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The Garrett (formerly Airesearch) GT 35 turbocharger is used on all Series 50G engines. See Figure 35356 . ‪

1. Wastegate Actuator ‪

5. Compressor Housing ‪

2. Turbine Housing ‪

6. Braided Line to Intake Manifold ‪

3. Water-Cooled Center Housing Rotating Assembly (CHRA) ‪

7. Compressor Recirculation Valve ‪

4. Bolted Joints ‪

8. Actuator Hose ‪

GT 35 Turbocharger Assembly (Coach)

The turbocharger is designed to increase the overall power and efficiency of the engine. Power to drive the turbocharger is extracted from the energy in the engine exhaust gas. ‪

The CHRA consists of a turbine wheel and shaft, a compressor wheel, and a center housing that serves to support the rotating assembly, bearings, seals, a turbine housing, and a compressor housing. The center housing has connections for oil inlet, oil outlet, water inlet and water outlet fittings. ‪

The rotating assembly consists of a turbine wheel and shaft assembly, piston ring(s), thrust spacer, compressor wheel, and wheel retaining nut. The rotating assembly is supported on two pressure-lubricated bearings that are retained in the center housing by snap rings. Internal oil passages are drilled in the center housing to provide lubrication to the turbine wheel shaft bearings, thrust washer, thrust collar, and thrust spacer. Internal water passages provide cooling and subsequent protection against oil cooking in the housing. ‪

The turbine housing is a heat-resistant alloy casting that encloses the turbine wheel and provides a flanged engine exhaust gas inlet and an axially located turbocharger exhaust gas outlet. The turbine housing is secured to the turbine end of the center housing. An internal turbine bypass valve, commonly called a wastegate, allows exhaust gas to flow around the turbine wheel. This provides control over the maximum boost pressure. ‪

The wastegate is controlled with a pneumatic actuator mounted on the side of the turbine housing. The Series 50G coach engine turbocharger has an actuator with a single hose port on the top side of the actuator can with a silicon hose that runs to a port on the compressor cover. The Series 50G Genset engine turbocharger is equipped with threaded ports on both the top and bottom sides of the can. Braided steel lines connect to these ports; the top port line is run to a port on the compressor outlet, while the bottom port line is run to the fuel mixer housing. See Figure 27371 for Genset configuration. Air pressure from the compressor outlet is fed through the line to the top side of the actuator, which opens the wastegate valve at a specified pressure. To prevent natural gas from leaking into the atmosphere, the bottom port on the Genset actuator serves only as a safety return to the mixer housing, in case of an actuator diaphragm failure. ‪

1. Wastegate Actuator ‪

6. Bypass Port Cover ‪

2. Turbine Housing ‪

7. Braided Line to Compressor Housing ‪

3. Water-Cooled Center Housing Rotating Assembly (CHRA) ‪

8. #4 Threaded Top Port ‪

4. Bolted Joints ‪

9. Braided Line to Fuel Mixer Housing ‪

5. Compressor Housing ‪

10. #3 Threaded Bottom Port ‪

GT 35 Turbocharger Assembly (Genset)

The turbocharger is mounted on the exhaust outlet flange of the engine exhaust manifold. After the engine is started, the exhaust gases flow from the engine and through the turbine housing causing the turbine wheel and shaft to rotate. See Figure 27365 . ‪

Schematic Air Flow Diagram (Series 50G)

The gases are discharged into the exhaust system after passing through the turbine housing. On automotive engines, an oxygen sensor and exhaust temperature sensor are installed within 12 inches of the turbocharger turbine outlet. A harness connects the sensors to the ECM. ‪

The compressor wheel, in the compressor housing, is mounted on the opposite end of the turbine wheel shaft and rotates with the turbine wheel. The compressor wheel draws in clean air, compresses it, and delivers high pressure air through the intake manifold to the engine cylinders. The compressor housing (on the coach version only) also contains a bypass valve, referred to as a compressor recirculation valve. This valve relieves compressor boost during a rapid deceleration of the engine. The Genset turbo does not have a valve installed; a cover plate seals these passages on the compressor housing. See Figure 27371 . ‪

Oil for lubricating the turbocharger is supplied under pressure through an external oil line extending from the oil filter adaptor to the top of the center housing. Water for cooling the bearing housing is supplied from the oil cooler, and is returned to the top of the thermostat housing. See Figure 27368 . ‪

