Engine Tune-Up
DETROIT DIESEL
3. Stop the engine and, if necessary, adjust the no-load
avoid contact with the differential lever, turn the idle
speed as follows:
speed adjusting screw (Fig. 8) until the engine is
o p e r a t i n g at approximately 15 rpm below the
a. Remove the high-speed spring retainer with tool
recommended idle speed.
J 5895 and withdraw the high-speed spring and
plunger assembly.
NOTE: The recommended idle speed for non-
EPA certified engines is 500-600 rpm, but may
CAUTION: To prevent the low-speed spring and
vary with special engine applications.
cap from dropping into the governor, be careful
not to jar the assembly while it is being
I f the engine h a s a tendency to stall during
removed.
deceleration, install a new buffer screw. The current
buffer screw uses a heavier spring and restricts the
b. Remove the high-speed spring from the high-
travel of the differential lever to the off (no-fuel)
speed spring plunger and add or remove shims as
position.
required to establish the desired engine no-load
speed.
2. Hold the idle screw and tighten the lock nut.
NOTE: For each .010" in shims added, the
3. Install the high-speed spring retainer cover and
engine speed will be increased approximately
tighten the two bolts.
10 rpm.
Adjust Buffer Screw
c. Install the high-speed spring on the plunger and
install the spring assembly in the governor
With the idle speed properly set, adjust the buffer
h o u s i n g . Install the spring retainer in the
screw as follows:
governor housing and tighten it securely. The
maximum no-load speed varies with the full-load
1. With the engine running at normal operating
operating speed desired.
temperature, turn the buffer screw in (Fig. 9) so it
contacts the differential lever as lightly as possible and
d. Start the engine and recheck the no-load speed.
still eliminates engine roll.
Repeat the procedure as necessary to establish the
no-load speed required.
NOTE: Do not increase the engine idle speed
more than 15 rpm with the buffer screw.
Adjust Idle Speed
2. Recheck the maximum no-load speed. If it has
With the maximum no-load speed properly adjusted,
adjust the idle speed as follows:
increased more than 25 rpm, back off the buffer screw
until the increase is less than 25 rpm.
1. With the engine running at normal operating
temperature and with the buffer screw backed out to
3. Hold the buffer screw and tighten the lock nut.
Fig. 8 - Adjusting Engine Idle Speed
Fig. 9 - Adjusting Buffer Screw
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