BENDIX BA-921 COMPRESSOR-STD-CLOSED ROOM Mounting instructions

FIGURE 1 - BA-921 COMPRESSOR
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 BA-921 compressor is a
single cylinder reciprocating compressor with a rated dis-
placement of 15.8 cubic feet per minute at 1250 RPM.
The compressor consists of a water cooled cylinder head
and valve plate assembly and an air cooled integral
crankcase and cylinder block. The cylinder head is an
aluminumcastingwhichcontainstherequiredairandwater
ports as well as an unloader piston. The valve plate
assembly consists of laminated and brazed steel plates
whichincorporatevarious valve openings and channelsfor
UNLOADER
COVER DISCHARGE
PORT(2)
CRANKCASE
WATER
PORT
CRANKCASE
COVER
CYLINDER
HEAD
VALVEPLATE
ASSEMBLY
OILPORT
(APPLICATION SPECIFIC)
AIR INLET
PORT
WATER
PORT
GOVERNOR
CONNECTION
conductingairandenginecoolantintoandoutofthecylinder
head.
The discharge valves are part of the valve plate assembly.
Thecylinderhead,withthevalveplatecompriseacomplete
cylinderhead assembly.
Thecastironcrankcaseandcylinderblockassembly,houses
thepiston,connectingrod,crankshaftandrelatedbearings.
The BA-921 crankcase cover is stamped with information
identifyingthecompressormodel, customer piece number,
Bendixpiece number and serialnumber. See figure2.
WATER
PORT
(MAY BE
DRILLED ON
SOME
MODELS)
main local global operation trouble-
menu search search shooting
SD-01-676
BA-921BENDIXAIRPOWERCOMPRESSOR
UNLOADER
PISTON
CONNECTING
ROD
SPRING
CRANKSHAFT
PISTON
PISTON RINGS
VALVE PLATE ASSY.
CRANKCASE AND
CYLINDER BLOCK
CYLINDER HEAD
BALANCE
PISTON
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2
OPERATION
The compressor is driven by the vehicle engine and func-
tions continuously while the engine is in operation. Actual
compressionof air is controlledby the compressor unload-
ingmechanismoperatingin conjunction with agovernor. of the unloader piston and, along with the unloader piston
spring, holds the unloader piston against its seat on the
valveplate. See figures 5& 7.
NON-COMPRESSION OF AIR (UNLOADED)
When air pressure in the supply reservoir reaches the cut-
out setting of the governor, the governor delivers system
air to the compressor unloader port. Air entering the un-
loader port acts on the unloader piston causing it to move
away from its seat on the valve plate assembly. When the
FIGURE 2 - BA-921 CRANKCASE COVER
AIR INTAKE (LOADED)
During the piston down stroke, a vacuum is created in the
cylinder bore above the piston. The vacuum causes the
inletreed valve to flex open. Atmospheric airflows through
the open inlet valve and fills the cylinder bore above the
piston. See figures 4 & 7.
AIR COMPRESSION (LOADED)
When the piston reaches approximately bottom dead cen-
ter (BDC), the inlet reed valve closes. Air above the piston
istrappedbythe closed inlet reed valve andiscompressed
asthepistonbeginstomovetowardtopdeadcenter(TDC).
When air in the cylinder bore reaches a pressure greater
thanthat of the systempressure the discharge reedvalves
openandairflowsinto the discharge line and airbrakesys-
tem.
Air, during the compression stroke, flows into the hollow
centeroftheunloader piston through an opening intheend
of the piston. Compressed air acts on the interior surfaces
FIGURE 3 - BA-921 COMPRESSOR UNLOADER SYSTEM
COMPRESSOR
GOVERNOR
SUPPLY RESERVOIR
RESERVOIR
PORT
GOVERNOR
UNLOADER
PORT
FIGURE 4 - OPERATIONAL-LOADED (INTAKE)
PISTON MOVING DOWN
AIR INLET
PORT
INLET
VALVE
OPEN
AIR
DISCHARGE
PORT
DISCHARGE
VALVE
CLOSED
UNLOADER
PISTON
DOWN &
SEATED
VALVE
PLATE
UNLOADER
PORT
FIGURE 5 - OPERATIONAL-LOADED (COMPRESSION)
PISTON MOVING UP
AIR INLET
PORT
INLET
VALVE
CLOSED
AIR
DISCHARGE
PORT
DISCHARGE
VALVE
OPEN
UNLOADER
PISTON
DOWN &
SEATED
VALVE
PLATE
UNLOADER
PORT
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3
unloaderpiston is unseateda passage is opened between
thecylinderboreandtheairinletcavityinthecylinderhead.
Air compression ceases. See figures 6 & 7.
Asthe piston moves frombottom dead center (BDC)to top
dead center (TDC) air in the cylinder bore flows past the
unseated unloader piston, into the cylinder head inlet cav-
ity and out the inlet port. On the piston down stroke (TDC
to BDC) air flows in the reverse direction, from the inlet
cavitypastthe unseated unloader pistonand into the cylin-
der bore.
