Check the readings obtained at various
bricating oil through the breather tube,
speeds (at no load) with the Engine Op-
crankcase ventilator or dipstick hole in
erating Conditions in Subsection 11A.
the cylinder block is indicative of exces-
sive crankcase pressure.
Air Box Pressure
The causes of high crankcase pressure
may be traced to excessive blow-by due
Proper air box pressure is required to
to worn piston rings, a hole or crack in
maintain sufficient air for combustion and
a piston crown, loose piston pin retain-
scavenging of the burned gases.
Low
ers, worn turbocharger oil seals, defec-
air box pressure is caused by a high air
tive blower, cylinder head or end plate
inlet restriction, damaged blower rotors,
gaskets,
or excessive back pressure.
an air leak from the air box (such as
Also, t h e b r e a t h e r t u b e o r c r a n k c a s e
leaking end plate), or a clogged blower
ventilator should be checked for ob-
air inlet screen.
Lack of power or black
structions.
or grey exhaust smoke are indications of
low air box pressure.
Check the crankcase pressure with a ma-
nometer connected to the oil level dip-
High air box pressure can be caused by
stick opening in the cylinder block.
partially plugged cylinder liner ports.
Check the readings obtained at various
engine s p e e d s w i t h t h e E n g i n e O p e r -
Check the air box pressure with a ma-
ations Conditions in Subsection 11A.
nometer connected to an air box drain
tube.
NOTE
Check the readings obtained at various
The dipstick adaptor must not be
speeds with the Engine Operating Condi-
below the level of the oil when
tions in Subsection 11A.
checking the crankcase pressure.
Air Inlet Restrictions
Exhaust Back Pressure
Excessive restriction of the air inlet will
affect the flow of air to the cylinders and
A slight pressure in the exhaust system
result in poor combustion and lack of
is normal. However, excessive exhaust
power. Consequently the restriction
back pressure seriously affects engine
m u s t be kept as low as possible consider-
operation. It may cause an increase in
ing the size and capacity of the air
the air box pressure with a resultant
cleaner. An obstruction in the air inlet
loss of efficiency of the blower. This
system or dirty or damaged air cleaner
means less air for scavenging which re-
will result in a high blower inlet re-
sults in poor combustion and higher
striction.
temperatures.
Check the air inlet restriction with a wa-
Causes of high exhaust back pressure
ter manometer connected to a fitting in
are usually a result of an inadequate or
the compressor inlet. The restriction at
improper type of muffler, an exhaust
this point should be checked at a specific
pipe which is too long or too small in di-
engine speed. Then the air cleaner and
ameter, an excessive number of sharp
ducting should be removed from the air
bends in the exhaust system, or ob-
inlet housing and the engine again oper-
structions such as excessive carbon
ated at the same speed while noting the
formations or foreign matter in the ex-
manometer reading.
haust system.
The
difference
between
the
two
Check the exhaust back pressure, meas-
readings, with and without the air clean-
ured in inches of mercury, with a ma-
er and ducting, is the actual restriction
nometer. Check the exhaust back
caused by the air cleaner and ducting.
pressure in the exhaust piping 6" to 12"
from the turbine outlet. The tapped hole
Check the normal air inlet vacuum at var-
must be in a comparatively straight pipe
ious speeds (at no load) and compare the
area for an accurate measurement.
results with the Engine Operating Condi-
tions in Subsection 11A.
Engines
4A-5
