BENDIX TU-FLO 750 User Manual
®
Bendix® Tu-Flo® 750 Air Compressor
SD-01-344
DISCHARGE
VALVE STOP
DISCHARGE
VALVE
DISCHARGE
VALVE SEA T
CRANKCASE
PISTON RINGS
CONNECTING
ROD
CRANKSHAFT
UNLOADER
COVER
DISCHARGE
VALVE SPRING
PISTON
BENDIX® TU-FLO® 750 AIR COMPRESSOR
(CROSS SECTION)
DESCRIPTION
The function of the air compressor is to provide and maintain 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.
AIR DISCHARGE
WATER
INLET
GOVERNOR
MOUNTING
PAD
CYLINDER
HEAD
CYLINDER
HEAD
WATER OUTLET
AIR INLET
CRANKCASE
PIECE NO.
TAG
BENDIX® TU-FLO® 750 AIR COMPRESSOR
(EXTERIOR)
UNLOADER
INLET V ALVE
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. Governor
mounting surfaces are provided at 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
750 compressor is designed such that the cylinder head
can be installed in one of two positions which are 180 degrees
apart. The crankcase houses the cylinder bores, pistons,
crankshaft and main bearings, and provides the flange or
base mounting surface.
INLET VALVE
SEAT
INLET
INLET V ALVE
®
SPRING
END VIEW OF CYLINDER HEAD
1
AIR DISCHARGE
UNLOADER COVER
PLATE
AIR
DISCHARGE
WATER
WATER
FIGURE 1 - CYLINDER HEAD
CAT MACK
(MACK STYLE)
MACK
EXTENDED
AIR INLET
GOVERNOR
MOUNTING
PAD
MACK
"FOXHEAD"
CUMMINS
WATER
DETROIT
DIESEL
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.)
TU-FLO 750 COMPRESSOR
BENDIX NO.
SERIAL NO.
MANUFACTURED BY BENDIX
FIGURE 3 - NAMEPLATE
OPERATION
The compressor is driven by the vehicle engine and is operating continuously while the engine is running. Actual
compression of air is controlled by the compressor unloading mechanism and the governor. The governor, which is
generally mounted on the compressor, maint ains the brake
2
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
created between the top of the piston and the cylinder head,
causing the inlet valve to move off its seat and open. (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 it s 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
DISCHARGE
DISCHARGE
VALVE
CLOSED
AIR
PORT
GOVERNOR
PORT
INLET
VALVE
OPEN
PISTON
MOVING
DOWN
AIR
INLET
PORT
DISCHARGE
VALVE
CLOSED
DISCHARGE
PORT
UNLOADER
PISTON
GOVERNOR
PORT
AIR
INLET
PORT
INLET V ALVE
HELD OPEN
BY UNLOADER
PISTON
FIGURE 4 - OPERATIONAL-LOADED (INTAKE)
DISCHARGE
VALVE
OPEN
AIR
DISCHARGE
PORT
GOVERNOR
PORT
INLET
VALVE
CLOSED
PISTON
MOVING
UP
AIR
INLET
PORT
FIGURE 5 - OPERATIONAL-LOADED (COMPRESSION)
air in the discharge 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 setting of the governor, the governor allows air to p ass from the
reservoir, through the governor and into the cavity above the
unloader pistons. The unloader pistons move down holding
the inlet valves off their seats (see Figure 6.) With the inlet
valves held off their seats by the unloader pistons, air is
pumped back and forth between the two cylinders, and the
discharge valves remain closed. When air pressure from the
reservoir drops to the cut-in setting of the governor, the gov-
FIGURE 6 - OPERATIONAL-UNLOADED
ernor 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 oil supply 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 either be eliminated prior to entering the air system or after they enter.
3
Discharge
Line
Optional “Ping” T ank
Air Dryer
The Air Brake Charging System supplies the
compressed air for the braking system as well as other air
accessories for the vehicle. The system usually consists
of an air compressor, governor, discharge line, air dryer,
and service reservoir.
