BENDIX TU-FLO 750 COMPRESSOR Mounting instructions

1
®
SD-01-344
DESCRIPTION
The function of the air compressor is to provide and main-
tain air under pressure to operate devices in the air brake
and/or auxiliary air systems. The Tu-Flo®750 compressor
is a two cylinder single stage, reciprocating compressor
with a rated displacement of 16.5 cubic feet per minute
at 1,250 RPM.
The compressor assembly consists of two major
subassemblies, the cylinder head and the crankcase. The
cylinder head is an iron casting which houses the inlet,
discharge, and unloader valving. (See Figure 1.) The
cylinder head contains the air inlet port and is designed
with both top and side air discharge ports. Three water
coolant ports provide a choice of coolant line connections.
Governormountingsurfacesareprovidedat both the front
and the rear of the cylinder head. The head is mounted
on the crankcase and is secured by six cap screws. The
Tu-Flo®750compressor is designedsuch that thecylinder
headcan beinstalled in oneof twopositions whichare 180
degrees apart. The crankcase houses the cylinder bores,
pistons, crankshaft and main bearings, and provides the
flange or base mounting surface.
Bendix®Tu-Flo®750 Air Compressor
BENDIX®TU-FLO®750 AIR COMPRESSOR
(CROSS SECTION)
BENDIX®TU-FLO®750 AIR COMPRESSOR
(EXTERIOR)
AIR DISCHARGE WATER OUTLET
PIECE NO.
TAG
GOVERNOR
MOUNTING
PAD
CRANKCASE
PISTON RINGS
PISTON
CRANKSHAFT
CONNECTING
ROD
INLET VALVE
SEAT
UNLOADER
INLET VALVE
CYLINDER
HEAD
END VIEW OF CYLINDER HEAD
DISCHARGE
VALVE SPRING
DISCHARGE
VALVE
DISCHARGE
VALVE STOP
AIR INLET
CRANKCASE
INLET
INLET VALVE
SPRING
DISCHARGE
VALVE SEAT
UNLOADER
COVER
WATER
INLET
CYLINDER
HEAD

2
OPERATION
The compressor is driven by the vehicle engine and is
operating continuously while the engine is running.Actual
compressionof airis controlled bythe compressorunload-
ing mechanism and the governor. The governor, which is
generallymounted onthe compressor,maintainsthebrake
system air pressure to a preset maximum and minimum
pressure level.
INTAKE AND COMPRESSION OF AIR (LOADED)
During the down stroke of the piston, a slight vacuum is
createdbetweenthe top ofthepiston andthecylinder head,
causingthe inletvalve tomove offitsseat andopen. (Note:
The discharge valve remains on its seat.)Atmospheric air
is drawn through the air strainer and the open inlet valve
into the cylinder (see Figure 4). As the piston begins its
upward stroke, the air that was drawn into the cylinder on
the down stroke is being compressed.Air pressure on the
inlet valve plus the force of the inlet spring, returns the
inlet valve to its seat and closes. The piston continues the
upward stroke and compressed air pushes the discharge
valve off its seat and air flows by the open discharge
valve, into the discharge line and to the reservoirs (see
Figure 5). As the piston reaches the top of its stroke and
starts down, the discharge valve spring and air pressure
in the discharge line returns the discharge valve to its
seat. This prevents the compressed air in the discharge
AIR INLET
WATER
UNLOADER COVER
PLATE
AIR DISCHARGE
WATER
AIR
DISCHARGE
GOVERNOR
MOUNTING
PAD
WATER
MANUFACTURED BY BENDIX
TU-FLO 750 COMPRESSOR
BENDIX NO.
SERIAL NO.
FIGURE 2 - MOUNTING CONFIGURATIONS
Various mounting and drive configurations, as shown in
Figure 2, are supplied as required by the vehicle engine
designs. A nameplate identifying the compressor piece
number and serial number is attached to the side of the
crankcase. (Reference Figure 3.)
FIGURE 3 - NAMEPLATE
FIGURE 1 - CYLINDER HEAD
CAT MACK
(MACK STYLE)
DETROIT
DIESEL
MACK
"FOXHEAD" CUMMINS
MACK
EXTENDED

