Removal And Disassembly; Air Leakage Tests; Unloader Piston Leakage; Discharge Valve Leakage - BENDIX TU-FLO 550 COMPRESSOR Manual

speed), and record the time taken to raise the system
pressure a selected range (for example, from 90 to 120
psi, or from 100 to 120 psi, etc.) and record it in the
vehicle's maintenance fi les. Subsequent build-up times
throughout the vehicle's service life can then be compared
to the fi rst one recorded. (Note: the 40 second guide in
the test above does not apply to this build-up time.) If the
performance degrades signifi cantly over time, you may
use the Advanced Troubleshooting Guide for Air Brake
Compressors, starting on page A-1 of this document, to
assist investigation of the cause(s).
Note: When comparing build-up times, be sure to make
an allowance for any air system modifi cations which would
cause longer times, such as adding air components or
reservoirs. Always check for air system leakage.

AIR LEAKAGE TESTS

Compressor leakage tests need not be performed on a
regular basis. These tests should be performed when; it
41
is suspected 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 unloaded 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 follows:
with the cylinder head removed from the compressor and
the inlet fl ange 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
detected 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
returned 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
cylinder head maintenance kit. Retest the cylinder head
after installation of the kit.

REMOVAL AND DISASSEMBLY

GENERAL
The following disassembly and assembly procedure is
presented for reference purposes and presupposes that
a major rebuild of the compressor is being undertaken.
Several maintenance 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
precautions are necessary.
1. Block the wheels of the vehicle and drain the air
pressure from all the reservoirs in the system.
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
attached to the compressor and note their positions
on the compressor to aid in reassembly.
4. Remove the discharge and inlet fi ttings, if applicable,
and note their position on the compressor to aid in
reassembly.
5. Remove the fl ange 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 fi tted, they must be replaced
if they are worn or damaged.
PREPARATION FOR DISASSEMBLY
Remove road dirt and grease from the exterior of the
compressor 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