1. Elbow, Oil Drain Tube ‪

9. Connector, Oil Supply Tube (from oil filter adaptor) ‪

2. Tube, Turbo Oil Drain ‪

10. Tube Assembly, Turbo Oil Supply ‪

3. Bolt, and Lockwashers, Oil Drain Tube Mounting ‪

11. Bolt, Oil Supply Tube Clip ‪

4. Gasket, Oil Drain Tube ‪

12. Clip, Oil Supply Tube ‪

5. Elbow ‪

13. Gasket, Turbo Exhaust Inlet ‪

6. Clamp ‪

14. Water Supply Line ‪

7. Nut, and Washer Turbo Mounting ‪

15. Water Return Line ‪

8. Turbocharger Assembly ‪

Turbocharger Oil/Water Lines Series 50 Gas

From the oil inlet in the center housing, the oil flows through the drilled oil passages in the housing to the shaft bearings, thrust ring, thrust bearing, and backplate or thrust plate. See Figure 27366 . ‪

1. Compressor Wheel ‪

6. Shaft ‪

2. Thrust Bearing ‪

7. Turbine Wheel ‪

3. Backplate ‪

8. Shaft Bearings ‪

4. Oil Inlet ‪

9. Oil Outlet ‪

5. Center Housing ‪

10. Water passages ‪

Turbocharger Oil Flow Diagram (Series 50G)

The oil returns by gravity to the engine oil pan through an external oil line extending from the bottom of the turbocharger center housing to the cylinder block. Water flows through the bearing housing in a U-shape flow path, removing heat generated by the hot exhaust gas in the turbine. ‪

Repair or Replacement of Turbocharger (Series 50 Gas)

To determine if repair is possible or replacement of the turbocharger is necessary perform the following procedure. See Figure 21458 . ‪

Flowchart for Repair or Replacement of Turbocharger (Series 50 Gas)

Cleaning and Removal of Turbocharger (Series 50G)

Cleaning the turbocharger is not necessary before removal. ‪


To avoid injury from hot surfaces, wear protective gloves, or allow engine to cool before removing any component.

Prior to removal, visually check for: ‪

  1. Missing or loose nuts and bolts.
  2. Loose or damaged intake and exhaust ducting.
  3. Damaged oil supply and drain lines.
  4. Cracked or deteriorating turbocharger housings.
  5. External oil leakage.
  6. Damaged water supply and return lines.
  7. Damaged recirculation valve line.
  8. Replace damaged parts with new parts.

To remove the turbocharger, perform the following: ‪


Do not attempt to remove carbon or dirt buildup on the compressor or turbine wheels without removing the turbocharger from the engine. If chunks of carbon are left on the blades, an unbalanced condition will exist and subsequent failure of the bearings will result if the turbocharger is operated. However, it is not necessary to disassemble the turbocharger to remove dirt or dust buildup. ‪

  1. Disconnect and remove the CAC ducting at the compressor housing.
  2. Disconnect and remove the air inlet hose attached to the compressor housing.
  3. Disconnect the exhaust outlet pipe from the turbine housing of the turbocharger. For proper operation, the turbocharger rotating assembly must turn freely. Whenever the exhaust ducting is removed, spin the turbine wheel by hand.
  4. Remove the inlet oil line from the top of the center housing.
  5. Remove the oil drain line from the bottom of the center housing.


    Be sure to drain coolant before removing water lines from bearing housing. ‪

  6. Remove water lines from bearing housing.
  7. Remove recirc valve line (Coach only).
  8. Remove actuator return line on bottom port of actuator.
  9. Attach a chain hoist and a suitable lifting sling to the turbocharger assembly.
  10. Remove the nuts securing the turbocharger assembly to the exhaust manifold. Then, lift the turbocharger assembly away from the engine and place it on a bench.
  11. Cover the end of the oil drain line, the oil outlet line, water supply, water return, the air inlet and the exhaust outlet openings on the engine and turbocharger to prevent the entry of foreign material.


    To avoid injury from improper use of chemicals, follow the chemical manufacturer's usage, handling, and disposal instructions. Observe all manufacturer's cautions.

  12. Clean the exterior of the turbocharger with a non-caustic cleaning solvent before disassembly.

Disassembly of Turbochargers (50G)

Disassemble the turbocharger as follows: ‪

  1. Mark the related positions of the compressor housing, center housing and turbine house with a punch or scribe to assure reassembly in the same relative position.


