Chevrolet 70 1969 Series, Shop Manual

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AIR COMPRESSORS AND GOVERNORS 6T-3
Gear driven compressor models are flange-
mounted to an adapter assembly on rear of gear
train cover, and are driven directly from engine
camshaft. A hub with internal fiber teeth is keyed
to compressor crankshaft and secured by a nut
and cotter pin (fig. 3). An internal-toothed fiber
drive disc is bolted to the engine camshaft gear.
A drive coupling assembly is splined to fiber hub
at one end and camshaft drive disc at the other
end. Figure 3 below illustrates cross-section
view of 70 and 80 models gear drive.
COMPRESSOR LUBRICATION
Lubricating oil, under pressure from the en­
gine lubricating system, enters drilled crankshaft
through the crankshaft bearing cap and lubricates
the connecting rod bearings. Some of the oil that
flows between sides of connecting rod bearings
and cheeks on crankshaft is sprayed upward. This
oil lubricates the piston pin bushings and the
cylinder walls. The oil drains from compressor
into the mounting bracket and returns directly to
the engine crankcase. Oil lines should be kept
open freely for proper compressor lubrication.
Figure 3 — Flange Mounted Com pressor Drive
COMPRESSOR AIR INTAKE
There are four different air strainers (fil­
ters) used on these compressors. There are three
used on Midland-Ross air compressors made of
hair, paper fibers, or paper. The two used on
Bendix-Westinghouse air compressors are made
of paper or polyurethane foam. The purpose of
each is to filter incoming air and to remove im ­
purities, moisture, dirt, etc., from incoming air
before it is compressed into air brake system.
The compressor runs continuously while the
engine is running but the actual compression of air
is controlled by the governor and the unloading
mechanism. During the downstroke of the piston
(inlet valve open) a slight vacuum is created,
drawing atmospheric air through the filter into
the cylinder chamber. This air is compressed by
the upward piston stroke (inlet valve closed) and
is forced out through the discharge valve into the
truck air brake system (reservoir).
Of the five different filter elements used,
three can be cleaned and reinstalled in the com­
pressor but the paper type C A N N O T be cleaned
and reused. Refer to L U B R IC A T IO N (SEC. 0) for
method of cleaning and interval of service. Refer
to figure 4 for illustration of four of the elements.
AIR COMPRESSOR AND
GOVERNOR MAINTENANCE
Service compressor air strainer at intervals
recommended in L U B R IC A T IO N (SEC. 0). Per­
form the following inspection and maintenance
operations at intervals determined by truck oper­
ating conditions.
1. Remove cylinder head and clean carbon
from inlet and discharge valves. If valves are
damaged in any way, replace with new parts.
2. Make sure compressor discharge line is
not choked with carbon.
3. Check governor cut-in and cut-out pres­
sures and adjust, if necessary. Refer to “ Gover­
nor Adjustment” in this section.
4. Check compressor and bracket mounting
bolts for looseness, and tighten if necessary.
5. Make sure all oil, water, and air line con­
nections are tight and not leaking.
6. Check compressor drive belt tension and
adjust if necessary.
7. When draining engine cooling system to
prevent freezing, be sure to remove drain plug
from compressor cylinder block on water-cooled
models.
8. Check compressor mounting bolts, es­
pecially of a gear driven compressor as a loose
mounting will result in severe damage to drive
coupling components.
CHEVROLET SERIES 70-80 HEAVY DUTY TRUCK S H O P M A N U A L