GMC 4000 Series Service Manual page 393

Sec. 6T
Page 382
AIR COMPRESSORS A N D GOVERNORS
Figure 2 — Disposable Air Filter (Typical)
The slotted end of the arm is attached with a nut
and bolt to an adjusting arm bracket which is fas­
tened to the air com pressor.
The air com pressor is mounted on a base with
four bolts or four bolts and nuts. This base incor­
porates a lubricating oil return drain hole and a
boss which perm its the use of one large pivot bolt
or two sm aller pivot bolts as a method of fastening
the bottom of the air com pressor. This base also
provides a pivot point for drive belt tension adjust­
ment. The pivot bolt and nut secure the air com­
p ressor assembly to a support bracket which is
attached to the vehicle engine at the cylinder block
or lower front engine cover (dependent on vehicle
model).
The size, shape, and relative arrangement of
the adjusting arm, the adjusting arm bracket, the
base and the support bracket are determined by
the requirements for each individual model.
All com pressors used by these models are
belt-driven and are equipped with a proper size
pulley, to produce the rpm recommended by the
manufacturer. When replacing a pulley, it is of the
utmost importance that the correct one be used.
Some pulleys have a puller groove in the hub.
Use this groove when removing pulley to prevent
damage. Use extra care in removing a pulley with­
out the groove.
For belt tension adjustment, refer to procedure
under ''Drive Belt Maintenance and Adjustment"
later.
COMPRESSOR LUBRICATION
Lubricating oil, under pressure from the en­
gine lubrication system , enters drilled crankshaft
G M C S E R V I C E M A N U A L
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
w alls. The oil drains from com pressor into the
mounting bracket and returns directly to the engine
crankcase.
these com pressors are of the replaceable paper-
type. Bendix-Westinghouse air com pressors have
an air cleaner which snaps on and off for replace­
ment; while Midland-Ross air com pressors have
screw-on and -off type air cleaner. The purpose of
T-3482
filters is to filter incoming air and to remove im ­
purities, moisture, dirt, etc., before it is com­
pressed into the vehicle air brake system .
reinstalled, but must be replaced with new filter.
Filter should be checked at intervals depending on
location and climate in which vehicle operates.
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, draw­
ing atmospheric air through the filter into the cyl­
inder chamber. This air is com pressed by the up­
ward piston stroke (inlet valve closed) and is forc­
ed out through the discharge valve into the truck
air brake system (reservoir).
recommended in LUBRICATION (SEC. 0). Perform
the following inspection and maintenance operations
at intervals determined by truck operating con­
ditions.
from inlet and discharge valves. If valves are
damaged in any way, replace with new parts.
not choked with carbon.
sures and adjust, if necessary. Refer to "Governor
Adjustment" later in this section.
bolts for looseness, and tighten if necessary.
are tight and not leaking.
adjust if necessary.
COMPRESSOR AIR INTAKE
Air strainer (filters, fig. 2) used on any of
The f ilt e r elem en t CANNOT be clea n ed and
The compressor runs continuously while the
AIR COMPRESSOR A N D
GOVERNOR MAINTENANCE
Service com pressor air strainer at intervals
1. Remove cylinder head and clean carbon
2. Make sure com pressor discharge line is
3. Check governor cut-in and cut-out p res­
4. Check com pressor and bracket mounting
5. Make sure all oil, and air line connections
6. Check compressor drive belt tension and