DETROIT DIESEL
ENGINE TUNE-UP PROCEDURES
There is no scheduled interval for performing an engine tune-up. As long as the engine performance is satisfactory, no
tune-up should be needed. Minor adjustments in the valve and injector operating mechanisms, governor, etc. should
only be required periodically to compensate for normal wear on parts. Three types of governors are used. Since each
governor has different characteristics, the tune-up procedure varies accordingly. The three types are:
1. Limiting speed mechanical.
2. Variable speed mechanical.
3. Hydraulic.
The mechanical engine governors are identified by a name plate attached to the governor housing. The letters D.W.-
L.S. stamped on the name plate denote a double-weight limiting speed governor. A single weight variable speed
governor name plate is stamped S.W.-V.S.
Normally, when performing a tune-up on an engine in service, it is only necessary to check the various adjustments for a
possible change in the settings. However, if the cylinder head, governor or injectors have been replaced or overhauled,
then certain preliminary adjustments are required before the engine is started.
The preliminary adjustments consist of the first four items in the tune-up sequence. The procedures are the same except
that the valve clearance is greater for a cold engine.
To tune-up an engine completely, all of the adjustments are made by following the applicable tune-up sequence given
below after the engine has reached the normal operating temperature. Since the adjustments are normally made while
the engine is stopped, it may be necessary to run the engine between adjustments to maintain normal operating
temperature.
Tune-Up Sequence for Mechanical Governor
Before starting an engine after an engine speed control adjustment or after removal of the engine
CAUTION:
governor cover, the serviceman must determine that the injector racks move to the no-fuel position when the
governor stop lever is placed in the stop position. Engine overspeed will result if the injector racks cannot be
positioned at no fuel with the governor stop lever.
1. Adjust the exhaust valve clearance.
2. Time the fuel injectors.
3. Adjust the governor gap.
4. Position the injector rack control levers.
5. Adjust the maximum no-load speed.
6. Adjust the idle speed.
7. Adjust the buffer screw.
8. Adjust the throttle booster spring (variable speed governor only).
9. Adjust the supplementary governing device (if used).
Tune-Up Sequence for Hydraulic Governor
1. Adjust the exhaust valve clearance.
2. Time the fuel injectors.
3. Adjust the fuel rod.
4. Position the injector rack control levers.
5. Adjust the load limit screw.
6. Adjust the speed droop.
7. Adjust the maximum no-load speed.
NOTE: Use new valve rocker cover gasket(s)
after each tune-up.
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