3
governor closes and exhausts the air from above
the unloader pistons. The unloader springs force the
pistons upward and the inlet valves return to their seats.
Compression is then resumed.
COMPRESSOR & THE AIR BRAKE SYSTEM
GENERAL
The compressor is part of the total air brake system, more
specifically, the charging portion of the air brake system.
As a component in the overall system its condition, duty
cycle, proper installation and operation will directly affect
other components in the system.
Powered by the vehicle engine, the air compressor
builds the air pressure for the air brake system. The air
compressor is typically cooled by the engine coolant
system,lubricated by the engine oilsupply and has its inlet
connected to the engine induction system.
As the atmospheric air is compressed, all the water vapor
originally in the air is carried along into the air system, as
well as a small amount of the lubricating oil as vapor. If an
air dryer is not used to remove these contaminants prior
to entering the air system, the majority, but not all, will
condense in the reservoirs. The quantity of contaminants
that reach the air system depends on several factors
including installation, maintenance and contaminant
handling devices in the system. These contaminants must
eitherbe eliminated priorto entering the air systemor after
they enter.
GOVERNOR
PORT
AIR
INLET
PORT
INLET
VALVE
OPEN
PISTON
MOVING
DOWN
DISCHARGE
VALVE
CLOSED
GOVERNOR
PORT
INLET
VALVE
CLOSED
PISTON
MOVING
UP
FIGURE 4 - OPERATIONAL-LOADED (INTAKE)
FIGURE 5 - OPERATIONAL-LOADED (COMPRESSION)
GOVERNOR
PORT
DISCHARGE
PORT
AIR
INLET
PORT
FIGURE 6 - OPERATIONAL-UNLOADED
DISCHARGE
VALVE
CLOSED
UNLOADER
PISTON
DISCHARGE
VALVE
OPEN
AIR
INLET
PORT
line from returning to the cylinder bore as the intake and
compression cycle is reseated.
NON-COMPRESSION OF AIR (UNLOADED)
When air pressure in the reservoir reaches the cut-out
settingof thegovernor, thegovernor allowsair topass from
thereservoir,through thegovernorandintothecavity above
the unloader pistons. The unloader pistons move down
holding the inlet valves off their seats (see Figure 6.) With
theinlet valves heldofftheir seats bythe unloader pistons,
airispumpedback andforthbetweenthe twocylinders,and
thedischargevalvesremainclosed.Whenairpressurefrom
thereservoir drops tothe cut-in setting of thegovernor,the
INLET VALVE
HELD OPEN
BY UNLOADER
PISTON
AIR
DISCHARGE
PORT
AIR
DISCHARGE
PORT

4
DUTY CYCLE
The duty cycle is the ratio of time the compressor spends
building air to the total engine running time. Air compres-
sors are designed to build air (run "loaded") up to 25% of
the time. Higher duty cycles cause conditions that affect
airbrake charging systemperformance which mayrequire
additional maintenance. Factors that add to the duty cycle
are: air suspension, additional air accessories, use of an
undersizedcompressor, frequentstops, excessiveleakage
from fittings, connections, lines, chambers or valves, etc.
Refer to TableAin theTroubleshooting section for a guide
to various duty cycles and the consideration that must be
given to maintenance of other components.
COMPRESSOR INSTALLATION
While the original compressor installation is usually com-
pletedby thevehicle manufacturer, conditions ofoperation
andmaintenancemay require additionalconsideration.The
following presents base guidelines.
DISCHARGE LINE
Thedischarge lineallows the air, water-vaporand oil-vapor
mixture to cool between the compressor and air dryer or
reservoir. The typical size of a vehicle's discharge line,
(see column 2 of Table A in the Troubleshooting section)
assumesa compressorwith a normal(less than25%) duty
cycle,operating ina temperate climate.See Bendixand/or
other air dryer manufacturer guidelines as needed.
FIGURE 6A - SYSTEM DRAWING
Air Dryer
Reservoir Drain
Service Reservoir
(Supply Reservoir)
Compressor
Governor
(Governor plus Synchro valve
for the Bendix®DuraFlo™596
Compressor)
Discharge
Line Optional “Ping” Tank
Optional Bendix®PuraGuard®QC™
Oil Coalescing Filter
The Air Brake Charging System supplies the
compressedair forthe brakingsystem as wellas otherair
accessories for the vehicle. The system usually consists
of an air compressor, governor, discharge line, air dryer,
and service reservoir.
The discharge line must maintain a constant slope down
fromthe compressor to the airdryer inlet fittingor reservoir
to avoid low points where ice may form and block the flow.
If, instead, ice blockages occur at the air dryer or reservoir
inlet, insulation may be added here, or if the inlet fitting is
a typical 90 degree fitting, it may be changed to a straight
or 45 degree fitting. Shorter discharge line lengths or
insulation may be required in cold climates.
While not all compressors and charging systems are
equipped with a discharge line safety valve this compo-
nent is recommended. The discharge line safety valve is
installed in the cylinder head (Tu-Flo®550/750) or close to
the compressor discharge port and protects against over
pressurizing the compressor in the event of a discharge
line freezeup.
FIGURE 6B - DISCHARGE LINE SAFETY VALVE
HOLE
THREAD

5
COOLING
Air flowing through the engine compartment from the
action of the engine’s fan and the movement of the vehicle
assistsin coolingthe compressor. Coolantflowing fromthe
engine’scoolingsystemthroughconnectinglinesenters the
headand passes throughinternal passagesin the cylinder
head and is returned to the engine. Proper cooling is
importantin maintaining dischargeair temperatures below
the maximum recommended 400 degrees Fahrenheit.
Figure 8 illustrates the various approved coolant flow
connections. See the tabulated technical data in the back
of this manual for specific requirements.
AIR INDUCTION
There are three methods of providing clean air to the
Tu-Flo®750 compressor:
1. Naturally aspirated Local Air Strainer - Compressor
utilizes its own attached air strainer (polyurethane
sponge or pleated paper dry element).
2. Naturally aspirated Engine Air Cleaner - Compressor
inlet is connected to the engine air cleaner or the
vacuumside(engine aircleaner) ofthesupercharger or
turbocharger.
3. Pressurized induction - Compressor inlet is connected
to the pressure side of the supercharger or turbo-
charger.
Seethe tabulated technicaldata in theback of thismanual
for specific requirements for numbers 2 and 3 above.
DISCHARGE LINE TEMPERATURE
When the temperature of the compressed air that enters
the air dryer is within the normal range, the air dryer can
removemost of thecharging system oil.If the temperature
of the compressed air is above the normal range, oil as
oil-vapor is able to pass through the air dryer and into the
air system. Larger diameter discharge lines and/or longer
discharge line lengths can help reduce the temperature.
The air dryer contains a filter that collects oil droplets, and
a desiccant bed that removes almost all of the remaining
water vapor. The compressed air is then passed to the air
brake service (supply) reservoir. The oil droplets and the
watercollectedareautomatically purgedwhenthegovernor
reaches its "cut-out" setting.
For vehicles with accessories that are sensitive to small
amounts of oil, we recommend installation of a Bendix®
PuraGuard®QC™oilcoalescing filter,designed tominimize
the amount of oil present.
LUBRICATION
The vehicle's engine provides a continuous supply of oil
to the compressor. Oil is routed from the engine to the
compressor oil inlet. An oil passage in the compressor
crankshaft allows oil to lubricate the connecting rod crank-
shaft bearings. Connecting rod wrist pin bushings and
crankshaft ball bearings are spray lubricated.An oil return
line connected from the compressor drain outlet to the
vehicle engine crankcase allows for oil return. On flange
mounted models, the oil drains back directly to the engine
through the mounting flange.
FIGURE 7 - LUBRICATION (BASE MOUNT MODEL SHOWN)
OIL
INLET
OIL
OUTLET
WATER
IN
OR
(1 PORT
ONLY)
WATER
OUT
OR
(1 PORT
ONLY)
WATER OUT
WATER
OUT
WATER
IN
WATER
IN
FIGURE 8 - COOLING

