Chevrolet DB90 Series, Service Manual

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Sec. 6C-71
53 AND 71 SERIES DIESEL ENGINES
Figure 14—Checking Com pression Pressure ITypical)
Figure 13—Locating a M isfiring C ylinder (Typical)
C om pression p r e ssu r e is affected by altitude
a s follow s:
Min. C om pression P r e ssu r e , P s i
Altitude, Feet
53 S eries 71 S e r ie s
Above Sea L evel
540 515
0
500 480
2,500
465
440
5,000
430 410
7,500
395
380
10,000
6. P erfo rm Steps 2 through 5 on each cylinder.
The com p ression p r e ssu r e in any one cylinder
should not be le s s than 515 p si on S e r ie s 71 (540
p s i for 53 S e r ie s engine) at 600 rpm at se a le v e l.
In addition, the variation in c o m p r e ssio n p r e ssu r e s
betw een cylin d ers of the engine must not exceed
25 p si at 600 rpm . Low cylinder p r e ssu r e s may
re su lt from any one of se v e r a l cau ses:
a. P iston rings may be stuck or broken. To
determ ine the condition of the rin gs, rem ove the
a ir box cover and inspect them by p re ssin g on the
com p ression rin gs with a blunt tool (fig. 15). A
broken or stuck com p ression ring w ill not have a
"spring like" action.
b. C om pression p r e ssu r e may be leaking past
the cylinder head gasket, valve se a ts, burned or
broken v a lv e s, injector tubes, or through a hole in
the piston.
FUEL QUALITY
The quality of fuel o il used for d ie se l engine
operation is a m ajor factor in sa tisfa cto ry engine
perform ance and lif e . The fuel o ils se le c te d must
be clean, com pletely d istille d , stab le, an d n on -cor-
r o siv e . E n list your su p p lie r 'sa id in obtaining prop­
er fuel o il. The resp o n sib ility for clean fuel lin e s
r e s t s with fuel su p p lier a s w ell a s with operator.
Figure 15—Inspection for Broken or Stuck Piston Rings (Typical)
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL SUPPLEMENT