    Exercise care when removing the compressor housing and turbine housing to prevent damage to the compressor and turbine wheels. ‪

  2. Loosen and remove the bolts and retaining clamps securing the compressor housing to the backplate assembly and remove the compressor housing.
  3. Loosen and remove the bolts securing the turbine housing to the center housing. See Figure 27367 .

    1. Compressor Housing ‪

    5. Center Housing Rotating Assembly (CHRA) ‪

    2. O-ring ‪

    6. Turbine housing ‪

    3. Retaining clamp (compressor housing) ‪

    7. Bolt (turbine housing) ‪

    4. Bolt (compressor housing) ‪

    Series GT 35 Turbocharger (50G)

  4. Remove the turbine housing from the center housing.
Inspection and Cleaning of Turbocharger (Series 50G)

Damage can result from a contaminated exhaust system. Any debris left in the exhaust system after service work can fall back into the exhaust wheel. If large enough, these particles may cause turbine wheel damage at initial engine startup. The exhaust manifold and exhaust piping attached to the turbocharger should also be inspected for debris and cleaned, if necessary, before being installed. ‪

Any time the charge air cooler is removed, all charge air cooling system components must be inspected to make sure they are clean and free of any casting slag, core sand, welding slag, or any other contaminants that could break free during engine operation and damage the turbine wheel. ‪

Inspect the disassembled turbocharger, discarding any damaged parts, in the following manner: ‪

  1. Visually check for nicked, crossed or stripped threads.
  2. Visually check the turbine wheel shroud and turbine wheel for signs of rubbing.
  3. Visually check the compressor wheel for signs of rubbing or damage from foreign material. The wheel must be free of dirt and other foreign material.
  4. Check actuator can for external damage.
  5. Check actuator pressure setting; refer to Section .
  6. Check compressor cover recirculation valve (coach only).
  7. Visually check wastegate lever arm, valves, and ports. Make sure the ports are completely covered by the valves.
  8. Check the bearing axial end play:
    1. Clamp the center housing assembly in a bench vise equipped with soft jaws. See Figure 20423 .
    2. Fasten the dial indicator and magnetic clamp, part of magnetic base dial indicator set, J 7872-2 part if J 7872 , to the center housing so that the indicator tip rests on the end of the rotating shaft on the compressor side. See Figure 20423 .
    3. Checking Bearing Axial End Play

    4. Move the shaft axially back and forth by hand. The total indicator reading (thrust float) should be 0.0127-0.0889 mm (0.0005-0.0035 in.). If the total dial indicator readings do not fall within the specified limits, replace the rotating assembly.
  9. Check the shaft radial movement as follows:

    Due to the internal construction of the GT 35 bearing housing, access to the shaft through the oil drain is not possible. Therefore, radial movement cannot be accurately measured to determine the condition of radial turbine bearings. ‪

    To determine the general condition of the radial bearings, check radial end play after the turbocharger is cleaned and assembled. Push on the end of the shaft, towards the side of the compressor (or turbine) housing. If the wheel contacts either housing, the radial bearings may be worn out, and the CHRA should be replaced (be sure to check if the housing is seated and installed correctly also). ‪

  10. Service of the center housing rotating assembly (CHRA)

    The CHRA is serviced by replacement only. Do not attempt disassembly of the CHRA, as possible shaft imbalance and damage may result. ‪

Compressor Recirculation Valve for Coach Engine

Garrett Turbochargers for the Series 50G coach engine are equipped with an integrally mounted compressor recirculation valve. See Figure 27282 . The Series 50G genset engines do not have this feature; a cover plate is installed over the compressor housing. ‪

1. Gasket ‪

5. Diaphragm support ‪

2. Diaphragm and piston assembly ‪

6. Screw ‪

3. Cover ‪

7. Compressor housing ‪

4. Spring ‪

Compressor Recirculation Valve for the Series 50G Engine

The recirculation valve is designed to prevent or significantly reduce engine air system pressure pulsation and turbocharger surging during engine throttling operations. ‪

The recirculation valve consists of a spring-loaded diaphragm and piston assembly contained between a diaphragm support and a cover. Three screws are used to mount the cover, which is sealed by a gasket, to the compressor housing. ‪

