Compression Testing - Honda Motorcycle Service Manual

ENGINE TESTING
COMPRESSION TESTING
GENERAL
A compression test is a quick and easy way t o check the general condition of an engine. This test should be performed prior to
any tune-up work, especially if the machine did not come in under its own power. If the engine has a burnt valve for instance,
the customer should be notified that the tune-up will have no benefit without the other necessary engine work. A compres-
sion test should also be done if you feel that the motorcycle, scooter or ATV lacks power, especially during acceleration.
A compression test can be inconclusive though, if the engine is not completely stock, if the bettery is not in perfect condition
(in electric-start models, engine cranking speed may be low) or i f t h e test instructions are not followed completely. In each of
these situations, the compression registered will be lower than the service limit in the Model Specific service manual.
When you do get a valid compression test, there is something else to consider.
What if the compression is below the service limit, or if the compression is relatively even between each cylinder, and the
engine is not smoking
?
There may be no reason for
an
expensive rebuild on
a
good running engine. If, on the other hand,the
compression on any one cylinder in a twin or multi-cylinder engine is significantly lower, the engine must be rebuilt.
TESTING
NOTE
If the motorcycle has a decompressor, be sure it is
adjusted properly before checking compression. On
motorcycles equipped with an automatic demcom-
pression starting system, the decompressors must be
deactivated ~ r i o r to checkina
Warm up the engine to normal operating temperature.
Ten minutes of stop and go riding is sufficient.
Stop the engine and remove a spark plug from each cylinder.
Install the compression gauge attachment to the cylinder to be
tested.
Connect the compression gauge
NOTE
.
Make sure that there are no leaks around the attach-
ment.
TOOL:
COMPRESSION GAUGE 0 7 3 0 5 - 0 0 1 0 0 0 0
Kick start models:
Fully open the throttle and choke valves, strongly kick the
starter pedal through several times, and check the
compression.
Electric start models:
Turn the engine stop switch "OFF"
starter motor willnot operate. Remove the spark plug
cap from the spark plug. Using tape or strings, secure
the cap t o any convenient plastic body part. Then turn
the engine stop switch "RUN" and crank the engine with
the starter motor.
Fully open the throttle and choke valves, crank the engine
with the starter motor, and check the compression
COMPRESSION GAUGE
\
\
ATTACHMENT
NOTE
/
To avoid discharning the battery, do not operate the
1
/
electric starter fo[mbre than seven seconds.
1
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Date of Issue : March, 1995
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HONDA MOTOR CO.,LTD.