LUBRICATION
The vehicle's engine provides a continuous supply of oil to
the compressor. Oil is routed from the engine to the com-
pressor oil inlet. An oil passage in the crankshaft conducts
pressurized oil to precision sleeve main bearings and to
theconnecting rodbearings. Spray lubrication of the cylin-
der bores, connecting rod wrist pin bushings, and ball type
main bearings is obtained as oil is forced out around the
crankshaft journals by engine oil pressure. Oil then falls to
thebottom of the compressorcrankcase and isreturned to
the engine through drain holes in the compressor mount-
ing flange.
COOLING
Cooling fins are part of the crankcase/cylinder block cast-
ing.Coolantflowingfromtheenginecoolingsystem through
connectinglinesenters the head and passesthroughinter-
nalpassagesinthecylinderheadandvalveplateassembly
andisreturnedto the engine. Proper coolingisimportantin
maintainingdischargeairtemperaturesbelowthe maximum
recommended400degreesFahrenheit.Figure8illustrates
thevariousapprovedcoolantflowconnections.Seethetabu-
lated technical data in the back of this manual for specific
requirements.
PREVENTATIVE MAINTENANCE
ImportantNote:Reviewthewarrantypolicybeforeperform-
ing any intrusive maintenance procedures. An extended
warrantymaybevoidedifintrusivemaintenanceisperformed
duringthisperiod.
EVERY 6 MONTHS, 1800 OPERATING HOURS
OR AFTER EACH 50,000 MILES WHICHEVER OC-
CURS FIRST PERFORM THE FOLLOWING
INSPECTIONS AND TESTS.
FIGURE 7 - CYLINDER HEAD AND VALVE PLATE ASSY.
Cylinder Block Side of Valve Plate Assembly
Cylinder Head Side of Valve Plate Assembly
Air Inlet Slots
(2)
Valve Plate Assembly Side of Cylinder Head
Coolant
TransferSlots
AirInlet
Slots (2)
Discharge
Ports(4)
Unloader
Piston Bore InletReed
Valve/Gasket
Without Inlet Valve Inlet Reed Valve in Place
Alignment
PinHoles
Discharge
Ports(4)
UnloaderPiston
SeatingSurface
Discharge
Valves(2)
Coolant
TransferSlots
AirInlet
Cavity
Discharge
Cavity
UnloaderPiston
Bore
FIGURE 6 - OPERATIONAL-UNLOADED
AIR INLET
PORT
AIR
DISCHARGE
PORT
DISCHARGE
VALVE
CLOSED
VALVE
PLATE
PISTON MOVES
UP & DOWN
INLET
VALVE
CLOSED
UNLOADER
PISTON UP
&
UNSEATED
AIR FROM
GOVERNOR
UNLOADER
PORT
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AIR INDUCTION
TheBA-921compressorisdesignedforeither natural aspi-
ration (connection to the vacuum side of the engine's air
induction system) or turbocharging. When attached to the
pressure side of the turbocharger, pressure at the BA-921
inlet port must not exceed 45 psig. See the tabulated tech-
nical data in the back of this manual.
One of the single most important aspects of compressor
preventive maintenance is the induction of clean air. Since
the BA-921 is connected to the engine air cleaner, proper
periodic maintenance of the engine air filter eliminates the
needforseparatefiltermaintenance.
Inspect the compressor intake fittings, and the connecting
hoses each time engine air cleaner maintenance is per-
formed.
1. Inspect the intake hose adapters for physical damage.
Make certain to check the adapters at both ends of the
intake hose or tubing.
2. The intake hose clamps and tighten them if needed.
3. Inspecttheintakehoseorline for signs of drying, crack-
ing, chafing and ruptures and replace it if necessary.
COMPRESSOR COOLING
Inspectthecompressordischarge port, inlet cavity anddis-
charge line for evidence of restrictions and carboning. If
excessivebuildupis noted, thoroughly cleanor replace the
affectedparts.Since carbon buildup generallyindicates in-
adequate cooling, 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
coolantlinesappearsuspicious,checkthecoolantflowand
comparetothetabulatedtechnicaldata present in the back
of this manual. Carefully inspect the air induction system
forrestrictions.
LUBRICATION
Check the external oil supply line for kinks, bends, or re-
strictions to flow. Supply lines must be a minimum of 3/16"
I.D. Refer to the tabulated technical data in the back of this
manual for oil pressure minimum values.
COMPRESSOR DRIVE
Check for noisy compressor operation, which could indi-
cateexcessivedrivecomponentwear.Adjustand/orreplace
as necessary. Check all compressor mounting bolts and
retightenevenlyifnecessary.Checkforleakageandproper
unloadermechanism operation. Repair orreplace parts as
necessary.
COMPRESSOR UNLOADER & GOVERNOR
Test and inspect the compressor and governor unloader
system for proper operation and pressure setting.
1. Make certain the unloader system lines are connected
as illustrated in figure 3.
2. Cyclethecompressorthroughtheloadedandunloaded
cycleseveraltimes.Makecertainthatthegovernorcuts
out at its specified pressure (cut in should be approxi-
mately 15-20 psi less than cutout pressure). Adjust or
replace the governor as required.
3. Note that the compressor cycles to the loaded and un-
loadedconditionspromptly.Ifpromptactionisnotnoted,
repair or replace the governor and/or repair the com-
pressor unloader.