Compressor
Governor
(Governor plus Synchro valve
for the Bendix
FIGURE 6A - SYSTEM DRAWING
®
DuraFlo™ 596
Compressor)
DUTY CYCLE
The duty cycle is the ratio of time the compressor spends
building air to the total engine running time. Air compressors are designed to build air (run "loaded") up to 25% of the
time. Higher duty cycles cause conditions that affect air
brake charging system performance which may require additional maintenance. Factors that add to the duty cycle
are: air suspension, additional air accessories, use of an
undersized compressor, frequent stops, excessive leakage
from fittings, connections, lines, chambers or valves, etc.
Refer to T able A in the Troubleshooting section for a guide to
various duty cycles and the consideration that must be given
to maintenance of other components.
COMPRESSOR INST ALLATION
Optional Bendix® PuraGuard® QC
™
Oil Coalescing Filter
Service Reservoir
(Supply Reservoir)
Reservoir Drain
The discharge line must maintain a constant slope down
from the compressor to the air dryer inlet fitting or 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 component
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.
While the original compressor installation is usually completed by the vehicle manufacturer, conditions of operation
and maintenance may require additional consideration. The
following presents base guidelines.
DISCHARGE LINE
The discharge line allows the air, water-vapor and 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 T able A in the Troubleshooting section) assumes
a compressor with a normal (less than 25%) duty cycle,
operating in a temperate climate. See Bendix and/or other
air dryer manufacturer guidelines as needed.
4
HOLE
THREAD
FIGURE 6B - DISCHARGE LINE SAFETY VALVE
DISCHARGE LINE TEMPERA TURE
COOLING
When the temperature of the compressed air that enters
the air dryer is within the normal range, the air dryer can
remove most of the charging system oil. If the temperature
of the compressed air is above the normal range, oil as oilvapor 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 p assed to the air brake
service (supply) reservoir. The oil droplets and the water
collected are automatically purged when the governor
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™ oil coalescing filter, designed to minimize
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 crankshaf t
allows oil to lubricate the connecting rod crankshaft 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.
Air flowing through the engine compartment from the action
of the engine’s fan and the movement of the vehicle assists
in cooling the compressor. Coolant flowing from the engine’ s
cooling system through connecting lines enters the head
and passes through internal passages in the cylinder head
and is returned to the engine. Proper cooling is important in
maintaining discharge air 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.
WATER
®
IN
WATER
OUT
WA TER OUT
WATER
OUT
OR
(1 PORT
ONL Y)
WATER
IN
OR
(1 PORT
ONL Y)
OIL
INLET
OIL
OUTLET
FIGURE 7 - LUBRICATION (BASE MOUNT MODEL SHOWN)
WATER
IN
FIGURE 8 - COOLING
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 vacuum
side (engine air cleaner) of the supercharger or
turbocharger.
3. Pressurized induction - Compressor inlet is connected
to the pressure side of the supercharger or turbocharger.
See the tabulated technical data in the back of this manual
for specific requirements for numbers 2 and 3 above.
®
5
If a previously unturbocharged compressor is being turbocharged, it is recommended that the inlet cavity screen
(238948) be installed with 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 CompressorR.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.
35
30
25
20
15
10
5
Inlet Pressure (PSIG)
0
270024002100180015001200900600
Compressor Speed (RPM)
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 T able A in the Troubleshooting section for a guide to
various considerations that must be given to the maintenance of the compressor and other related charging system
components.
Important Note: Review the warranty policy before performing any intrusive maintenance procedures. An extended
warranty may be voided if intrusive maintenance is performed
during this period.
6
POL YURETHANE SPONGE STRAINER
P APER AIR STRAINER DRY ELEMENT-PLEA TED
FIGURE 10 - STRAINERS
POLYURETHANE SPONGE STRAINER
Every month, 150 operating hours or 5,000 miles, whichever occurs first, remove and wash all of the parts. 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 the air strainer
gasket if the entire strainer is removed from the compressor
intake.
DRY ELEMENT - PLEATED PAPER STRAINER
OIL P ASSING
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 sure the filter is in position. Be sure to replace the
air strainer gasket if the entire air strainer is removed from
the compressor intake.
INT AKE ADAPTER
When the engine air cleaner is replaced: Some com-
pressors are fitted with compressor intake adapters, 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
engine air filter is changed, the compressor intake adapter
should be checked. If it is loose, remove the intake adapter ,
clean the strainer plate, if applicable, and replace the intake
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
evidence of restrictions and carboning. If excessive buildup
is noted, thoroughly clean or replace the affected parts 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
for internal clogging from rust scale. If coolant lines appear
suspicious, check the coolant flow and compare to the tabulated technical data present in the back of this manual.
