Yanmar 1GM User Manual page 63

OPERATION, LUBRICATION, MAINTENANCE AND TUNE-UP
BATTERY CUTAWAY VIEW
57
~ Hydrometer
Read with
hydrometer level
ENGINE TUNE-UP
A smooth-running, dependable marine engine is more
than a convenience. At sea, it can be the difference be-
tween life and death. To keep the engine running right,
follow a regular program of preventive maintenance.
Part of any preventive maintenance program is a thor-
ough engine tune-up. A tune-up is a series of adjustments
necessary to restore and maintain maximum power and
performance.
Perform an engine tune-up as needed at periodic inter-
vals to maintain maximum engine performance. If the en-
gine is used infrequently, perform a tune-up at least once a
season.
A tune-up consists of the following:
1. Compression test.
2. Valve adjustment.
3. Idle speed adjustment.
Careful and accurate adjustment is crucial to a success-
ful engine tune-up. Each procedure in this section must be
performed exactly as described and in the order presented.
NOTE
Some engine settings, such as maximum en-
gine speed and torque level, are controlled
by adjusting screws in the governor assem-
bly. These adjusting screws are set by the
manufacturer and secured by a lockwire to
prevent unauthorized adjustment. Adjust-
ment of these screws should be performed
only by trained personnel. Detaching a
lockwire may void the engine warranty. Im-
proper adjustment can cause engine dam-
age.
Compression Test
Check the compression of each cylinder as the first step
in a tune-up. A compression test measures the compres-
sion pressure at the end of the compression stroke. Its re-
sults can be used to assess general cylinder and valve