SERVICE TESTS
GENERAL
Thefollowingcompressoroperatingandleakagetests need
not be performed on a regular basis. These tests should
be performed when; it is suspected that leakage is sub-
stantiallyaffectingcompressorbuildupperformance,orwhen
it is suspected that the compressor is “cycling” between
theloadandunloadedmodesduetounloaderplungerleak-
age.
OPERATING TESTS
Compressor Performance
Vehicles manufactured after the effective date of FMVSS
121must have acompressor capable ofraising air system
pressure from 85-100 psi in 25 seconds or less, with the
FIGURE 8- TYPICAL BA-921 CYLINDER HEAD
CYLINDER HEAD PORT IDENTIFICATION
The cylinder head connection ports are identified with cast
in numerals as follows:
Atmospheric AIR IN 0
Compressed AIR OUT 2
Coolant IN or OUT 9
Governor Control 4
COOLANT IN OR OUT
(ONE OR OTHER NOT USED)
GOVERNOR
CONNECTION
DISCHARGE
SAFETY VALVE
DISCHARGE
PORT
INLET
PORT
UNLOADER
COVER
COOLANT IN OR OUT
(ONE OR OTHER NOT USED)
HEAD
BOLT (4)
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5
minimumrequiredreservoirvolumeforthevehicle.Thistest
isperformedwiththeengine operating at maximum recom-
mended 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. As a less severe alternative to
runninga high RPM test, a new compressor'sbuildup time
can be measured and recorded at high idle. Subsequent
testingthroughoutthecompressor’sservice lifecanbecom-
pared to the base line new compressor performance.
Compressorbuilduptimesshouldberecordedandkeptwith
the vehicle maintenance files for reference. When testing
compressor buildup times it is essential that air system
leakagebekeptbelowtheallowedmaximumforthevehicle
type being tested. Before running buildup tests check the
service and supply systems for excessive leakage and re-
pair as necessary.
Note: Supplysystem leakage is not displayed
onthevehicledashgaugesandmust be tested
separately. Supply system components such
asthegovernor,airdyer,reservoirdraincocks,
safety valve and check valves can leak with-
out indication on the dash gauges. These
components must be checked for leakage
separately and individually. Refer to the vari-
ous maintenance manuals for individual
componentleakagetestsandtheBendix “Test
andChecklist” published in the AirBrake Sys-
temHandbook(BW5057)forairsystemleakage
testing.
LEAKAGE TESTS
Cylinder Head
Checkfor cylinder headgasket air leakage.
1. With the engine running, lower air system pressure to
60 psi and apply a soap solution around the cylinder
head.Checkthe gasket between the cylinderheadand
valveplateassemblyand thereedvalve/gasketbetween
thevalveplate assembly and cylinder blockforair leak-
age.
2. No leakage is permitted. If leakage is detected replace
thecompressororrepairthe cylinderheadusingagenu-
ineBendixmaintenancekitavailablefromanauthorized
Bendix parts outlets.
Unloader
In order to test the inlet and discharge valves and the un-
loaderpiston,it is necessary tohaveshop air pressure and
an assortment of fittings. A soap solution is also required.
Build-Uptests
1. With the engine running, lower air system pressure to
90 psi and raise engine RPM to 1800. Measure and
record the time required to raise system pressure from
100psi to130 psiRun thistest three times and use the
average time.
Note:Thistestshouldberunwiththeengineandair
systematnormaloperatingtemperature(i.e.notcold).
2. Comparetheaveragetimerecordedinstep2withprevi-
ously recorded build up times to evaluate compressor
performance.
Unloader leakage is exhibited by excessive compressor
cycling between the loaded and unloaded condition.
1. Withserviceandsupplysystemleakage belowthemaxi-
mum allowable limits and the vehicle parked, bring
system pressure to governor cutout and allow the en-
gine to idle.
2. Thecompressorshouldremainunloadedforaminimum
of5-10minutes. If compressor cyclingoccursmore fre-
quentlyandserviceandsupplysystemleakageiswithin
tolerancereplacethecompressoror repairthecompres-
sor unloader system using a genuine Bendix
maintenancekitavailable from authorized Bendix parts
outlets.
COMPRESSOR REMOVAL & DISASSEMBLY
GENERAL
Thefollowingdisassembly and assembly procedure ispre-
sentedforreferencepurposesandpresupposesthatarebuild
or repair of the compressor is being undertaken. Several
maintenancekitsareavailableandtheinstructions provided
with these parts and kits should be followed in lieu of the
instructionspresentedhere.
MAINTENANCE KITS & SERVICE PARTS
Cylinder Head Gasket Kit.
UnloaderKit.
GovernorAdapterKit.
SafetyValve.
Seal Kits.
All components shown in figure 9 with a key number are
available in kits and/or as individual service parts.
IMPORTANT! PLEASE READ:
When working on or around a vehicle, the following
general precautions should be observed:
1. Park the vehicle on a level surface, apply the park-
ing brakes, and always block the wheels.
2. Stop the engine when working around the vehicle.
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6
3. If the vehicle is equipped with air brakes, make
certain to drain the air pressure from all reservoirs
before beginning any work on the vehicle.
