Chevrolet 70 Series 1970, Service Manual

Page: 449 / 841

53 AND 71 SERIES DIESEL ENGINES 6C-52
Figure 5—Checking Fuel Pressure at Injector
ENGINE OIL PRESSURE TEST
To check operating o il p r e ssu r e connect the
0 - 1 0 0
p r e ssu r e gauge to the o il g a llery or into o il
lin e from g a llery to o il filte r .
Start engine. For sa tisfa cto ry p r e ssu r e s re fer
to follow ing chart:
OIL PRESSURE
Engine
SPEED (RPM)
1 2 0 0
1800
2 1 0 0 2 2 0 0
2600
6V-53
6-71
8V-71
30-60
Min. 18
35-55
Min. 25
38-60
Min. 27
50-70
Min. 28
40-60
Min. 30
50-70
M-n. 30
40 -6 0
Min. 30
4 0 -6 0
Min. 32
COOLING SYSTEM
R efer to ENGINE COOLING SYSTEM (SEC.
6
K) of this manual for cooling sy ste m ch eck s.
CRANKCASE PRESSURE
The cran k case p r e ssu r e indicates the amount
of a ir that has p a sse d betw een the o il control rings
and the lin er into the cran k case, m ost of which is
clean a ir from the a ir box. A sligh t p r e s s u r e in the
cran k case is needed to prevent the entrance of dust.
A lo s s of eiigine lubricating o il through the
breather tube, cran k case ventilator, or dipstick
hole in the cylinder block is indicative of e x c e s s ­
iv e cran k case p r e ssu r e . The maximum crankcase
p r e ssu r e is shown in the follow ing chart:
CRANKCASE PRESSURE
(Max. in Inches of Water)
SPEED (RPM1
Engine
1 2 0 0
1800
2 1 0 0
2600
6V -53
1 .0
6-71
2 . 0 2 .8
3.1
8V -71 0.5
1 .1
1.5
The c a u ses of high cran k case p r e ssu r e may be
tra ced to e x c e s s iv e blow-by due to worn piston
r in g s, a hole or crack in a p iston crown, lo o se
p iston pin re ta in e r s, worn blow er o il s e a ls , d efec­
tiv e blow er, cylinder head or end plate gask ets,
or e x c e s s iv e exhaust back p r e ssu r e . A lso , the
b reath er tube o r crankcase ventilator should be
checked for ob stru ction s.
The crankcase p r e ssu r e may be checked with
the m anom eter in the Engine D iagn osis T est Kit
(J-9531-01) (fig.
6
). The m anom eter sh o u ld b eco n ­
nected to the o il le v e l dipstick opening in the c y l­
inder block. Check the readings obtained at various
engine sp eed s with the sp ecifica tio n s in the chart.
EXHAUST BACK PRESSURE
A sligh t p r e ssu r e in the exhaust sy ste m is
norm al. H ow ever, e x c e s s iv e exhaust b a ck p ressu re
se r io u sly a ffects engine operation. It may cau se an
in c r e a se in the a ir box p r e ssu r e with a resultant
lo s s of efficien cy of the blow er. This m eans l e s s
a ir for scavenging which r e su lts in poor com bus­
tion and higher tem p eratu res. The maximum ex ­
haust back p r e ssu r e (no-load) is shown in the fo l­
low ing chart:
EXHAUST BACK PRESSURE - NO LOAD
(Max. in Inches of Mercury)
SP EED (RPM)
Engine
1 2 0 0
1800
2 0 0 0 2 1 0 0
2600
6V -53
6-71
8V-71
1 .2
.09
2 .8
2 .1
3.5
2 . 6
3.5
2 . 6
2.7
Due to variation s in exhaust sy s te m s (hori­
zontal or v e r tic a l stacks) the above chart is typical.
C auses of high exhaust back p r e ssu r e are
u su ally a resu lt of an inadequate o r im proper type
of m uffler, an exhaust pipe which is too long or too
sm a ll in diam eter, an e x c e s s iv e number of sharp
bends in the exhaust sy ste m , or obstructions such
a s e x c e s s iv e carbon form ation o r foreign m atter
in the exhaust sy ste m .
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL