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This service data sheet covers two versions of the Bendix
compressor. The fi rst version was originally released in 2002 and will
be referred to as the "Standard" compressor in this Service Data sheet.
The Standard compressor was offered on Caterpillar ACERT Medium
and Heavy duty engines, and the DDC S60 EGR (2002-06) engine.
These installations required an externally-mounted inlet check valve
(ICV) on the air inlet side of the compressor. Depending on whether the
air induction system was naturally aspirated or turbocharged dictated
whether or not additional hardware was required along with the ICV
(See Figure 6, page 3 and Section 1 of "Air Induction", on page 6).
The second version was originally released in 2007 and will be referred
to as the "Closed Room" compressor in this service data sheet.
This compressor is only permitted to be naturally aspirated – use of
engine turbocharger as an air source is not allowed. This compressor
eliminates the need for an externally mounted inlet check valve (ICV)
on the air inlet side of the compressor (See Figure 6, page 3).
Refer to Figure 2 below to see the visual differences between the
two BA-921
compressor heads. Other differences between the two
versions will be referenced throughout this Service Data sheet.
The function of the air compressor is to provide and maintain
air under pressure to operate devices in air brake systems.
The Bendix
reciprocating compressor with a rated displacement of
15.8 cubic feet per minute at 1250 RPM.
The compressor consists of a water-cooled cylinder
head assembly and an integral air-cooled crankcase
The cylinder head assembly is made up of the cylinder
head, cooling plate and valve plate assembly and uses
Cylinder Head
With 4
compressor is a single-cylinder
Cast Iron
Cylinder Head
With 4
Valve Plate
two sealing gaskets. Depending on the application, the
cylinder head and cooling plate may be aluminum or cast
iron. The cylinder head contains air and water ports as
well as an unloader assembly. A cooling plate is located
between the cylinder head and valve plate assemblies and
assists in cooling.
The valve plate assembly consists of brazed steel plates
which have valve openings and passages for air and
engine coolant to fl ow into and out of the cylinder head.
Closed Room:
Cylinder Head
With 6


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   Summary of Contents for BENDIX BA-921 COMPRESSOR-STD-CLOSED ROOM

  • Page 1

    Valve Head ® ® This service data sheet covers two versions of the Bendix BA-921 compressor. The fi rst version was originally released in 2002 and will be referred to as the “Standard” compressor in this Service Data sheet. Valve Plate...

  • Page 2

    BA-921 ® compressors are equipped with a model, customer piece number, Bendix piece number and safety valve to protect the compressor head in the event serial number. See Figures 1 and 4. of, for example, a discharge line blockage downstream OPERATION of the compressor.

  • Page 3

    Discharge Air Inlet Standard Compressors use an Inlet Check Valve Valve Port (ICV), or alternately, an ICV plus a reservoir, Unloader Closed Discharge in the air inlet line depending on the application Port Port Air Dryer Governor Unloader Port Cooling Plate Governor Valve...

  • Page 4

    Air From Air From Air Inlet Port Governor Governor Unloader Unloader Port Port Cooling Plate Closed Unloader Valve Room Piston Up & Plate Unseated Unloader Piston Up & Unseated Air in Pistons Shuttles Back and Forth from the Air in Pistons Shuttles Back and Forth from the Piston to the Cylinder Head and Inlet Port During Piston to the Closed Room Unloaded Mode...

  • Page 5

    18 of this manual for AIR IN specifi c requirements. Compressed AIR OUT Coolant IN or OUT Governor Control ® ® FIGURE 11 - CLOSED ROOM BENDIX BA-921 COMPRESSOR CYLINDER HEAD...

  • Page 6

    Valve ENGINE) C11/C13/C15/C18 COMPRESSOR AIR INDUCTION SYSTEM (TURBOCHARGED) AIR INDUCTION Section 1: For Standard Compressors. GENERAL The Standard Bendix ® BA-921 ® air compressor can be used both with air induction systems that are naturally aspirated (atmospheric air) and pressurized (turbocharged). The following section covers Caterpillar and Detroit Diesel engine air induction arrangements.

  • Page 7

    Section 2: For Closed Room Compressors. 6. If an expansion tank is present (turbocharged air Bendix Closed Room BA-921 ® air compressors are induction systems only), inspect for any cracks and only permitted to be naturally aspirated –...

  • Page 8

    Bendix ® PuraGuard ® system can be use in have a vent cap (e.g. Bendix part number 222797) installed conjunction with a Bendix ® air dryer. in the port. Under no circumstances should the port be If compressor oil passing is suspected, refer to the plugged or left open.