4. Following the vehicle manufacturer’s recom-
mended procedures, deactivate the electrical
system in a manner that removes all electrical
power from the vehicle.
5. When working in the engine compartment the en-
gine should be shut off. Where circumstances
require that the engine be in operation, extreme
caution should be used to prevent personal injury
resulting from contact with moving, rotating, leak-
ing, heated, or electrically charged components.
6. Never connect or disconnect a hose or line con-
taining pressure; it may whip. Never remove a
component or plug unless you are certain all sys-
tem pressure has been depleted.
7. Never exceed recommended pressures and always
wear safety glasses.
8. Do not attempt to install, remove, disassemble or
assemble a component until you have read and
thoroughly understand the recommended proce-
dures. Use only the proper tools and observe all
precautions pertaining to use of those tools.
9. Use only genuine Bendix replacement parts, com-
ponents, and kits. Replacement hardware, tubing,
hose,fittings,etc.shouldbeof equivalent size, type,
andstrengthasoriginalequipmentand be designed
specifically for such applications and systems.
10.Components with stripped threads or damaged
parts should be replaced rather than repaired. Re-
pairs requiring machining or welding should not
be attempted unless specifically approved and
stated by the vehicle or component manufacturer.
11. Prior to returning the vehicle to service, make cer-
tain all components and systems are restored to
their proper operating condition.
REMOVAL
In many instances it may not be necessary to remove the
compressor from the vehicle when installing the various
maintenancekitsandserviceparts.Themaintenancetech-
nicianmustassesstheinstallationanddeterminethecorrect
courseof action.
Theseinstructionsaregeneralandareintendedtobeaguide.In
somecasesadditionalpreparationsandprecautionsareneces-
sary. In all cases follow the instructions contained in the vehicle
maintenancemanualin lieu of theinstructions,precautions and
procedurespresented inthis manual.
1. Block the wheels of the vehicle and drain the air pres-
sure from all the reservoirs in the system.
2. Drain the engine cooling system and the cylinder head
ofthecompressor. Identify anddisconnect all air,water
and oil lines leading to the compressor.
3. Remove as much road dirt and grease from the exte-
rior of the compressor as possible.
4. Remove the discharge and inlet fittings, if applicable, and
note their position on the compressor to aid in reassembly.
Note: If a cylinder head maintenance kit is being
installed, stop here and proceed to
PREPARATION FOR DISASSEMBLY. If
replacing the compressor continue.
3. Remove any supporting bracketing attached to the
compressorandnotetheir positions on the compressor
to aid in reassembly.
5. Removetheflangemountingboltsandremovethe com-
pressor from the vehicle.
6. Inspectgearand associated drive partsforvisible wear
or damage. Since these parts are precision fitted, they
must be replaced if they are worn or damaged. If re-
placing the compressor or replacing the drive gear,
removethe drivegear from the compressor crankshaft
usingagear puller.
7. If the compressor is being replaced stop here and pro-
ceed to "Installing The Compressor" at the end of the
assemblyprocedure.
PREPARATION FOR DISASSEMBLY
Removethe balance of road dirt and greasefrom the exte-
rior of the compressor with a cleaning solvent. Mark the
rearendcoverorendcoveradapter in relation to the crank-
case. It is recommended but not specifically necessary to
marktherelationship of the cylinderheadto the valve plate
assembly and crankcase and cylinder block assembly.
Aconvenient method toindicate the aboverelationships 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.
Priorto disassembly make certain that the appropriate kits
and or replacement parts are available. Refer to figure 9
during the entire disassembly and assembly procedure.
CYLINDER HEAD
1. Removethedischarge safety valve (10) from the cylin-
der head.
2. To restrain the spring force exerted by balance piston
spring (5), hold the unloader cover (2) in place while
removingthetwo unloader cover capscrews (1). Care-
fully release the hold on the unloader cover until the
springforceisrelaxed, then remove the unloadercover
(2).
3. Remove the unloader cover gasket (3).
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FIGURE 9- BA-921 EXPLODED VIEW OF SERVICEABLE PARTS
Valve Plate Assembly
Item Qty. Description Item Qty. Description Item Qty Description
1 2 Unloader Cover Cap Screw 6 1 O-Ring 11 1 Head Gasket
2 1 Unloader Cover 7 1 O-Ring 12 -- Intentionally Left Blank
3 1 Unloader Cap Gasket 8 1 Unloader Piston 13 1 Inlet Reed Valve/Gasket
4 1 Unloader Balance Piston 9 1 O-Ring 14 1 O-Ring
5 1 Spring 10 1 Safety Valve 15 1 Bottom Cover Gasket
CRANKCASE
COVER
CRANKCASE
&
CYLINDER
BLOCK
CYLINDER
HEAD
12
7
8
END COVER
4
6
9
10
3
5
CRANKCASE
SCREW
15
END COVER
SCREW
13
11
14
¶
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4. Remove the balance piston (4) and its spring (5) from
the cylinder head.
5. Remove the four hex head bolts and washers from the
cylinderhead.
6. Gently tap the head and valve plate assembly with a
soft mallet to break the gasket seal. Lift the cylinder
head and valve plate assembly (12) off the cylinder
block.