6
If a previously unturbocharged compressor is being
turbocharged,itis recommended thattheinlet cavityscreen
(238948)be installedwith an inlet gasket (291909)on both
sides of the screen.
COMPRESSOR TURBOCHARGING PARAMETERS
Air entering the compressor inlet during the loaded cycle
must not exceed 250 degrees Fahrenheit (121 degrees
Celsius). A metal inlet line is suggested to help meet this
parameter.
The following compressor crankshaft rotative speed and
inlet pressure relationships may not be exceeded.
Crankshaft Maximum Compressor
R.P.M. Inlet Pressure
1900 RPM 30.0 psi (207 kPa)
2000 RPM 27.5 psi (190 kPa)
2100 RPM 24.0 psi (165 kPa)
2200 RPM 21.0 psi (145 kPa)
2300 RPM 19.0 psi (131 kPa)
2400 RPM 16.0 psi (110 kPa)
AIR INDUCTION
One of the single most important aspects of compressor
preventive maintenance is the induction of clean air.
The type and interval of maintenance required will vary
depending upon the air induction system used.
The intervals listed under the headings below pertain
to typical highway and street operation. More frequent
maintenance will be required for operation in dusty or dirty
environments.
0
20
25
15
35
5
30
900600
10
Compressor Speed (RPM)
Inlet Pressure (PSIG)
Turbo Limits
FIGURE 9 - TURBO LIMITS CURVE
PREVENTATIVE MAINTENANCE
Regularly scheduled maintenance is the single most
important factor in maintaining the air brake charging
system. Refer to TableAin the Troubleshooting section for
a guide to various considerations that must be given to the
maintenanceof thecompressor andother relatedcharging
system components.
Important Note: Review the warranty policy before
performing any intrusive maintenance procedures. An
extendedwarranty may be voided ifintrusive maintenance
is performed during this period.
PAPER AIR STRAINER DRY ELEMENT-PLEATED
POLYURETHANE SPONGE STRAINER
FIGURE 10 - STRAINERS
POLYURETHANE SPONGE STRAINER
Every month, 150 operating hours or 5,000 miles,
whichever occurs first, removeand wash all of theparts.
The strainer element should be cleaned or replaced. If the
element is cleaned, it should be washed in a commercial
solvent or a detergent and water solution. The element
should be saturated in clean engine oil, then squeezed
dry before replacing it in the strainer. Be sure to replace
theair strainer gasketif the entirestrainer is removedfrom
the compressor intake.