  • Page 9

    1 Head Cap Screws (4) 2 Unloader Cover Cap Screws (2) (include washers) 3 Unloader Cover Splash Shield See Figure 10 6 Unloader Balance Piston 4 Unloader Cover for Port Details. 7 O-Ring 5 Unloader Cover Gasket 8 Spring 9 O-Ring 12 ST-4 ™...

  • Page 10

    1 Head Cap Screws (6) (include washers) 12 ST-4 ™ Safety Valve 2 Unloader Cover Cap Screws (2) 4 Unloader Cover See Figure 11 for 5 Unloader Cover Gasket Port Details. 6 Unloader Balance Piston 7 O-Ring 13 Cylinder Head 8 Spring 9 O-Ring 10 Unloader Piston...

  • Page 11

    Bendix “Test and Checklist” published in the Air Brake System Handbook (BW5057) and on the back of the Dual Circuit Brake System Troubleshooting Card (BW1396).

  • Page 12

    INJURY OR DEATH: within tolerance replace the compressor or repair the When working on or around a vehicle, the following general compressor unloader system using a genuine Bendix precautions should be observed at all times: maintenance kit available from authorized Bendix parts outlets.

  • Page 13

    unless specifi cally stated and approved by the PREPARATION FOR DISASSEMBLY vehicle and component manufacturer. Remove the balance of road dirt and grease from the 10. Prior to returning the vehicle to service, make exterior of the compressor with a cleaning solvent. If a rear certain all components and systems are restored end cover or end cover adapter is used on the compressor to their proper operating condition.

  • Page 14

    Section 2: Closed Room Compressor (refer to Figure 16) Side View 1. Remove the discharge safety valve (12) from the cylinder head (13). Compressor 2. To restrain the spring force exerted by balance piston Oil Supply spring (8) of the unloader assembly, hold the unloader Port cover (4) in place while removing the two unloader Engine...

  • Page 15

    plate assembly. They must be open and clear in both REAR END COVER (If Present) assemblies. Make certain not to damage the head. Check for cracks and external damage. Check the 3. Remove rust and scale from the cooling cavities and crankshaft rear bearing diameter in the rear end cover passages in the cylinder head, cooling plate and valve (25) for excessive wear, fl...

  • Page 16

    a. Position the gasket (27) on either the crankcase or assembly will match the outline of the cooling plate and the special crankcase cover and install the special valve plate assembly. crankcase cover on the crankcase using the four Note: To assist with correct installation, the alignment cap screws.

  • Page 17

    4. Install the cooling plate onto valve plate assembly by engine installations, an additional o-ring is required to lining up the alignment bushings on the cooling plate seal the oil feed passageway between the compressor over the oversized countersunk holes of the valve plate and engine gear case cover.

  • Page 18

    BA-921 ® COMPRESSOR SPECIFICATIONS (ALL) TORQUE SPECIFICATIONS: Standard Compressor Typical weight: Assembly Torques in inch pounds (in. Ibs.) Standard Compressor (DDC Model) ....... 66 lbs. M8x1.25-6g Cylinder Head.....265-292 In. Lbs. (30-33 N•m) Closed Room Compressor (DDC Model) ......55 lbs. M5x0.75-6g Unloader Cap ....

  • Page 19

    Appendix A Advanced Troubleshooting Guide for Air Brake Compressors The guide consists of an introduction to air brake charging system components, a table showing recommended vehicle maintenance schedules, and a troubleshooting symptom and remedy section with tests to diagnose most charging system problems. INDEX Symptom Page Number...

  • Page 20

    (less than 25%) duty cycle, operating in builds the air pressure for the air brake system. The air a temperate climate. See Bendix and/or other air dryer compressor is typically cooled by the engine coolant system manufacturer guidelines as needed.

  • Page 21

    Discharge line upgrades are not covered under warranty. Note: To help prevent discharge line freeze-ups, shorter discharge line For Bendix ® Tu-Flo ® 550 and 750 compressors, unloader service is lengths or insulation may be required in cold climates. (See Bendix recommended every 250,000 miles.

  • Page 22

    Discontinue using this test. Not a valid test. Results Do not use this card test to diagnose compressor "oil passing" issues. They are subjective and error prone. Use only the Bendix ® System Inspection Cup (BASIC ™ ) test and the methods described in this guide for advanced troubleshooting.

  • Page 23

    Return the vehicle to service. An optional kit (Bendix piece number 5011327 for the Bendix AD-IS or AD-IP ™ ® ® ™ air dryers, or 5003838 for the Bendix AD-9 ® air dryer) is available to redirect the air dryer exhaust.

  • Page 24

    BASIC test member.) in Table A on page A-3, some oil in cup (Bendix Air System Inspection Cup). If the reservoirs is normal. less than one unit of reservoir contents is found, the vehicle can be returned to ser- vice. Note: If more than one oil unit of...