7. Remove the metal reed valve/gasket (13).
8. Gentlytap the head andvalve plate assembly(12) with
a soft mallet to break the gasket seal. Then separate
the cylinder head from the valve plate assembly (12)
andremovethegasket(11).
9. Turnthealuminum cylinder head overtoexpose the in-
terior portion of the head. Push the unloader piston (8)
alongwith its o-rings(6, 7 &9) out ofthe cylinder head.
CRANKCASE COVER
1. Removethefour crankcase cover capscrews securing
thecrankcasecovertothecrankcase. Using a soft mal-
let, gently tap the crankcase cover to break the gasket
seal.Removethe crankcase cover gasket(15).
REAR END COVER OR END COVER ADAPTER
1. Removethe four endcover cap screws that securethe
rear end cover or end cover adapter to the crankcase.
2. Remove the rear end cover or end cover adapter from
the crankcase. Remove the o-ring seal (14) from the
end cover.
CLEANING OF PARTS
GENERAL
All parts should be cleaned in a good commercial grade of
solvent and dried prior to inspection.
CYLINDER HEAD
1. Carefully remove all gasket material adhering to the
aluminumcylinderhead,steelvalveplateassemblyand
cast iron cylinder block. Make certain not to deeply
scratch or mar the gasket surfaces. Pay particular at-
tention to the gasket surfaces of the aluminum head.
2. Remove carbon deposits from the discharge and inlet
cavities of the cylinder head and valve plate assembly.
Theymustbeopen and clear in bothassemblies.Make
certain not to damage the aluminum head.
3. Remove rust and scale from the cooling cavities and
passages in the head and valve plate assembly (12)
and use shop air to clear debris from the passages.
4. Check the threads in all cylinder head ports for galling.
Minor chasing is permitted.
5. Make certain the unloader vent passage under the un-
loader cover (2) in the head is open and free of debris.
INSPECTION OF PARTS
CYLINDER HEAD & VALVE PLATE
1. Carefully inspect the cylinder head gasket surfaces for
deep gouges and nicks. If detected, the compressor
must be replaced.
2. Carefully inspect the valve plate assembly gasket sur-
facesfordeepgouges andnicks.Payparticularattention
tothemetalgasketsurface. A metal gasket (18) is used
between the valve plate assembly and cylinder block.
Thissurfacemustbesmoothandfreeofallbutthemost
minorscratching.Ifexcessivemarring or gouging is de-
tected, the compressor must be replaced.
3. Inspect the cylinder head for cracks or damage. With the
cylinder head and head gasket secured to the valve plate
assembly,applyshopairpressuretooneofthecoolantports
withallothersplugged,andcheckforleakagebyapplyinga
soap solution to the exterior of the head. If leakage is de-
tectedinthecylinderheadcasting,replacethecompressor.
END COVER OR END COVER ADAPTER
Checkforcracksandexternaldamage.Checkthecrankshaft
mainbearingsurfaceintheendcoverorendcoveradapter,
checkforexcessivewearandflatspotsandreplacetheend
cover if necessary. Check for galling of the oil port threads
andreplacetheendcoverorendcoveradapterifnecessary.
Minor thread chasing is permitted but do not “recut” the
threads if they are badly damaged.
CYLINDER BLOCK
1. Checkthe cylinder head gasketsurface on the cylinder
blockfor nicks, gouges,and marring. A metal gasketis
used to seal the cylinder head to the cylinder block.
This surface must be smooth and free of all but the
most minor scratching. If excessive marring or goug-
ing is detected, the compressor 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 re-torque after
initial assembly torques fall unless instructed otherwise. A
compiledlisting of torque specificationsis presented atthe
end of this manual.
INCH POUNDS TO FOOT POUNDS
To convert inch pounds to foot pounds of torque, divide
inch pounds by 12.
Example: 12 Inch Pounds = 1 Foot Pound
12
FOOT POUNDS TO INCH POUNDS
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To convert foot pounds to inch pounds of torque, multiply
foot pounds by 12.
Example: 1 Foot Pound x 12 = 12 Inch Pounds
CRANKCASE COVER
1. Position the crankcase cover gasket (15) on either the
crankcase or crankcase cover and install the crank-
casecoveronthecrankcaseusingthe four cap screws.
"Snug" the four cap screws then torque to 62-71 inch
pounds using a crossing pattern.
CRANKCASE END COVER OR ADAPTER
1. Install the end cover o-ring (14) on the crankcase end
cover.
2. Orient the crankcase end cover or end cover adapter
to the crankcase using the reference marks made dur-
ing disassembly. Carefully install the end cover or end
cover adapter in the crankcase making certain not to
damage the crankshaft bearing surface in it.
3. Install the four end cover screws or studs. "Snug" the
screws then tighten to 195 to 213 inch pounds using a
crossing pattern.
CYLINDER HEAD
1. Notethepositionoftheprotrudingalignmentpinsonthe
cylinder block. Install the metal inlet reed valve/gasket
(13)over the alignment pins on the cylinder block.
2. Position the valve plate assembly (12) on the cylinder
block so that the alignment pins in the cylinder block fit
into the corresponding holes in the valve plate assem-
bly (12).