The recirculation valve is a self-contained unit and requires no adjustments or lubrication during normal operation. ‪

The compressor recirculation valve permits some of the compressed charge air, which becomes trapped during engine throttling, to return back to the compressor intake system. This prevents or significantly reduces pressure pulsation otherwise experienced with compressor surging. ‪

During acceleration and steady state operation the recirculation valve remains in its normally closed position. In this mode, engine intake manifold pressure admitted to the top of the recirculation valve, and assisted by a spring, keeps the diaphragm and piston assembly pressed against the diaphragm support, sealing off the recirculation port in the compressor housing. ‪

The outside of the diaphragm is exposed to compressor boost pressure through the porting in the compressor housing and via the holes in the side of the diaphragm support. During engine throttling, while boost pressure is still available, but with intake manifold pressure dropping off sharply to a vacuum, the resulting pressure differential opens up the recirculating valve diaphragm and piston and permits the remaining compressed charge air to recirculate to the compressor intake system. ‪

The recirculation valve is a small aluminum dome-like structure attached with three Torx head M6 screws to the turbocharger compressor housing near the discharge. When servicing the recirculation valve, the following tools and equipment are required: ‪

  • A Service Kit, consisting of a diaphragm and piston assembly and a gasket.
  • A flat, clean work area.
  • A pair of pliers to loosen the hose clamp on top of the valve.
  • A T30-Torx driver for the three mounting screws.
  • A hand-held vacuum pump is essential, for checking the proper function of the service assembly.
  • Mark the orientation of the cover with respect to the compressor housing base, before removing the valve (helps during assembly).

Pre-Test Recirculation Valve for the Series 50G Engine

Inspect the recirculation valve as follows: ‪

  1. Attach a hand-held vacuum pump to the fitting on top of the valve and apply vacuum of 61-74 kPa (18-22 in. Hg.).
  2. If this vacuum decays to half of its value in less than 5 seconds, or if a vacuum cannot be established at all, the valve is not functioning properly and needs to be replaced.

Removal and Replacement of Recirculation Valve for the Series 50G Engine

Remove recirculation valve as follows: ‪

  1. Remove the braided line that connects to the fitting on the top of the recirculation valve cover.
  2. Remove the fitting from the valve cover.
  3. Using a T30-Torx driver, loosen the three screws at the base of the valve cover. To facilitate backing out the screws, press the cover down against the internal spring force. Remove and save all three screws.
  4. Slowly release the pressure and let the cover rise up from the base.
  5. Reach below the cover and hold the internal assembly at the plastic diaphragm support. Lift it off and turn it over.
  6. At this time, the gasket between the cover and the compressor housing can be removed and discarded.

    Note: Both surfaces must be clean and free of any gasket or other foreign particles before a new gasket will be installed during re-assembly.

  7. With the assembly upside down, lift off the diaphragm support and lay it aside.
  8. Lift off the diaphragm and piston assembly and discard it.
  9. Clean off any foreign particles from the cover and the spring.
  10. With the cover upside down, re-insert the spring, then drop the new diaphragm and piston assembly over the spring, followed by the previously laid-aside and cleaned diaphragm support.

    Note: That the diaphragm support squeezes the diaphragm against the upper shoulder in the cover after it is fully assembled and seated against the compressor housing base.

    Note: Lightly coat the base of the cover with a non-hardening grease, just enough to hold the NEW gasket in place when the assembly is turned over for installation.

  11. Position the new gasket so it lines up with the rim of the cover and the three holes.
  12. Hold the assembly loosely together and position it over the mounting base of the compressor housing.
  13. Check for proper orientation (a mark applied before disassembly will come in handy) and compress the assembly against the spring force 1.47-1.58 Nm (13-14 lb in) and install the three Torx screws. Continued pressure on the cover will facilitate the installation of the screws in an easy and even manner.
  14. After the cover has seated, torque the screws evenly to a value of 5.9-6.6 Nm (52-58 lb in).
  15. Re-install fitting in the valve cover. Use sealant.
  16. Re-attach braided steel line to fitting 8.13 Nm (6 lbft) of torque.

Checking Wastegate Calibration for the Series 50G Engine

This procedure provides a method for verifying proper wastegate calibration. ‪

  1. Remove hose from wastegate actuator (for gensets, remove line on top side of can).
  2. Set-up an indicator at the end of the wastegate actuator adjusting rod to measure actuator rod travel. The indicator should have a minimum travel of 0.100 in.
  3. Connect regulator and pressure gage set-up to wastegate actuator. See Figure 27284 .

