S ec. 6C-75
AIR B O X PRESSURE TEST
(Refer to Figure 19)
P roper a ir box p r e ssu r e is required to main
tain su fficien t a ir for com bustion and scavenging
of the burned g a se s.
To check the a ir box p r e ssu r e connect a man
om eter to the air box drain tube. (fig. 19).
Check the readings obtained at various speeds
with the sp ecifica tio n s in the chart.
AIR BOX PRESSURE (Min. in Inches of Mercury)
Max. Exhaust Back P r e s s u r e (Full Load)
Engine
6V-53
6-71
V-71
SPEED (RPM)
1200
3.2
2.3
1800
7.6
6.4
2100
10.1
8.2
2600
8.4
(Zero Exhaust Back P ressu re)
6V-53
5.2
6-71
1.7
4.3
6.0
V-71
1.1
3.8
5.0
Lack of pow er or black or grey exhaust sm oke
a re a lso indications of low a ir box p r e ssu r e .
If l e s s than m inimum air box p r e ssu r e is in
dicated, som e restric tio n is causing high air intake
vacuum , and it may be caused by:
1. E m ergency shut-off door adjusted wrong.
2. R estricted or damaged a ir clea n er s.
3. Worn or damaged blow er due to im proper
adjustm ent.
4. Leaking end plate g a sk ets.
5. Clogged blow er a ir inlet scre en .
If e x c e s s iv e a ir box p r e ssu r e is indicated,
th ere is a r estr ic tio n in cylinder lin e r p orts or
the exhaust sy ste m .
AIR INTAKE RESTRICTION
(R efer to Figure 20)
E x c e ssiv e r e stric tio n of the air inlet w ill af
fe ct the flow of a ir to the cylin d ers and re su lt in
poor com bustion and la ck of pow er. Consequently,
the restrictio n must be kept a s low a s p o ssib le
considering the s iz e and capacity of the air clea n er.
An obstruction in the a ir inlet sy ste m or dirty or
dam aged a ir clean ers w ill resu lt in a high blower
in let restrictio n . The a ir inlet restrictio n may be
checked with a w ater m anom eter connected to a
fitting in the air intake housing.
On som e m odels a d rilled hole i s provided for
th is connection (fig. 20). On m odels where a d rilled
hole is not provided, it i s n e c e ssa r y to rem ove the
blow er a ir intake assem b ly and d rill and tap a hole
53 AND 71 SERIES DIESEL ENGINES
fig u re 19—A ir B ox Pressure Check (Typical)
(11/32" d rill and 1/8" pipe thread tap). The hole
sgould be located at point above em ergency stop. 1
The air intake re str ic tio n should be checked
at a sp ecific engine speed. Then, the a ir clean er
and ducting should be rem oved from the air in let
housing and the engine again operated at the sam e
speed w hile noting the m anom eter reading.
The difference between the two readings, with
the air clean er and ducting and without the air
clean er and ducting, is the actual restrictio n caused
by the a ir clean er and ducting.
Check the norm al air intake vacuum at various
sp eed s (at no-load) and com pare the r e su lts with
the follow ing chart:
AIR INTAKE RESTRICTIONS
(In Inches of Water)
Max. With D irty A ir C leaner (O il Bath o r Dry)
SPEED (RPM)
Engine
6V-53
6-71
V -71
1200
12.4
12.4
1800
25.0
25.0
2100
25.0
25.0
2600
24.5
Max. With Clean A ir Cleaner
(Oil Bath or Dry) With P reclea n er
6V-53
6-71
8.7
13.4
15.9
14.7
V -71
8.7
13.4
15.9
Max. With Clean A ir C leaner (Dry) No P re c le a n e r
6V-53
6-71
5.2
9.1
11.5
9.2
V -71
5.2
9.1
11.5
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL SUPPLEMENT
Summary of Contents for DB90 Series
Page 1: ...HEAVY DUTY TRUCK SUPPLEMENT...
Page 8: ...Sec 0 2 LUBRICATION Figure 1 Lubrication Chart Conventional Cab M odels...
Page 10: ...Sec 0 4 LUBRICATION CHEVROLET SERIES 70 90 HEAVY DUTY TRUCK SHOP MANUAL SUPPLEMENT...
Page 12: ...Sec 0 6 LUBRICATION CHEVROLET SERIES 70 90 HEAVY DUTY TRUCK SHOP MANUAL SUPPLEMENT...
Page 14: ...Sec 0 8 LUBRICATION CHEVROLET SERIES 70 90 HEAVY DUTY TRUCK SHOP MANUAL SUPPLEMENT...
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