3. Positionandinstallthe metal gasket (11) overthealign-
mentbushingsprotrudingfromthevalveplateassembly
(12). Whenproperly installed, theoutline of the gasket
matches the outline of the valve plate.
4. Position and install the cylinder head over the align-
mentbushingsprotrudingfromthevalveplateassembly
(12).
Note: The alignment bushings will only fit into
two of the four cylinder head bolt holes.
5. Install the four hex head cylinder head bolts and wash-
ers and snug them, then tighten evenly to a torque of
265 to 292 inch pounds using a crossing pattern.
6. Install the unloader piston (8) with its pre-installed o-
ringsinthecylinderhead making certain not todamage
them in the process.
7. Installthebalance piston spring(5) in theunloader pis-
ton (8), then install the small diameter of the balance
piston (4) through the center of the spring.
8. Installtheunloadercovergasket(3)onthecylinderhead
making certain the unloader vent passage and both
screw holes align.
9. Position the unloader cover (2) on top of the balance
piston (4) making certain the stamped logo is visible.
10. Press and hold the unloader cover (2) in place on the
cylinderheadandinstallbothunloadercovercapscrews
(1). Torque the cover cap screws (1) to 62 to 71 inch
pounds.
INSTALLING THE COMPRESSOR
1. Ifthecompressor was removed forreplacement, install
the drive components. Torque the crankshaft nut to
250 foot pounds.
2. Install any supporting bracketing on the compressor in
the same position noted and marked during removal.
3. Install the gasket on the drive flange of the compres-
sor.Makecertain oil supply or return holes in thegasket
are properly aligned with the compressor and engine.
Gasket sealants are not recommended. Secure the
compressor on the engine and tighten the mounting
bolts.
4. Installthedischarge,inletandgovernoradapterfittings,
if applicable, in the same position on the compressor
noted and marked during disassembly. Make certain
the threads are clean and the fittings are free of corro-
sion. Replace as necessary. See the Torque
Specificationsforvariousfittingsizesandtypesofthread
at the rear of this manual.
5. Inspect all air, oil, and coolant lines and fittings before
reconnecting them to the compressor. Make certain o-
ringsealsareingoodor new condition. Tightenallhose
clamps.
6. Clean oil supply line. Before connecting this line to the
compressor.Runtheenginebrieflytobesureoilisflow-
ing freely through the supply line.
7. Before returning the vehicle to service, perform the
Operation and Leakage Tests specified in this manual.
Pay particular attention to all lines reconnected during
installation and check for air, oil, and coolant leaks at
compressor connections. Also check for noisy opera-
tion.
TESTING REBUILT COMPRESSOR
Inordertoproperlytest a compressor under operatingcon-
ditions,atestrackforcorrectmounting,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
of at least 15 psi. pressure during the test and an oil return
line must be installed to keep the crankcase drained. Con-
nect to the compressor discharge port, a reservoir with a
volume of 1500 cubic inches, including the volume of the
connecting line. With the compressor operating at 2100
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10
RPM., the time required to raise the reservoir(s) pressure
from 85 psi to 100 psi should not exceed 5 seconds. Dur-
ingthis test,the compressor should be checked for gasket
leakage and noisy operation, as well as unloader opera-
tion and leakage. If the compressor functions as indicated
reinstall on the vehicle connecting all lines as marked in
the disassembly procedure.
BA-921 SPECIFICATIONS
Typicalweight ....................................................... 28 lbs.
Numberofcylinders ...................................................... 1
BoreDiameter ....................................... 92mm(3.622 in.)
Stroke ................................................... 54 mm(2.125 in.)
Calculateddisplacement at 1250 RPM............. 15.8 CFM
Flow Capacity @ 1800 RPM & 120 PSI ............ 11.8 CFM
Flow Capacity @ 3000 RPM & 120 PSI ............18.0CFM
MaximumrecommendedRPM ........................ 3000 RPM
Minimumcoolant flow maximumRPM ...... 1.3 Gals./Min.
Approximatehorsepowerrequired:
Loaded1800RPM at 120PSIG ........................... 4.5 HP
Unloaded1800RPM ............................................ 1.3 HP
Maximuminletair temperature .............................. 250 F°
Maximumdischargeairtemperature ..................... 400 F°
Minimumoilpressure required at
engineidlingspeed ............................................... 15 PSI
Minimumoilpressure required at
maximumgovernedenginespeed ......................... 15 PSI
Minimum oil-supply line size ............................. 3/16" I.D.
Minimumunloader-linesize............................... 3/16" I.D.
MinimumGovernorCutoutPressure .......................90PSI
TORQUE SPECIFICATIONS
Assembly Torques in inch pounds (in. Ibs.)