7
DRY ELEMENT - PLEATED PAPER STRAINER
Every two months, 800 operating hours or 20,000 miles
whichever occurs first, loosen the spring clip from the
unhinged side of the mounting baffle and open the cover.
Replace the pleated paper filter and secure the cleaned
cover,making surethefilterisin position.Besure to replace
the air strainer gasket if the entire air strainer is removed
from the compressor intake.
INTAKE ADAPTER
Whenthe engine air cleaneris replaced: Somecompres-
sorsarefittedwith compressor intakeadapters,which allow
the compressor intake to be connected to the engine air
induction system. In this case, the compressor receives a
supply of clean air from the engine air cleaner. When the
engineair filter is changed,the compressor intake adapter
shouldbe checked.Ifit isloose, removethe intakeadapter,
cleanthestrainer plate,if applicable,andreplace theintake
adapter gasket, and reinstall the adapter securely. Check
line connections both at the compressor intake adapter
and at the engine. Inspect the connecting line for ruptures
and replace it if necessary.
COMPRESSOR COOLING
Every 6 months, 1,800 operating hours or after each
50,000 miles whichever occurs first, inspect the com-
pressor discharge port, inlet cavity and discharge line for
evidenceof restrictions andcarboning. Ifexcessive buildup
isnoted, thoroughlyclean orreplace theaffectedparts and
closely inspect the compressor cooling system. Check all
compressor coolant lines for kinks and restrictions to flow.
Minimum coolant line size is 3/8" I.D. Check coolant lines
forinternal clogging fromrust scale.If coolant linesappear
suspicious, check the coolant flow and compare to the
tabulatedtechnical datapresent inthe backof thismanual.
Carefully inspect the air induction system for restrictions.
LUBRICATION
Every six months, 1,800 operating hours or 50,000
miles whichever occurs first, check external oil supply
and return lines, if applicable, for kinks, bends, or restric-
tions to flow. Supply lines must be a minimum of 3/16" I.D.
and return lines must be a minimum of 1/2" I.D. Oil return
linesshouldslope assharplyas possiblebackto the engine
crankcase and should have as few fittings and bends as
possible. Refer to the tabulated technical data in the back
of this manual for oil pressure minimum values.
Check the exterior of the compressor for the presence of
oilseepage andrefer totheTROUBLESHOOTING section
for appropriate tests and corrective action.
OIL PASSING
All reciprocating compressors currently manufactured will
pass a minimal amount of oil. Air dryers will remove the
majorityofoil priortoentranceinto theairbrake system.For
particularly oil sensitive systems the Bendix®PuraGuard®
QC™oil coalescing filter can be used in conjunction with
a Bendix air dryer.
If compressor oil passing is suspected, refer to the
TROUBLESHOOTING section and TABLE A for the
symptoms and corrective action to be taken. In addition,
Bendix has developed the "Bendix Air System Inspection
Cup" or BASIC test to help substantiate suspected exces-
sive oil passing. The steps to be followed when using the
BASICtest are presentedinAPPENDIXAatthe end of the
TROUBLESHOOTING section.
COMPRESSOR DRIVE
Every six months, 1,800 operating hours or 50,000
miles,whichever occurs first,checkfornoisy compressor
operation,which couldindicate aworn drive gearcoupling,
a loose pulley or excessive internal wear. Adjust and/or
replace as necessary.
If the compressor is belt driven, check for proper belt and
pulley alignment and belt tension. Check all compressor
mounting bolts and retighten evenly if necessary. Check
for leakage and proper unloader mechanism operation.
Repair or replace parts as necessary.
Every 24 months, 7,200 operating hours, or after
each 200,000 miles, perform a thorough inspection, and
dependinguponthe resultsofthis inspection orexperience,
disassemble the compressor, clean and inspect all parts
thoroughly, replace all worn or damaged parts using only
genuine Bendix replacements or replace the compressor
with a genuine Bendix remanufactured unit.
GENERAL SERVICE CHECKS
OPERATING TESTS
Vehicles manufactured after the effective date of FMVSS
121, with the minimum required reservoir volume, must
have a compressor capable of raising air system pressure
from85-100psiin 25secondsorless.Thistestisperformed
with the engine operating at maximum recommended
governedspeed.Thevehicle manufacturer mustcertify this
performanceon new vehicleswith appropriate allowances
for air systems with greater than the minimum required
reservoir volume.

8
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 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
detected as follows: Remove the discharge line and apply
shop air back through the discharge port. Listen for an
escapeofair atthecompressor inletcavity.Abarelyaudible
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
ofthe compressor. Identifyand 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 fittings, if applicable,
and note their position on the compressor to aid in
reassembly.
5. Removethe flangeor basemounting boltsand remove
the compressor from the vehicle.
6. Removethe drivegear(s)or pulley fromthecompressor
crankshaftusinga gearpuller. Inspectthepulley orgear
andassociated partsfor visible wearor 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 compressor with a cleaning solvent. Before the
compressor is disassembled, the following items should
bemarked toshow their relationshipwhen thecompressor
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,
measureandrecord thedischargevalve travel(fromclosed
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).

