BENDIX TU-FLO 750 COMPRESSOR Service Data - Page 8

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AIR LEAKAGE TESTS

Compressor leakage tests need not be performed on a

regular basis. These tests should be performed when; it

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 gas-

ket material (5) from the cover plate, cylinder head and

crankcase.

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 compressor be replaced if it is determined that the

unloader bushing is damaged or worn excessively.

Before disassembling the discharge valve mechanism,

measure 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).