Carefully inspect the air induction system for restrictions.
All reciprocating compressors currently manufactured will
pass a minimal amount of oil. Air dryers will remove the
majority of oil prior to entrance into the air brake 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 T ABLE 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 excessive oil
passing. The steps to be followed when using the BASIC
test are presented in APPENDIX A at the end of the
TROUBLESHOOTING section.
COMPRESSOR DRIVE
Every six months, 1,800 operating hours or 50,000 miles,
whichever occurs first, check for noisy compressor
operation, which could indicate a worn drive gear coupling,
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 depend-
ing upon the results of this inspection or experience,
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.
®
LUBRICATION
Every six months, 1,800 operating hours or 50,000 miles
whichever occurs first, check external oil supply and re-
turn lines, if applicable, for kinks, bends, or restrictions 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 lines
should slope as sharply as possible back to 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 oil
seepage and refer to the TROUBLESHOOTING section for
appropriate tests and corrective action.
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 from
85-100 psi in 25 seconds or less. This test is performed
with the engine operating at maximum recommended governed speed. The vehicle manufacturer must certify this
performance on new vehicles with appropriate allowances
for air systems with greater than the minimum required
reservoir volume.
7
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 V AL VE 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.
REMOV AL AND DISASSEMBL Y
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 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 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
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 seat s
(18), valves (17) and valve springs (16).
8
4. Remove the inlet valve stops (14), valves (17), valve seats
(11), valve springs (12) and gaskets (10). It is recommended that a tool such as a J-25447-B, produced by
Kent Moore Tool Division Roseville, Michigan phone
1-800-328-6657, be used to remove the inlet valve stop.
CLEANING OF PARTS GENERAL
All parts should be cleaned in a good commercial grade of
solvent and dried prior to inspection.
CYLINDER HEAD
CRANKCASE BOTTOM COVER OR ADAPTER
DISASSEMBLY
1. Remove the cap screws (22) securing the bottom 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) and their caps (39) to ensure correct reassembly .
The connecting rod and cap are a matched set therefore the
caps must not be switched or rotated end for end.
1. Remove the connecting rod bolts (40) and bearing caps
(39).
2. Push the pistons (26) with the connecting rods (37) attached out the top of the cylinder bore of the crankcase.
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)
and any burrs from the crankshaft where the key or keys
were removed. (Note: Through drive compressors 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. Remove the rear end cover (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. If the compressor has ball type main bearings, 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.
Remove carbon deposits from the discharge cavity and rust
and scale from the cooling cavities of the cylinder head body .
Scrape all foreign matter from the body surfaces and use
shop air pressure to blow the dirt particles from the cavities.
Clean carbon and dirt from the inlet and unloader passages.
Use shop air to blow the carbon and dirt deposits from the
unloader passages.
OIL P ASSAGES
Thoroughly clean all oil passages through the crankshaft,
crankcase, end covers, base plate or base 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 coolant
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
the crankcase hole should be .0003 in. tight to .0023 in.
loose. This is to maintain the correct fit. The compressor
must be replaced if the fit is too loose.
On compressors fitted with precision, sleeve main bearings,
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 micrometers or calipers. Cylinder bores which are scored or out of
round by more than .0005 in. or tapered more than .0005 in.