M8x1.25-6gCylinderHead .................................265-292
M5x0.75-6gUnloaderCap ..................................... 62 - 71
M8x1.25-6gGovernorAdapter ............................133-142
M8x1.25-6gRearEndCover...............................195-213
M6x1.00-6gCrankcaseCover............................... 62 - 71
M20x2.50-6gCrankshaftNut ......................... 1858- 2567
Inlet Port Fittings
7/8"-12UNF .......................................................221-248
3/4"-14NPT .................................................... 2-3TFFT1
DischargePort Fittings
7/8"-12UNF .......................................................221-248
3/4"-14NPT .................................................... 2-3TFFT1
Water Port Fittings
3/4"-16UNF .......................................................221-248
3/8"-18NPT .................................................... 2-3TFFT1
UnloaderPortFittings
1/8"-27NPT .................................................... 2-3TFFT1
SafetyValvePort
3/4"-16UNF .......................................................221-248
1/2"-14NPT .................................................... 2-3TFFT1
OilPort 7/16"-16 UNF ........................................177 -204
1Note:TFFT=Turns From Finger Tight
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11
1. Compressor passes A. Restricted air intake. A. Check engine air cleaner and replace if
excessiveoilasevidenced necessary. Check compressor air inlet for kinks,
by presence of oil at excessivebends andbecertaininletlines have
the exhaust ports of minimumspecifiedinsidediameter.Recommended
valving. maximum air inlet restriction is 25" of water.
B. Restricted oil return to B. Oil return to the engine should not be in any way
engine. restricted. Make certain oil drain passages in the
compressor and mating engine surfaces are
unobstructed and aligned. Correct gaskets must
be used. Special care must be taken when seal
ants are used with, or instead of, gaskets.
C. Poorly filtered inlet air. C. Check for damaged, defective or dirty air filter on
engine or compressor. Check for leaking, damaged
or defective compressor air intake components
(e.g. induction line, fittings, gaskets, filter bodies,
etc.). The compressor intake should not be
connected to any part of the exhaust gas
recirculation (E.G.R.) system on the engine.
D. Insufficientcompressor D.Forwater-cooled portions ofthecompressor:
cooling(compressorruns 1. Check for proper coolant line sizes. Minimum
hot). recommended size is 3/8" I.D. tubing.
2. Checkthecoolantflowthroughthecompressor.
Minimum allowable flow is 2.5 gallons per
minute at engine governed speed. If low cool
ant flow is detected, inspect the coolant lines
and fittings for accumulated rust scale, kinks
and restrictions.
3. Water temperature should not exceed 200
degreesFahrenheit.
4. Optimum cooling is achieved when engine
coolant flows, as shown in Figure 8 of this
manual.
E. Contaminants not being E. Check reservoir drain valves to insure that they
regularly drained from are functioning properly. It is recommended that
system reservoirs. the vehicle should be equipped with functioning
automatic drain valves, or have all reservoirs
drained to zero (0) psi daily, or optimally to be
equipped with a desiccant-type air dryer prior to
the reservoir system.
COMPRESSOR TROUBLESHOOTING CHART
SYMPTOMS CAUSE REMEDY
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12
COMPRESSOR TROUBLESHOOTING CHART (Continued)
SYMPTOMS CAUSE REMEDY
1. (Continued.) F. Compressor runs loaded F. Vehicle system leakage should not exceed indus-
an excessive amount of try standards of 1 psi pressure drop per minute
time. without brakes applied and 3 psi pressure drop
per minute with brakes applied. If leakage is
excessive, check for system leaks and repair.
G. Excessive engine G. Test for excessive engine crankcase pressure &
crankcase pressure. replace or repair ventilation components as
necessary. (An indication of crankcase pressure
is a loose or partially lifted dipstick.)
H. Excessive engine oil H. Check the engine oil pressure with a test gauge
pressure. andcompare the reading tothe engine specifica-
tions. Bendix does not recommend restricting the
compressor oil supply line because of the
possibility of plugging the restriction with oil
contaminants. Minimum oil supply line size is
3/16" I.D. tubing.
I. Faultycompressor. I. Replace or repair the compressor only after
making certain none of the preceding installation
defects exist.
2. Noisycompressor A. Loosedrivegearor A..Inspectthefit of the drive gear onthe compres-
operation. components. sorcrankshaft. The gearor coupling mustbe
completely seated and the crankshaft nut must
be tight. If the compressor crankshaft surface is
damaged, it is an indication of loose drive
components. If damage to the compressor
crankshaft is detected, replace the compressor.
When installing the drive gear or pulley, torque
the crankshaft nut to the appropriate torque
specifications and use care when pressing drive
components onto the crankshaft.
Do not back off the crankshaft nut once it is
tightened to the proper torque.
Do not use impact wrenches to install the
crankshaft nut.
B. Excessively worndrive B. Inspect drive gear and couplings and engine for
couplings or gears. excessive wear. Replace as necessary.
(Nonmetallic gears should be replaced when the
compressor is changed.)
C. Compressor cylinder head C. Inspect the compressor discharge port and
or discharge line discharge line for carbon build-up. If carbon is
restrictions. detected, check for proper cooling to the
compressor. (See Cause and Remedy (D) under
Symptom #1.) Inspect the discharge line for kinks
and restrictions. Replace discharge line as
necessary.
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13
COMPRESSOR TROUBLESHOOTING CHART (Continued)
2. (Continued.) D. Wornor burned out D. Checkforproperoilpressure in the compressor.
bearings. Minimum required oil pressure; 15 psi engine
idling, 15 psi maximum governed engine rpm.