  • Page 25

    45 degree fi tting. For more information on Kinked discharge line shown. how to help prevent discharge line freeze- ups, see Bendix Bulletins TCH-08-21 and TCH-08-22 (Appendix B). Shorter discharge line lengths or insulation may be required in cold climates.

  • Page 26

    Note: After all other operating conditions have been investigated. replacing a compressor, residual oil may Bendix compressors are designed to have a 'dry' take a considerable period of time to be sump and the presence of excess oil in the crankcase fl...

  • Page 27

    Symptom: What it may indicate: What you should do: 6.0 Excessive oil A problem with engine or other engine See engine service manual. accessory. consumption in engine. The engine service manual has more information. 7.0 Oil present Air brake charging system is functioning Air dryers remove water and oil from at air dryer normally.

  • Page 28

    These can increase the rate at which carbon Bendix Bulletins TCH-08-21 and TCH-08-22 builds up in the discharge line. Bendix recommends oil (Appendix B). Shorter discharge line soot (solids) be maintained at less than 3%.

  • Page 29

    Replace air dryer heater. exhaust port frozen open. (d) Compressor malfunction. Replace the compressor only after making certain the preceding conditions do not exist. * Note: For the Bendix ® DuraFlo ™ 596 air compressor, not only the governor, but also the SV-1 ™...

  • Page 30

    Symptom: What it may indicate: What you should do: 12.0 Air dryer (a) Restriction between air dryer and Inspect delivery lines to reservoir for reservoir. safety valve restrictions and repair as needed. releases air. (b) Air dryer safety valve Verify relief pressure is at vehicle or malfunction.

  • Page 31

    Symptom: What it may indicate: What you should do: (a) Compressor leaks air at connections 16.0 Compressor Check for leaking, damaged or defective leaks air or ports. compressor fi ttings, gaskets, etc. Repair or replace as necessary. (b) Compressor unloader mechanism Go to Test 6 on page A-15.

  • Page 32

    Tests Test 1: Excessive Oil Leakage at the Head Gasket Exterior leaks at the head gasket are not a sign that oil is being passed into the air charging system. Oil weepage at the head gasket does not prevent Look the compressor from building air.

  • Page 33

    Test 6: Compressor Unloader Leakage ® shut-off and charge the unloader port by allowing Bendix Compressors: Park vehicle, chock wheels, and follow all standard safety procedures. air pressure to enter the hose and unload the compressor.

  • Page 34

    30 days*** returning. (Note that 30-90 days is the recommended air tank known? drain schedule for vehicles equipped with a Bendix air dryer that YES, number of days is properly maintained.) If, in cold weather conditions, the 30 day was known (30 - 90 days) Replace the Compressor.

  • Page 35

    Footnote 2: To get an accurate reading for the amount of oil collected during a 30 day period, ask the customer not to drain the air tanks before returning. (Note that 30-90 days is the recommended air tank drain schedule for vehicles equipped with a Bendix air dryer that are properly maintained.) If, in cold weather conditions, the 30 day air tank drain schedule is longer than the customer's usual draining interval, the customer must determine, based on its experience with the vehicle, whether to participate now, or wait for warmer weather.

  • Page 36

    ™ Appendix B continued: Information about the BASIC Test Kit (Bendix P/N 5013711) ® Filling in the Checklist for the Bendix Air System Inspection Cup (BASIC ™ ) Test Note: Follow all standard safety precautions. For vehicles using a desiccant air dryer.

  • Page 37

    Last 3 feet, including fi tting at the end of the discharge line, must be insulated with ½ inch thick closed cell polyethylene pipe insulation. If the discharge line length must be less than 6 feet or greater than 16 feet, contact your local Bendix representative. A-19...

  • Page 38

    Other Requirements 10-16 ft. ½ in. None If the discharge line length must be less than 10 feet or greater than 16 feet, contact your local Bendix representative. System Leakage Check the air brake system for excessive air leakage using the Bendix “Dual System Air Brake Test and Check List”...

  • Page 39

    Appendix D Technical Bulletin Bulletin No.: TCH-008-022 Effective Date: 1/1/1994 Page: 1 of 1 Additional Cold Weather Operation Tips for the Air Brake System Subject: Last year we published Bulletin PRO-08-21 which provided some guidelines for “winterizing” a vehicle air brake system. Here are some additional suggestions for making cold weather vehicle operation just a little more bearable.

  • Page 40

    BW2369 © 2007 Bendix Commercial Vehicle Systems LLC. All Rights Reserved. 10/07. Printed in U.S.A.

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