9
2
3
1
CYLINDER
HEAD
19
CRANKCASE
32
18
15
16
17
31
31
20
NAMEPLATE
30
38
4
5
6
23
23
24
25
7
24
8
26
9
28
27
23
24
10
11
25
24
35
12
13
14
37
33
32
36
29
34
32
BALL BEARING
(MACK EXTENDED
39
FLANGE)
40
21
22
FIGURE 11 - EXPLODED VIEW
ITEM QTY DESCRIPTION ITEM QTY DESCRIPTION ITEM QTY DESCRIPTION
1 6 Cylinder Head Cap Screws 1 5 2 Discharge Valve Stop 2 9 1 Crankshaft
2 4 Unloader Plate Cap Screws 1 6 2 Discharge V alve Spring 3 0 1 Crankshaft Key
3 4 Unloader Plate Lock Washers 1 7 2 Discharge Valve 3 1 2 Thrust Washer
4 1 Unloader Plate 18 2 Discharge V alve Stop 32 2 Sleeve (or Ball) Bearing
5 1 Unloader Plate Gasket 1 9 1 Cylinder Head Gasket 3 3 1 End Cover Seal
6 2 O-ring 20 1 Base Gasket 3 4 1 End Cover
7 2 Unloader 21 1 Base Plate 3 5 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 3 8 2 Conn. Rod Inserts (Sets)
11 2 Inlet Valve Seat 2 5 4 Expander Ring 3 9 2 Connecting Rod Caps
12 2 Inlet V alve 2 6 2 Piston 40 4 Connecting Rod Bolts
13 2 Inlet V alve Spring 27 2 Wrist Pin
14 2 Inlet V alve Stop 28 4 Wrist Pin Button
10
should be rebored or honed oversize. Oversized pistons 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 connecting
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 with the
rings installed in the cylinder bores. Refer to Figure 12 for
correct gap and groove clearances.
CRANKSHAFT
Check the crankshaft threads, keyways, tapered ends and
all machined and ground surfaces for wear, scores, or damage. Standard crankshaf t journals are 1.1242 in. - 1.1250 in.
in diameter. If the crankshaft journals are excessively scored
SIDE CLEARANCE
or worn or out of round and cannot be reground, the compressor must be replaced. Connecting rod bearing inserts
are available in .010 in., .020 in. and .030 in. undersizes for
compressors with reground crankshafts. Main bearing journals must be maintained so the ball bearings are a snug fit
or so that no 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
Used bearing inserts must be replaced. The connecting rod
and cap are a matched set and therefore the caps must not
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
A new cylinder head maintenance kit should be used 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 V AL VES, V ALVE ST OPS AND
SEATS
.002
EXPANDER
.004
STANDARD
PISTON
RING
END GAP
FIGURE 12 - RING CONFIGURA TION
RING
Compression
Segment
Ring
OIL RING
End
Gap
.002
.013
.010
.040
.000
.006
If the discharge valve seats merely show signs of slight wear ,
they can be dressed by using a lapping stone, grinding
compound and grinding tool however it is recommended that
a cylinder head maintenance kit be used. Install new
discharge valve springs and valves. Screw in the discharge
valve seats, and tighten to 70-90 ft.-lbs. Discharge valve travel
should be between .030 in. to .046 in. T o 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 soap bubbles is
permissible. If excessive leakage is found, leave the air
pressure applied and with the use of a fiber or hardwood
dowel and a hammer, tap the discharge valves of f their seats
several times. This will help the valves to 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.
11
INLET V AL VES AND SEA TS
PISTON RINGS
Inlet valves and springs should be replaced. However, if the
inlet valve seats show signs of slight nicks or scratches,
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 as-
sembly torques and typically can be expected to fall off
after assembly is accomplished. Do not retorque after ini-
tial assembly torques fall unless instructed otherwise. A
compiled listing of torque specifications is presented at the
end of this manual.
T o convert inch pounds of torque to foot pounds of torque,
divide inch pounds by 12.
inch pounds ÷ 12 = foot pounds
T o 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 crankcase.
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.
Place the oil seal ring on the boss of the rear end cover and
install the end cover making sure not to pinch the seal ring.
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 175225 inch pounds in a cross pattern.
PISTONS AND CONNECTING RODS
Check each ring end gap in a cylinder bore before installation. Place the ring in the top of the cylinder bore and using
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.
PISTON COMP ARISON
2.78
1.25
OTHER BENDIX
TU-FLO® AIR COMPRESSORS
FIGURE 13 - PISTON COMPARISON
®
TU-FLO® 750
AIR COMPRESSOR
Install the rings on the pistons per the following instructions
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.)
COMPRESSION RING (23)
SEGMENT RING (24)
SPACER RING (25)
1.06
2.17
If the pistons are to be replaced ensure that the correct
pistons are being installed. Note that the pistons for the
Tu-Flo® 750 compressor are similar to those of other Bendix
compressor models but may be identified by the piston
diameter and the distance to the center of the wrist pin from
the top of the piston as shown in Figure 13.
12
SEGMENT RING (24)
FIGURE 14 - PISTON & RINGS
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