9
4. Remove the inlet valve stops (14), valves (17), valve
seats (11), valve springs (12) and gaskets (10). It is
recommendedthatatoolsuchasaJ-25447-B,produced
byKent MooreTool DivisionRoseville, Michiganphone
1-800-328-6657, be used to remove the inlet valve
stop.
CRANKCASE BOTTOM COVER OR ADAPTER
DISASSEMBLY
1. Removethe capscrews (22)securing thebottom cover
or adapter (21). Tap with a soft mallet to break the
gasket seal. Scrape off any gasket material (20) from
the crankcase and bottom cover or adapter.
CONNECTING ROD DISASSEMBLY
Before removing the connecting rod, mark the connecting
rods(37) andtheir caps (39)to ensurecorrect reassembly.
The connecting rod and cap are a matched set therefore
the caps must not be switched or rotated end for end.
1. Removethe connectingrod bolts (40)and bearingcaps
(39).
2. Push the pistons (26) with the connecting rods (37)
attached out the top of the cylinder bore of the crank-
case. Replace the bearing caps on the connecting
rods.
3. Remove the piston rings (23-25) from the piston. If
the piston is to be removed from the connecting rod,
remove the wrist pin teflon plugs (28) and press the
wrist pin (27) from the piston and connecting rod.
4. If the piston is removed from the rod, inspect the wrist
pin bore in the piston and bronze wrist pin bushing
(36) in the connecting rod. If excessive wear is noted
or suspected, replace the connecting rod and piston.
COMPRESSOR CRANKCASE DISASSEMBLY
1. Remove the key or keys (30) from the crankshaft (29)
andanyburrs from thecrankshaftwhere thekeyorkeys
wereremoved. (Note:Through drivecompressors may
have a crankshaft key at both ends.)
2. Remove the four cap screws (35) and lockwashers or
nuts and lockwashers that secure the rear end cover
(34) to the crankcase.
3. Removethe rearendcover (34),thrust washer (31)and
end cover oil seal ring (33), taking care not to damage
the bearing if present in the end cover.
4. Ifthe compressorhasball typemainbearings, press the
crankshaft (29) and ball bearings from the crankcase,
then press the ball bearings from the crankshaft.
5. Press the oil seal out of the compressor crankcase, if
so equipped.
CLEANING OF PARTS GENERAL
All parts should be cleaned in a good commercial grade of
solvent and dried prior to inspection.
CYLINDER HEAD
Remove carbon deposits from the discharge cavity and
rustand scalefrom thecooling cavitiesof the cylinderhead
body.Scrape allforeign matterfrom the bodysurfaces and
use shop air pressure to blow the dirt particles from the
cavities. Clean carbon and dirt from the inlet and unloader
passages.Useshop airtoblow thecarbonanddirt deposits
from the unloader passages.
OIL PASSAGES
Thoroughly clean all oil passages through the crankshaft,
crankcase,end covers, baseplate orbase adapter.Inspect
the passages with a wire to be sure. Blow the loosened
foreign matter out with air pressure.
INSPECTION OF PARTS
CYLINDER HEAD BODY
Inspect the cylinder head for cracks or damage. With the
cylinder head and head gasket secured to a flat surface
or crankcase, apply shop air pressure to one of the cool-
ant ports with all others plugged, and check for leakage
by applying a soap solution to the exterior of the body. If
leakage is detected, replace the compressor.
END COVERS
Check for cracks and external damage. If the crankshaft
main bearing (32) is installed in the end cover (34),
check for excessive wear and flat spots and replace if
necessary.
CRANKCASE
Check all crankcase surfaces for cracks and damage. On
compressors where ball bearing main bearings are used
the difference between the O.D. of the outer race and the
I.D.of thecrankcase hole shouldbe .0003in. tightto .0023
in.loose.This isto maintainthe correctfit.The compressor
must be replaced if the fit is too loose.
Oncompressorsfittedwithprecision, sleeve mainbearings,
the difference between the O.D. of the crankshaft journal
and the main bearing l.D. must not exceed .005 in. If the
clearance is greater than .005 in. the bearing must be
replaced.
The cylinder bores should be checked with inside microm-
etersor calipers. Cylinderbores which arescored or outof
round by more than .0005 in. or tapered more than .0005

10
41
31
1
2
3
4
5
6
7
8
9
23
23
24
25
24
28
27
23
35
25
24
10
11
12
13
24
37
14
36
33 32
34
29
30
38
39
40
NAMEPLATE
20
21
22
15
16
17
18
19
CRANKCASE
32
26
31
CYLINDER
HEAD
32
BALLBEARING
(MACK EXTENDED
FLANGE)
FIGURE 11 - EXPLODED VIEW
ITEM QTY DESCRIPTION ITEM QTY DESCRIPTION ITEM QTY DESCRIPTION
1 6 Cylinder Head Cap Screws 15 2 Discharge Valve Stop 29 1 Crankshaft
2 4 Unloader Plate Cap Screws 16 2 Discharge Valve Spring 30 1 Crankshaft Key
3 4 Unloader Plate Lock Washers 17 2 Discharge Valve 31 2 Thrust Washer
4 1 Unloader Plate 18 2 Discharge Valve Stop 32 2 Sleeve (or Ball) Bearing
5 1 Unloader Plate Gasket 19 1 Cylinder Head Gasket 33 1 End Cover Seal
6 2 O-ring 20 1 Base Gasket 34 1 End Cover
7 2 Unloader 21 1 Base Plate 35 4 End Cover Cap Screws
8 2 Spring 22 6 Base Plate Cap Screws 36 2 Wrist Pin Bushing
9 2 Unloader Bushing 23 6 Standard Piston Rings 37 2 Connecting Rod
10 2 Gasket 24 8 Oil Ring 38 2 Conn. Rod Inserts (Sets)
11 2 Inlet Valve Seat 25 4 Expander Ring 39 2 Connecting Rod Caps
12 2 Inlet Valve 26 2 Piston 40 4 Connecting Rod Bolts
13 2 Inlet Valve Spring 27 2 Wrist Pin
14 2 Inlet Valve Stop 28 4 Wrist Pin Button

