Air Leakage Tests; Unloader Piston Leakage; Discharge Valve Leakage; Removal And Disassembly - BENDIX TU-FLO 750 COMPRESSOR Manual

AIR LEAKAGE TESTS

Compressor leakage tests need not be performed on a regular
basis. These tests should be performed when; it is sus-
pected that discharge valve leakage is substantially affecting
compressor build-up performance, or when it is suspected
that the compressor is "cycling" between the load and un-
loaded modes due to unloader piston leakage.
These tests must be performed with the vehicle parked on a
level surface, the engine not running, the entire air system
completely drained to 0 P.S.I., and the inlet check valve
detail parts removed, if applicable.

UNLOADER PISTON LEAKAGE

The unloader pistons can be checked for leakage as fol-
lows: with the cylinder head removed from the compressor
and the inlet flange securely covered, apply 120 psi of air
pressure to the governor port. Listen for an escape of air at
the inlet valve area. An audible escape of air should not be
detected.

DISCHARGE VALVE LEAKAGE

Unloader piston leakage must be repaired before this test is
performed. Leakage past the discharge valves can be de-
tected as follows: Remove the discharge line and apply shop
air back through the discharge port. Listen for an escape of
air at the compressor inlet cavity. A barely audible escape of
air is generally acceptable.
If the compressor does not function as described above or if
the leakage is excessive, it is recommended that it be re-
turned to the nearest authorized Bendix distributor for a
factory remanufactured compressor. If it is not possible, the
compressor can be repaired using a genuine Bendix cylin-
der head maintenance kit. Retest the cylinder head after
installation of the kit.

REMOVAL AND DISASSEMBLY

GENERAL
The following disassembly and assembly procedure is pre-
sented for reference purposes and presupposes that a major
rebuild of the compressor is being undertaken. Several main-
tenance kits are available which do not require full
disassembly. The instructions provided with these parts and
kits should be followed in lieu of the instructions presented
here.
REMOVAL
These instructions are general and are intended to be a
guide, in some cases additional preparations and precau-
tions are necessary.
1. Block the wheels of the vehicle and drain the air pres-
sure from all the reservoirs in the system.
8
2. Drain the engine cooling system and the cylinder head
of the compressor. Identify and disconnect all air, water
and oil lines leading to the compressor.
3. Remove the governor and any supporting bracketry at-
tached to the compressor and note their positions on
the compressor to aid in reassembly.
4. Remove the discharge and inlet fittings, if applicable,
and note their position on the compressor to aid in
reassembly.
5. Remove the flange or base mounting bolts and remove
the compressor from the vehicle.
6. Remove the drive gear(s) or pulley from the compressor
crankshaft using a gear puller. Inspect the pulley or gear
and associated parts for visible wear or damage. Since
these parts are precision fitted, they must be replaced if
they are worn or damaged.
PREPARATION FOR DISASSEMBLY
Remove road dirt and grease from the exterior of the com-
pressor with a cleaning solvent. Before the compressor is
disassembled, the following items should be marked to show
their relationship when the compressor is assembled. Mark
the rear end cover in relation to the crankcase. Mark the
base plate or base adapter in relation to the crankcase.
A convenient method to indicate the above relationships is
to use a metal scribe to mark the parts with numbers or
lines. Do not use marking methods such as chalk that can
be wiped off or obliterated during rebuilding.
CYLINDER HEAD
Remove the six cylinder head cap screws (1) and tap the
head with a soft mallet to break the gasket seal. Remove
the unloader cover plate cap screws (2), lockwashers (3)
and the unloader cover plate (4). Scrape off any gasket
material (5) from the cover plate, cylinder head and crank-
case.
1. Remove the unloader pistons (7), o-rings (6) and springs
(8).
2. Inspect the unloader piston bushings (9) for nicks, wear,
corrosion and scoring. It is recommended that the com-
pressor be replaced if it is determined that the unloader
bushing is damaged or worn excessively.
Before disassembling the discharge valve mechanism, mea-
sure and record the discharge valve travel (from closed to
completely open).
3. If the measured discharge valve travel exceeds .046
inches, the compressor should be replaced. If the
discharge valve travel does not exceed .046, using a
9/16" Allen wrench, remove the discharge valve seats
(18), valves (17) and valve springs (16).