Bendix Air Compressor Assembly


All torques specified in this manual are assembly torques and can be expected to fall off after assembly is accomplished. Do not retorque after initial assembly torques fall.

To convert pound inches of torque to pound feet of torque, divide inch pounds by 12.

pound inches ÷ 12 = pound feet.

To convert pound feet of torque to pound inch of torque, multiply pound feet by 12.

pound feet × 12 = pound inches

Cylinder Head Assembly

1. If the discharge valve stop was removed and must be replaced, a sealant such as “LOCKTITE RETAINING COMPOUND #75”, must be applied to the stop and its corresponding bore in the cylinder head. Before applying the sealant, make certain that the press fit between the discharge valve stop outside diameter and the valve stop bore in the cylinder head is a minimum of 0.033 mm (.0013 in) and a maximum of 0.071 mm (.0028 in). If this fit cannot be maintained, a new cylinder head body must be used. Be sure to completely support the outside top of the cylinder head casting, while pressing in the replacement stops.

IMPORTANT: The cylinder head must be supported in a fashion that allows the machined head surface to be parallel to the arbor press bed and perpendicular to the press ram. This is necessary to permit the discharge valve stop to be installed squarely in its bore and to minimize the possibility of “cocking”.

2. Install the discharge valve spring, discharge valve and valve seat. Using a 9/16 inch hex wrench, torque the discharge valve seat to 52 to 66 N·m (70 to 90 lb ft).

3. Test for leakage by the discharge valve. Apply 700 kPa (100 psi) of air pressure through the cylinder head discharge port and apply a soap solution to the discharge valve and seat. A slight 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 valve off its seat several times. This will help the valve 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 exposed on the top of the cylinder head casting. No leakage is permitted.

4. If the unloader piston bushing was removed, press in a new bushing following the same pressing procedures given in Step 1. The inside diameter of the unloader piston bushing must be between 19.042 mm (.7497 in) and 18.948 mm (.7460 in) after pressing.

5. Using a 3/8 hex wrench, install the unloader piston stop and O-ring in the head. Torque to 20 to 25 N·m (175 to 225 lb in).

6. Install the unloader piston and O-ring in the head so that the short stem of the piston rests on the unloader stop.

7. Install the unloader piston spring, small end first, on the stem of the unloader piston. Install the metal (copper) inlet valve gasket so that it rests on the shoulder of the inlet valve cavity. Install the inlet valve seat on top of the inlet valve gasket with its beveled side visible. Make certain the large coils of the piston spring rest within the recess of the inlet valve seat on the side opposite the bevel. Install the inlet valve so that it rests on the beveled side of the valve seat.

8. Install the inlet valve spring on the inlet valve stop and install the stop in the head. Using a spanner wrench, torque the inlet valve stop to between 52 to 66 N·m (70 to 90 lb ft).

9. Apply 700 kPa (100 psi) air pressure to the unloader port of the governor mounting pad and note the inlet valve is driven away from its seat. Using a soap solution, test for air leakage at the unloader piston stop. No leakage is permitted.

Crankcase & Crankshaft Assembly

1. If the compressor requires a drive end crankshaft oil seal, press it into the crankcase until it is flush with the crankcase casting. Using clean oil lubricate the sealing lips of the seal.

2. If the compressor uses a ball type main bearing, press the ball bearing onto the correct end of the crankshaft. Position the ball bearing and the crankshaft in the crankcase, making sure the drive end of the crankshaft is positioned in the crankcase as marked before disassembly.

NOTE: In the case of compressors with a rear main ball bearing, make certain to install the thrust bearing in the crankcase before pressing the crankshaft and ball bearing into place. Carefully press the crankshaft and ball bearing into the crankcase using an arbor press. Make certain not to damage the oil seal, if the compressor is so equipped.

3. Place the O-ring seal in the groove around the rear end cover or in the crankcase proper in the event a rear main ball bearing is in use. If the rear end cover contains a precision sleeve bearing that serves as the crankshaft main bearing, make certain to install the thrust bearing. Install the end cover in the position as marked before disassembly, taking care not to damage the sleeve bearing, if so equipped.

4. Install the four cap screws or nuts that secure the rear end cover to the crankcase and torque to 20 to 25 N·m (175 to 225 lb in).

Piston & Connecting Rod Assembly

1. Prelubricate the piston, piston rings, wrist pin connecting rod.

2. Install the piston rings in the correct location the ring pipmarks up (Refer to Fig. 10). Stagger the position of the ring gaps.

3. Align the wrist pin bore of the connecting rod with the piston bores and install the wrist pin to secure the rod to the piston. Make certain the TEFLON “buttons” are installed in each end of the wrist pin.

4. Using an automotive type ring compressor or similar tool, compress the piston rings and gently install the connecting rod and piston in the cylinder bore. Install the connecting rod cap on the connecting rod in the same position as marked during disassembly.

5. Secure the rod cap to the rod using the two cap screws and special lockwashers. Torque the cap screw to between 14 to 16 N·m (120 to 140 lb in) and bend the tabs of the lockwashers until they are firmly against the flats of the hex head of the cap screws.

Base Plate Or Base Adapter Assembly

1. Position the base plate or base adapter gasket on the crankcase and install the base plate or base adapter as marked before disassembly.

2. Install the cap screws that secure either the crankcase base plate or crankcase mounting base adapter. Torque the cap screws evenly to the appropriate valve: base plate 10 to 13 N·m (85 to 115 lb in), mounting base adapter 20 to 25 N·m (175 to 225 lb in).

Final Compressor Assembly

1. Place the cylinder head gasket on the crankcase and position the head on the crankcase as marked during disassembly. A gasket sealer is neither required or recommended.

2. Secure the cylinder head to the crankcase using the four cylinder head cap screws. Torque the cap screws in an “X” pattern to between 20 to 25 N·m (175 to 225 lb in).

3. Using a thread sealant install all necessary pipe plugs and torque as follows:

1/8 inch P.T. plugs 10 to 12 N·m (85 to 105 lb in).

1/2 inch P.T. plugs 23 to 31 N·m (200 to 270 lb in).

4. Install all crankshaft keys making certain to support the crankshaft to avoid bearing damage. Install the crankshaft nut where applicable. When installing drive couplings, gears or pulleys, DO NOT EXCEED 165 N·m (120 lb ft) torque on the crankshaft nut. The self locking crankshaft nut used on the BX-2150 requires that it be installed so that the narrow castellation slots are toward the end of the crankshaft and not against the pulley, coupling or gear that the nut retains.

Some BX-2150 through drive compressors require the installation of a spline coupling on the rear of the crankshaft. The cap screw securing the coupling should be torqued to 20 to 25 N·m (175 to 225 lb in).

5. Use covers, plugs, or masking tape to protect all ports if compressor is not to be installed immediately. Protect the ends of the crankshaft against damage by wrapping with masking tape or friction tape. The open bottom of a vertical engine lubricated compressors should be protected against the entrance of dirt during handling or storage, by installing a temporary cover over the base.

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