Page Number - 4
Form 824255
eign 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 compres
-
sion 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 dam
-
aged piston rings. If the reading is approximately 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 compres-
sion tester main hose end until the o-ring seats (do not
use a wrench to tighten).
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 cor-
rect 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 in
-
cluded), 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:
For technical questions, please contact our Technical Ser
-
vice Department:
Phone:(314) 679-4200 Ext 4782
Fax: (314) 679-HELP (4357)
E-mail:
Visit our Web Site at:
www.mityvac.com
TO AVOID PERSONAL INJURY AND/OR VEHICLE DAM-
AGE:
While some precautions are specified in this manual,
and should be noted to avoid personal injury or vehicle
