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