11
in.should berebored or honedoversize. Oversizedpistons
and piston rings are available in .010 in., .020 in. and .030
in. oversizes. Cylinder bores must be smooth, straight
and round. Clearance between the cast iron pistons and
cylinder bores should be between .002 in. minimum and
.004 in. maximum.
PISTON RINGS
Check the pistons for scores, cracks or enlarged ring
grooves; replace the pistons if any of these conditions
are found. Measure each piston with a micrometer in
relation to the cylinder bore diameter to be sure the
diametrical clearance is between .002 in. minimum and
.004 in. maximum.
Check the fit of the wrist pins to the pistons and connect-
ing rod bushings. The wrist pin should be a light press fit
in the piston. If the wrist pin is a loose fit, the piston and
pin assembly should be replaced. Check the fit of the wrist
pin in the connecting rod bushing by rocking the piston.
This clearance should not exceed .0007 in. Replace the
connecting rod and cap assembly which includes the wrist
pin bushings if excessive clearance is found. Check the fit
of the rings in the piston ring grooves. Check the ring gap
withthe ringsinstalled in thecylinder bores.Refer toFigure
12 for correct gap and groove clearances.
CRANKSHAFT
Checkthe crankshaft threads,keyways, tapered ends and
allmachinedand groundsurfaces for wear, scores,ordam-
age. Standard crankshaft journals are 1.1242 in. - 1.1250
in. in diameter. If the crankshaft journals are excessively
scoredor wornor outof roundand cannotbe reground,the
compressor must be replaced. Connecting rod bear-
ing inserts are available in .010 in., .020 in. and .030 in.
undersizes for compressors with reground crankshafts.
Mainbearing journalsmust be maintained so theball bear-
ingsarea snugfitor so thatno more than.005 in.clearance
exists between the precision sleeve main bearing and the
main bearing journals on the crankshaft. Check to be sure
the oil passages are open through the crankshaft.
CONNECTING ROD BEARINGS
Usedbearinginserts mustbe replaced.The connectingrod
andcap area matchedset andtherefore thecaps mustnot
be switched or rotated end for end. Make sure the locating
tangs on the inserts engage with the locating notches in
the rod and cap. Clearance between the connecting rod
journal and the connecting rod bearing must not be less
than .0003 in. or more than .0021 in. after rebuilding.
REPAIRS
UNLOADER
Anew cylinder head maintenance kitshould beused when
rebuilding. Note: The entire contents of this kit must
be used. Failure to do so may result in compressor
failure. The unloader pistons in the kit are prelubricated
with a special lubricant piece number 239379 and need
no additional lubrication. Install the springs and unloader
pistons in their bores being careful not to cut the o-rings.
Install the unloader cover gasket and unloader cover and
secure the cover cap screws. Tighten the cap screws to
175-225 in. Ibs. in a crossing pattern after first snugging
all screws.
DISCHARGE VALVES, VALVE STOPS AND SEATS
If the discharge valve seats merely show signs of slight
wear,theycanbedressedbyusingalappingstone,grinding
compound and grinding tool however it is recommended
that a cylinder head maintenance kit be used. Install new
dischargevalve springs andvalves. Screwin thedischarge
valve seats, and tighten to 70-90 ft.-lbs. Discharge valve
travel should be between .030 in. to .046 in. To test for
leakage by the discharge valves, apply 100 psi to the
cylinder head discharge port and apply a soap solution
to the discharge valve and seats. Leakage in the form of
soapbubbles ispermissible. If excessiveleakage isfound,
leave the air pressure applied and with the use ofa fiberor
hardwood dowel and a hammer, tap the discharge valves
offtheir seatsseveral times.This willhelp thevalvesto seat
and should reduce the leakage. With the air pressure still
applied at the discharge port of the cylinder head, check
for leakage around the discharge valve stop on the top of
the cylinder head casting. No leakage is permitted.
SIDE CLEARANCE
.000
.006
STANDARD PISTON
RING
.002
.004 OILRING
EXPANDER
RING
END GAP
.002
.013
.010
.040
Segment
Ring End
Gap
FIGURE 12 - RING CONFIGURATION
Compression

12
INLET VALVES AND SEATS
Inlet valves and springs should be replaced. However, if
theinlet valveseats show signsof slightnicks orscratches,
they can be redressed with a fine piece of emery cloth or
by lapping with a lapping stone, grinding compound and
grinding tool. If the seats are damaged to the extent that
they cannot be reclaimed, they must be replaced.
ASSEMBLY
General Note: All torques specified in this manual are
assembly torques and typically can be expected to fall off
after assembly is accomplished. Do not retorque after
initial assembly torques fall unless instructed otherwise.
A compiled listing of torque specifications is presented at
the end of this manual.
To convert inch pounds of torque to foot pounds of torque,
divide inch pounds by 12.
inch pounds ÷ 12 = foot pounds
To convert foot pounds of torque to inch pounds of torque,
multiply foot pounds by 12.
foot pounds x 12 = inch pounds
INSTALLING CRANKSHAFT
Press new sleeve bearings in the end cover and crank-
case. Ensure that the slot in the bearings line up with the
oil passages in the end cover or crankcase. If you have a
model with no oil passage present in the crankcase, press
the sleeve bearing into the crankcase with the slot located
90 degrees from vertical.
Install the front thrust washer with the tang inserted in
the slot toward the flange. Insert the crankshaft and the
rear thrust washer with the tang toward the rear of
the compressor.
Placethe oilseal ringon theboss ofthe rearend coverand
installthe end cover making surenot to pinchthe sealring.
Ensure the tang of the thrust washer is inserted in the slot
of the end cover. Fasten the end cover to the crankcase
with the four cover cap screws. Torque the cap screws to
175-225 inch pounds in a cross pattern.
PISTONS AND CONNECTING RODS
If the pistons are to be replaced ensure that the correct
pistons are being installed. Note that the pistons for the
Tu-Flo®750compressorare similartothose of otherBendix
compressor models but may be identified by the piston
diameterand thedistance to thecenter ofthe wristpin from
the top of the piston as shown in Figure 13.
PISTON RINGS
Check each ring end gap in a cylinder bore before installa-
tion.Place the ringin the topof the cylinder bore andusing
the piston, push the ring to the midpoint of the cylinder
bore and check the ring gap. If the end gaps are incorrect
either the wrong repair size has been purchased or the
compressor is worn beyond specification and should be
replaced.
FIGURE 13 - PISTON COMPARISON
2.78
2.17
1.06
1.25
OTHER BENDIX®
TU-FLO®AIR COMPRESSORS TU-FLO®750 AIR COMPRESSOR
PISTON COMPARISON
Installthe ringson thepistons perthe followinginstructions
starting at the center of the piston and moving outward.
1. Install the spacer and segment rings as follows. Place
the spacer ring (25) in the piston groove, the ends of
the spacer must butt and not overlap. Install the top
segment (24) by inserting one end above the spacer
in the ring groove, 120 degrees from the spacer ends
and wind the segment into position. Install the bottom
segment in the same manner beneath the spacer,
making sure the gap is staggered 120 degrees from
both the top ring segment and the spacer end gaps.
Before using be sure both painted ends of the spacer
are visible and butted. (Refer to Figure 14.)
FIGURE 14 - PISTON & RINGS
COMPRESSION RING (23)
SEGMENT RING (24)
SPACER RING (25)
SEGMENT RING (24)