Check for excessive oil temperature—should not
exceed 240 degrees Fahrenheit.
E. Faulty compressor. E. Replace or repair the compressor after
determining none of the preceding installation
defects exist.
3. Excessive build-up and A. Dirty induction air filter. A. Inspect engine or compressor air filter and
recover time. Compressor replace if necessary.
should be capable of
building air system from B. Restricted induction line. B. Inspect the compressor air induction line for kinks
85-100 psi in 40 seconds and restrictions and replace as necessary.
with engine at full
governed rpm. Minimum C. Restricted discharge line C. Inspect the compressor discharge port and line
compressor performance or compressor discharge for restrictions and carbon build-up. If a carbon
is certified to meet Federal cavity. build-up is found, check for proper compressor
requirements by the cooling. Replace faulty sections of the discharge
vehicle manufacturer. Do line.
not downsize the original
equipment compressor. D. Slipping drive components. D. Check for faulty drive gears and couplings and
replace as necessary. Check the condition of
drive belts and replace or tighten, whichever is
appropriate.
E. Excessive air system E. Test for excessive system leakage and repair as
leakage. necessary. Use the following as a guide: Build
system pressure to governor cutout and allow the
pressure to stabilize for one minute. Using the
dash gauge, note the system pressure and the
pressuredropafter two minutes.
Thepressuredrops should not exceed:
1. 2 psi in each reservoir for a single vehicle.
2. 6 psi in each reservoir for a tractor and trailer.
3. 8 psi in each reservoir for a tractor and 2
trailers.
F. Stickingunloaderpistons. F. Checktheoperationof the unloading mechanism.
Checkforproperoperation of the compressorair
governor.Make certain the air connections
betweenthegovernorandcompressorare
correct.Referto figure 3. Ifthe governor is
operatingproperly,replacetheunloader
mechanism. Inspect for bent, linked or blocked
tubingleadingtoorfromthegovernor.
G. Faulty compressor. G. Replace or repair the compressor after
determining none of the preceding installation
defects exist.
SYMPTOMS CAUSE REMEDY
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14
COMPRESSOR TROUBLESHOOTING CHART (Continued)
SYMPTOMS CAUSE REMEDY
4. Compressor fails to A. Faulty governor or A. Test the governor for proper operation and
unload. installation. inspect air lines to and from it for kinks or
restrictions. Replace or repair the governor or
connecting air lines
B. Faulty or worn unloader B. Inspect for worn, dirty or corroded unloader
pistons or bores. piston and bore. Replace as necessary.
5. Compressor leaks oil. A. Damaged mounting gasket. A. Check the compressor mounting bolt torque. If
the mounting bolt torque is low, replace the
compressor mounting gasket before re-torquing
the mounting bolts.
B. Cracked crankcase or end B. Visually inspect the compressor exterior for
cover. cracked or broken components. Cracked or
broken crankcases or mounting flanges can be
caused by loose mounting bolts. The end cover
can be cracked by over-torquing fitting or plugs
installed in the end cover. Replace or repair the
compressor as necessary.
C. Loose crankcase end C. Check the cap screw torques and tighten as
cover or bottom cover. necessary. Replace gaskets or o-ring.
D. Loose oil supply or return D. Check the torque of external oil line fittings and
line fittings. tighten as necessary.
E. Porous compressor casting. E. Replace the compressor if porosity is found.
F. Mounting flange or end F. Replace as necessary.
cover, o-ring or gasket
missing, cut or damaged.
6. Compressor constantly A. Leaking compressor A. Repair or replace as necessary. Remove the
cycles (compressor unloader piston. compressor inlet air strainer or fitting. With the
remains unloaded for a compressor unloaded (not compressing air),
very short time). listen for air escaping.
B. Faulty Governor installation. B. Test the governor for proper operation and
inspect air lines for kinks or restrictions. Replace
or repair the governor or connecting air lines as
required.
C. Excessive system leakage. C. Test for excessive system leakage as instructed
in Symptom #3 Remedy E. Reduce leakage
whereverpossible.
D. Excessive reservoir D. Drain reservoirs.
contaminants.
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15
COMPRESSOR TROUBLESHOOTING CHART (Continued)
SYMPTOMS CAUSE REMEDY
7. Compressorleaks A. Improperlyinstalledplugs A. Check torque of fittings and plugs and tighten as
coolant. and coolant line fittings. necessary. Over torqued fittings and plugs can
crack the head or block casting.
B. Freeze cracks due to B. Test antifreeze and strengthen as necessary.
improper antifreeze Check coolant flow through compressor to as
strength. sure the proper antifreeze mixture reaches the
compressor.
C. Faultycompressor C. If casting porosity is detected, replace the com-
(porouscastings). pressor.
8. Compressor head A. Restricted discharge line. A. Clear restriction or replace line.
gasket failure.
B. Loose head bolts B. Tighten evenly to a torque of 265-292 inch
pounds.
C. Faulty compressor or head C. Check for rough or poorly machined head or
gasket. block surfaces. Replace compressor as
necessary.
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16 BW2158 © Honeywell Commercial Vehicle Systems Company 4/2001. Printed in USA.
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