ENGINE TUNE-UP PROCEDURES
T h e tune-up procedures apply to the individual
There is no scheduled interval for performing an
engines of multiple engine units as well as to the single
engine tune up. As long as the engine performance is
engine units. However, the throttle linkage of multiple
satisfactory. no tune-up should be needed Minor
engine units must he adjusted after the individual
adjustments in t h e valve and injector operating
engines have been tuned up.
mechanisms. governor, etc. should only he required
periodically to compensate for normal wear on parts.
Four types of governors are used. Since each governor
Tune- Up Sequence for Mechanical Governors
has different characteristics, the tune-up procedure
varies accordingly. The four types are:
CAUTION: Before starting an engine after an
engine speed control adjustment or after
1. Limiting speed mechanical.
removal of the engine governor cover. the
serviceman must determine that the injector
2. Variable speed mechanical.
racks move to the no-fuel position when the
g o v e r n o r stop lever is placed in the stop
3. Variable speed hydraulic.
position. Engine overspeed will result if the
Injector racks cannot be positioned at no-fuel
4. Limiting speed hydraulic.
with the governor stop lever.
The mechanical engine governors are identified by a
1. Adjust the exhaust valve clearance.
name plate attached to the governor housing. The
letters D.W. L.S. stamped on the name plate denote
2. Time the fuel injectors.
a double-weight limiting speed governor. A single--
weight variable speed governor name plate is stamped
3. Adjust the governor gap.
S.W.-V.S.
4. Position the injector rack control levers.
Normally, when performing a tune-up on an engine
in service, it is only necessary to check the various
5. Adjust the maximum no-load speed.
adjustments for a possible change in the settings.
However, if the cylinder head, governor or injectors
6. Adjust the idle speed.
h a v e been replaced or overhauled, then certain
preliminary a d j u s t m e n t s are required before the
7. Adjust the buffer screw.
engine is started.
8. Adjust the throttle booster spring (variable speed
governor only).
The preliminary adjustments consist of the first four
items in the tune-up sequence. The procedures are the
9. Adjust the supplementary governing device (if
same except that the valve clearance is greater for a
used).
cold engine.
To tune-up an engine completely, all of the
Tune-Up Sequence for Hydraulic Governor
adjustments, except the valve bridge adjustment on
four valve cylinder heads, are made by following the
1. Adjust the exhaust valve clearance.
applicable tune-up sequence given below, after the
engine has reached normal operating temperature.
2. Time the fuel injectors.
Since the adjustments are normally made while the
engine is stopped, it may be necessary to run the
3. Adjust the governor linkage.
e n g i n e between adjustments to maintain normal
operating temperature.
4. Position the injector rack control levers.
NOTE: The exhaust valve bridges on the four
5. Adjust the load limit screw.
valve cylinder head are adjusted at the time the
cylinder head is installed on the engine and,
6. Compensation adjustment (PSG governors only).
until wear occurs, no further adjustment is
required. When wear is evident, perform a
7. Adjust the governor speed droop.
complete valve bridge adjustment as outlined
8. Adjust the maximum no-load speed.
on the following pages.
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