13
2. Installthe compressionrings (23)in theproper grooves
with the “pip” mark toward the top of the piston. (Refer
to Figure 14.)
Checkthe ringside clearanceof eachring inthe pistonring
groove. (Refer to Figure 12.) If the side clearance is too
large, the piston ring groove is worn beyond specifications
and the piston must be replaced.
Rotate the piston rings in their respective groove so that
each end gap is at least 90 degrees from the previous
ring’s end gap.
Lubricate the wrist pin (22) and wrist pin bushing in the
connectingrod withengine oil.Assemblethe upperportion
of the connecting rods and the pistons with the wrist pins.
Insert the wrist pin buttons (28) in the ends of the wrist pin.
Lubricatethe pistonsand ringswith engineoil. Using aring
compression tool return the piston to the cylinder bore.
Turn the crankshaft so that one of its connecting rod
journals is in the downward, center position. Install
the crankshaft journal bearing segments (38) on the
connecting rod (37) and connecting rod cap (39). Tighten
theconnectingrod bolts(40)evenly andtorque to 150- 170
inch pounds. Install the other connecting rod and piston in
the same manner. It is recommended that new connecting
rod cap screws be used.
Beforereplacingthe cylinderheadonthe crankcaseensure
the correct pistons have been used by turning the crank-
shaftone completerevolution suchthat eachpiston moves
to its maximum upward stroke. At the maximum upward
stroke position each piston should move to the top of the
crankcase. If the piston does not approach the top of the
crankcasethe pistonis incorrect, and if notreplaced, could
result in compressor damage.
BASE PLATE OR BASE ADAPTER
Position the base plate or base adapter gasket (20) on the
crankcase and install the base plate or base adapter (21)
asmarked before disassembly.Tightenthe sixcap screws
(22),securing thecast ironbase adapterevenly toa torque
of175-225inch poundsforbase plateorcover inacrossing
pattern after first snugging all 6 screws.
CYLINDER HEAD
Place the cylinder head gasket (19) and cylinder head
on the compressor crankcase and install the six cylinder
headcap screws. Snugthe cylinder headcap screws prior
to torquing the cap screws to 300-360 in. Ibs. in a cross
pattern. Retorque the unloader cover cap screws to 170-
225 in. Ibs.
FINAL COMPRESSOR ASSEMBLY
Install all crankshaft keys making certain to support the
crankshaft to avoid bearing damage. Install the crankshaft
nut where applicable. When installing drive couplings or
gears, do not exceed 120 foot pounds torque on the
crankshaft nut.
Use covers, plugs, or masking tape to protect all ports if
compressor is not to be installed immediately. Protect the
ends of the crankshaft against damage by wrapping with
masking tape or friction tape.
TESTING REBUILT COMPRESSOR
Inorder toproperly testacompressor underoperating con-
ditions,atest rackforcorrect mounting,cooling, lubricating,
and driving the compressor is necessary. Such tests are
not compulsory if the unit has been carefully rebuilt by an
experienced person. A compressor efficiency or build up
test can be run which is not too difficult. An engine lubri-
cated compressor must be connected to an oil supply line
ofatleast 15P.S.I. pressure duringthe testandan oilreturn
line must be installed to keep the crankcase drained.
Connect to the compressor discharge port, a reservoir
with a volume of 1,500 cubic inches, including the volume
of the connecting line. With the compressor operating at
2,100 R.P.M., the time required to raise the reservoir(s)
pressure from 85 psi to 100 psi should not exceed 5
seconds. During this test, the compressor should be
checked for gasket leakage and noisy operation, as well
as unloader operation and leakage.
If the compressor functions as indicated reinstall on the
vehicle connecting all lines as marked in the disassembly
procedure.
TU-FLO®750 AIR COMPRESSOR SPECIFICATIONS
Average weight ........................................................... 53
Number of cylinders ...................................................... 2
Bore size ............................................................. 2.78 In.
Stroke ................................................................. 1.87 In.
Displacement at 1250 RPM ............................ 16.5 CFM
CFM Maximum recommended RPM ............ 2,400 RPM
Minimum coolant flow (water cooled) at
Maximum RPM ................................................. 2.5 GPM
Minimum RPM ..................................................... 5 GPM
Approximate horsepower required at
1250 RPM at 120 PSIG (naturally aspirated) ............ 3.2
Turbocharge limits
See Compressor Turbocharging Parameters
Maximum inlet air temperature .............................. 250°F
Maximum discharge air temperature ..................... 400°F
Minimum pressure required to unload
(naturally aspirated) ........................................... 60 PSIG

