityvac.com
Form 823541
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