Engine Tune-Up
DETROIT DIESEL
Fig. 6 - Adjusting Idle Speed
Fig. 7 - Adjusting Buffer Screw
installation or removal of shims, recheck the governor
gap. If readjustment of the governor gap is required, the
Adjust Buffer Skew
position of the injector racks must be rechecked.
1. With the engine running at normal operating
NOTE: Governor stops are used to limit
temperature, turn the buffer screw in (Fig. 7) so that it
the compression of the governor spring
contacts the differential lever as lightly as possible and
which determines the maximum speed of
still eliminates engine roll.
the engine.
NOTE: Do not increase the engine idle
Adjust Idle Speed
speed more than 15 rpm with the buffer
screw.
With the maximum no-load speed properly adjusted,
adjust the idle speed as follows:
2. Hold the buffer screw and tighten the lock nut.
1. Place the stop lever in the RUN position and the
Adjust Booster Spring
speed control lever in the IDLE position.
With the engine idle speed adjusted, adjust the booster
2. With the engine running at normal operating
spring as follows:
temperature, back out the buffer screw to avoid contact
with the differential lever.
1. Move the speed control lever to the idle speed
position.
3. Loosen the lock nut and turn the idle speed
adjusting screw (Fig. 6) until the engine is operating at
2. Refer to Fig. 8 and loosen the booster spring
approximately 15 rpm below the recommended idle
retaining nut on the speed control lever. Loosen the
speed.
lock nuts on the eye bolt at the opposite end of the
booster spring.
The recommended idle speed is 550 rpm, but may vary
with special engine applications.
3. Move the spring retaining bolt in the slot of the
speed control lever until the center of the bolt is on or
4. Hold the idle speed adjusting screw and tighten the
slightly over center (toward the idle speed position) of an
lock nut.
imaginary line through the bolt, lever shaft and eye bolt.
Hold the bolt and tighten the lock nut.
4. Start the engine and move the speed control lever
to the maximum speed position and release it. The
lever should return to the idle speed position. If it does
not, reduce the tension on the booster spring. If it does,
continue to increase the spring tension until the point is
reached where it will not return to idle.
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