Chevrolet DB90 Series, Service Manual

Page: 71 / 242

S ec. 6C -65
Lock adjusting sc r e w with lock nut when id le speed
i s approxim ately 15 rpm below d esired settin g.
BUFFER SCREW ADJUSTMENT
With the id le sp eed s e t, the buffer sc r e w may
be adjusted a s follow s:
1. With the engine running at norm al operating
tem perature, turn the buffer sc r e w in so that it
con tacts the d ifferen tial le v e r a s ligh tly a s p o s­
sib le and s t ill elim in a tes the engine r o ll.
NOTE: Do not in c r e a se the engine idle speed
m ore than 15 rpm with the buffer sc r e w .
2. Buffer sc r e w can be checked for proper
adjustm ent by a ccelera tin g engine and d e -a c c e le r -
ating. When engine com es to id le from d e -a c c e l-
eration it should r o ll one to two tim e s and le v e l
off to sm ooth id le.
NOTE: If engine r o lls or su rg es m ore than
th ree tim e s, the buffer sc r e w needs to be adjusted
in slig h tly .
If engine does not r o ll one to two tim e s, the
buffer sc r e w i s adjusted in too fa r.
3. With buffer sc r e w properly adjusted, hold
the buffer sc r e w and tighten the lock nut and r e ­
check.
4. R echeck the maximum n o-load speed. If it
has in c r e a se d m ore than 25 rpm , back off the buffer
sc r e w until the in c r e a se i s l e s s than 25 rpm.
5. A fter the governor tune-up has been com ­
p leted , in sta ll the variable low sp eed adjuster
coupling and spring housing. Center the adjusting
coupling b efo re secu rin g the housing a ssem b ly to
the governor housing with two lock w a sh ers and
b o lts. In stall the flex ib le shaft and manual control
a ssem b ly .
TORQUE REQUIREMENT FOR INJECTOR
RACK CONTROL LEVER SCREWS
(53 AND 71 DIESEL ENGINES)
O vertightening of the injector rack control
le v e r sc r e w s can cau se dam age to the injector
control tube.
The recom m ended torque fo r th ese sc r e w s is
24 to 36 in .-lb s . which can be obtained generally
usin g a scre w d riv er with a on e-in ch diam eter
handle and turning it with one hand. U sing a torque
ENGINE REPLACEMENT-HH
V8 DIESEL ENGINE REM OVAL
The procedure on page 6C-27 of S ervice
Manual ST 135-70 w ill apply with the addition of
the follow ing information:
53 AND 71 SERIES DIESEL ENGINES
Figure
4 —lo w
Speed Spring G a p A dju stm en t (Typical)
w rench with a screw d riv e r adapter, fo r final ad­
justm ent, elim in a tes the touch or fe e l by hand that
is helpful in making uniform rack settin g s, im ­
portant to good engine p erform ance.
Overtightening of th ese sc r e w s can re su lt if
a la rg er screw d riv e r is u sed and both hands are
applied to tighten the s c r e w s . T e s ts show that the
sc r e w s start to cut into the control tube when
torque ex ceed s 40 inch-pounds.
TORQUE WRENCH SPECIFICATIONS
C ylinder head b olts and nuts torque on p a g es
6C -15, 6C-25 and 6C-48 in S T 135-70 S ervice
Manual should be 175 to 185 foot-pounds instead
of 190 to 200 foot-pounds.
INJECTOR VALVE OPENING
PRESSURE
Injector valve opening p r e ssu r e on p ages 6C -8
and 6C-25 in S e rv ic e Manual ST 135-70 should
read 2300 and 3300 p s i in stead of 2000 to 3200 p si.
AND JH MODELS
It i s not n e c e ssa r y to r a is e the cab if a dolly,
to support and m ove engine forw ard b efo re lifting
the engine, i s a v a ila b le. A lso , in so m e in sta n ces
it may not be n e c e ssa r y to rem ove the front c r o s s
m em b ers.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL SUPPLEMENT