14
Minimum oil pressure required at
engine idling speed ............................................ 15 PSIG
Minimum oil pressure required at
maximum governed engine speed .................... 15 PSIG
Minimum discharge-line size ............................. 1/2" I.D.
Minimum coolant-line size ................................. 3/8" I.D.
Minimum oil-supply line size ............................ 3/16" I.D.
Minimum oil-return line size ............................... 1/2" I.D.
Minimum air-inlet line size .................................. 5/8” I.D.
Minimum unloader-line size ............................. 3/16" I.D.
TORQUE SPECIFICATIONS
Bolt, Nut or Screw ........................... Assembly Torque
(in. Ibs.)
Cylinder Head ..................................................300 - 360
Unloader Cover Plate ...................................... 175 - 225
Discharge Valve Seat ............ 840 - 1,080 (70-90 ft. Ibs.)
Inlet Valve Stop ...................... 840 - 1,080 (70-90 ft. Ibs.)
End Cover ........................................................ 175 - 225
Connecting Rod ............................................... 150 - 170
Bottom Cover ................................................... 175 - 225
Air Strainer ....................................................... 125 - 150
Inlet Fitting ....................................................... 175 - 225
Discharge Fitting .............................................. 175 - 225
Governor or Governor Adapter ........................ 175 - 225
Pipe Plugs
1/16 ...................................................................... 35 - 50
1/8 ...................................................................... 85 - 105
1/4 .................................................................... 130 - 170
3/8 .................................................................... 160 - 200
1/2 .................................................................... 200 - 270
Pipe Bushing
1/2 .................................................................... 175 - 225
Crankshaft Nut:
Marsden or Castle .......... 1,200 - 1,400 (100-120 ft. lbs.)
P/N 298125
(Metric Thread).................2,640 - 3,048 (220-254 ft. lbs.)
DIMENSIONAL DATA
Port Sizes
Water inlet .................................................. 1/2 - 14 NPT
Water outlet ................................................ 1/2 - 14 NPT
Air discharge ............................................... 1/2 - 14 NPT
Governor ..................................................... 1/8 - 27 NPT
Oil inlet (end cover) .................................... 1/8 - 27 NPT
Piston
(standard) ..................................................... 2.77825 in.
(.010 oversize) .............................................. 2.78825 in.
(.020 oversize) .............................................. 2.79825 in.
(.030 oversize) .............................................. 2.80825 in.
Cylinder bore
(standard) ....................................................... 2.7810 in.
(.010 oversize) ................................................ 2.7910 in.
(.020 oversize) ................................................ 2.8010 in.
(.030 oversize) ................................................. 2.8110 in.
MAINTENANCE KITS AND AVAILABLE SERVICE
PARTS
Cylinder Maintenance Kit.
Piston Ring Kit (standard and oversizes.)
Piston and Rod Kit (standard and oversizes.)
Crankshaft Bearing Kit.
Gasket & Seal Kit.
COMPRESSOR TROUBLESHOOTING
IMPORTANT:Thetroubleshooting contained inthis section
considers the compressor as an integrated component of
the overall air brake charging system and assumes that
an air dryer is in use. The troubleshooting presented will
covernotonly thecompressoritself, butalsoother charging
system devices as they relate to the compressor.
WARNING! PLEASE READ AND FOLLOW THESE
INSTRUCTIONS TO AVOID PERSONAL INJURY OR
DEATH:
When working on or around a vehicle, the following
general precautions should be observed at all times.
1. Parkthevehicleonalevelsurface,applytheparking
brakes,andalwaysblockthewheels. Alwayswear
safety glasses.
2. Stop the engine and remove ignition key when
workingunderoraroundthevehicle. Whenworking
in the engine compartment, the engine should be
shut off and the ignition key should be removed.
Where circumstances require that the engine be
in operation, EXTREME CAUTION should be used
to prevent personal injury resulting from contact
withmoving,rotating,leaking,heatedorelectrically
charged components.
3. Do not attempt to install, remove, disassemble
or assemble a component until you have read
and thoroughly understand the recommended
procedures. Useonlythepropertoolsandobserve
all precautions pertaining to use of those tools.
4. If the work is being performed on the vehicle’s
air brake system, or any auxiliary pressurized air
systems, make certain to drain the air pressure
from all reservoirs before beginning ANY work
on the vehicle. If the vehicle is equipped with an
AD-IS®airdryersystemoradryerreservoirmodule,
be sure to drain the purge reservoir.
5. Followingthevehiclemanufacturer’srecommended
procedures, deactivate the electrical system in a
manner that safely removes all electrical power
from the vehicle.
6. Never exceed manufacturer’s recommended
pressures.

15
7. Never connect or disconnect a hose or line
containing pressure; it may whip. Never remove
a component or plug unless you are certain all
system pressure has been depleted.
8. Use only genuine Bendix®replacement parts,
components and kits. Replacement hardware,
tubing, hose, fittings, etc. must be of equivalent
size, type and strength as original equipment and
bedesigned specifically for suchapplications and
systems.
9. Components with stripped threads or damaged
parts should be replaced rather than repaired. Do
notattemptrepairsrequiringmachiningorwelding
unless specifically stated and approved by the
vehicle and component manufacturer.
10. Prior to returning the vehicle to service, make
certain all components and systems are restored
to their proper operating condition.
11. For vehicles with Antilock Traction Control (ATC),
the ATC function must be disabled (ATC indicator
lampshouldbeON)priortoperforminganyvehicle
maintenance where one or more wheels on a drive
axle are lifted off the ground and moving.