Chevrolet DB90 Series, Service Manual

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S ec. 6C-67
53 AND 71 SERIES DIESEL ENGINES
ENGINE TIMING CHART
ENGINE
STANDARD TIMING ADVANCED TIMING
RETARDED
1 TOOTH STANDARD
ADVANCED
1 TOOTH
RETARDED
1 TOOTH STANDARD
ADVANCED
1 TOOTH
*6V-53
**6-71 & 8V-71
12V-71
0.174"-0.184"
0.192"-0.202"
0.192"-0.202"
0
.
201
"-
0
.
211
"
0.225"-0.235"
0.225"-0.235"
0.227"-0.237"
0.257"-0.267"
0.257"-0.267"
0
.
201
"-
0
.
211
"
0.225"-0.235"
0.227"-0.237"
0.257"-0.267" 0.253"-0.263"
0.284"-0.294"
♦Engines built before Serial Number 6D-66099 use standard timing.
**N 55 or N60 in jecto rs-stand ard tim ing; N65 injectors (brown tag identification) use Advanced Timing. T-9052
Figure 7 —Diesel Engine Tim ing Chari
CHECKING ENGINE TIMING
(53 AND 71 DIESEL ENGINES)
When an engine is su sp ected of being out of
tim e, due to an im properly a ssem b led gear train,
a check can be made without having to rem ove the
flyw heel housing to in sp ect the gear train m ark­
in g s.
NOTE: B efo re checking engine tim ing, refer
to "Engine Tim ing Chart" (fig. 7) to determ ine if
engine should have standard or advance tim ing.
A c c e ss to the vibration dam per o r crankshaft
p u lley, to mark the to p -d ead -cen ter position of the
s e le c te d piston , and to the front end of the crank­
shaft o r flyw heel fo r barring the engine over is
n e c e ssa r y in perform ing the tim ing check. Then,
p ro ceed as follow s:
1. Clean and rem ove the cylinder head rocker
co v er.
2. S elect any cylin d er for the tim ing check.
It is su ggested that a cylinder adjacent to one of
the cylinder head cover studs (whenused) be chosen
sin c e the stud may be used for mounting a dial
indicator.
3. R em ove the fuel lin e s (at the cylinder s e ­
lected) and in sta ll shipping caps on injector fuel
fittin g s to prevent the entry of dirt. Make su re that
the valve and injector rock er arm s are a ll in the
"up" p osition , then rem ove the rocker shaft bracket
b olts and sw ing the rocker arm a s s e m b lie s back
out of the way. R em ove the in jector a ssem b ly .
4. C arefully p lace (do not drop) a rod approx­
im ately M" x 12" long through the injector hole and
on top of the piston.
5. With the throttle in the "NO-FUEL" p o s i­
tion, turn the crankshaft slow ly in the d irection of
rotation of the engine, and stop when the rod rea ch ­
e s the end of its upward tr a v el. R em ove the rod
and turn the crankshaft opposite the direction of
rotation betw een 1 /1 6 and 1 /8 of a turn.
6. S elect a dial indicator with 0.001" gradu­
ation s and with a spindle m ovem ent of at le a s t 1
inch. U se su itab le mounting attachm ents for the
indicator so that it can be mounted over the in­
jecto r hole in th e cylin d er head. P rovide an exten­
sion for the spindle of the indicator. The extension
m ust be long enough to contact the p iston a s it
approaches its upper position .
7. Mount the indicator over the injector hole
and tighten mountings su fficien tly to hold the indi­
cator rigid.
NOTE: The mounting le g may be threaded into
the rocker cover stud; or, the stud may be rem oved
fro m the cylinder head and the le g threaded into
the tapped hole, depending upon the length of the rod
u sed in making up the mounting attachm ents.
Make su re that the spindle extension is fr e e
in the injector hole, does not bind, and is free to
tra v el its full 1-in ch m ovem ent.
8. P rovide a suitable pointer and attach it to
the crankshaft front cover or engine front end plate
a s illu stra ted in figu re 3. The pointer should e x ­
tend over the vibration dam per, or crankshaft
pu lley, w hichever is u sed.
9. Rotate the crankshaft in the direction of
rotation slow ly until the hand on the dial indicator
just stop s m oving.
10. Continue to rotate the crankshaft in the
d irection of rotation until the indicator hand just
sta r ts to m ove. R eset dial to "0." Continue turning
the crankshaft slow ly until the indicator reading is
0.010" — then stop turning.
11. Scribe a lin e on the damper (or crankshaft
pulley) (fig. 8) in lin e with the end of the p oin ter.
12. Rotate the crankshaft opposite the d ir e c ­
tion of rotation slow ly until the hand on the dial
indicator just stop s m oving.
13. Continue to rotate the crankshaft opposite
the direction of rotation until the indicator hand
just sta r ts to m ove. R eset dial to "0." Continue
turning the crankshaft slow ly until indicator read ­
ing is 0.010" — then stop turning.
14. Scribe a second lin e on the vibration damp­
er (or crankshaft pulley) in the sa m e manner a s in
Step 11 (fig. 8).
15. Scribe a third lin e halfway betw een the
fir s t two lin e s . T his i s p o sitiv e to p -d ea d -cen ter.
The th ree scrib ed lin e s a re shown on the crank­
shaft pulley in figure 3. R em ove the indicator from
the engine.
NOTE: Make certain that the crankshaft pulley
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