TM 5-3820-245-14&P
SECTION VI
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.
The mechanical engine governors are identified by a nameplate attached to the governor housing.
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, perform all of the adjustments in the applicable tune-up sequence given below after the
engine has reached 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.
Use a new valve rocker cover gasket(s) after the tune-up is completed.
Tune-Up Sequence for Mechanical Governor
NOTE: Before starting an engine after an engine speed control adjustment or after removal of the engine
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).
PAGE 168