    1. Hose to Wastegate Actuator ‪

    4. Supply Air Shutoff Valve ‪

    2. Vent Valve ‪

    5. Pressure Regulator ‪

    3. Pressure Gage ‪

    6. Shop Air Supply ‪

    Checking Wastegate Calibration for the Series 50G Engine

  4. Apply specified calibration pressure (listed in Table ) to the wastegate actuator.



    Set Pressure Travel at 0.04 Rod

    Coach ‪

    275 Hp ‪

    275 Hp ‪

    18.5 lb/in.2 (short can) ‪

    21.0 lb/in.2 (long can) ‪

    Genset ‪

    180 Kw, 60 Hz150 Kw, 60 Hz ‪

    31 lb/in.2 19 lb/in.2

    Series 50G Wastegate Calibration Pressure at 0.04 in. Rod Travel


    For genset turbochargers, NEVER apply pressure to bottom part of actuator can. Damage to actuator may result. ‪

  5. Close air supply shutoff valve. The pressure should hold at the specified pressure. If not, check air hose and fitting connections for leaks. If none are found, replace wastegate actuator assembly. Refer to Section .
  6. Open vent to relieve pressure. Check gage for zero pressure reading. Adjust regulator to zero pressure and close vent valve.
  7. Adjust dial indicator so it just contacts the actuator rod end and adjust to zero reading.
  8. Open air supply shutoff valve and slowly adjust regulator until dial indicator reads 0.040 in. Switch pressure on and off, opening and closing supply air and vent valves, to make certain dial indicator travel is from 0.00 in. to 0.040 in. and that the pressure reading is consistent.
  9. For currently calibrated wastegate actuator, a pressure within 0.25 lb/in.2 of the value listed in Table , will be required to obtain precisely 0.040 in. actuator travel. If the pressure required is outside this range, wastegate adjustment is necessary; refer to Section .

Removal and Replacement of Series 50G Wastegate Actuator

This procedure describes the removal of a actuator currently mounted on a turbocharger, and the replacement with a new service actuator. Further adjustment of the actuator will be necessary to achieve the correct pressure setting, listed in Table . ‪

  1. Remove actuator hose from the top side of the actuator can. With the pressure gage set-up (see Figure 27284 ), apply enough pressure to the actuator can until the rod begins to move; refer to Section .
  2. Remove the retaining clip that holds the actuator rod end on the wastegate lever pin. Lift rod off the wastegate lever pin.


    Never remove the rod end from the wastegate lever pin unless pressure is applied to the top side actuator port; otherwise, damage to the actuator diaphragm may result. ‪

  3. Remove the lock nuts that secure the actuator can to the base of the actuator bracket, and remove the can from the turbocharger assembly.

Replace wastegate actuator as follows: ‪

  1. Install actuator can on bracket; tighten lock nuts.
  2. Using pressure gage set-up, apply enough pressure to the new service actuator can until the rod begins to move.
  3. Adjust actuator rod end by turning either clockwise or counter-clockwise on rod so that the rod end hole lines up with the wastegate lever arm, while wastegate is held shut pin, slip rod over pin.
  4. Before installing the retaining clip again, the rod end will need to be adjusted to the correct setting. Refer to Section .

Setting the Wastegate on the Series 50G

This procedure describes the set pressure adjustment of an installed wastegate actuator. Before following this procedure, first check the actuator set pressure to see if adjustment is needed refer to Section . ‪

  1. Loosen the jam nut that secures the rod end on the actuator rod. If locking collar is present on the actuator rod, remove and discard collar, see Figure 27283 .

    1. Wastegate Actuator Assembly ‪

    4. Adjusting Rod End ‪

    2. Locking Collar ‪

    5. Retainer Clip ‪

    3. Jam Nut ‪

    6. Wastegate Lever and Pin Assembly ‪

    Wastegate Adjustment

  2. Remove the retaining clip that holds the actuator rod end on the wastegate lever arm pin.


    For genset actuator, never apply pressure to the bottom side of actuator port. Damage to the actuator may result. ‪

  3. Using pressure gage setup (see Figure 27283 ) apply enough pressure to the top side actuator can port until the rod begins to move, lifting the wastegate valve off of it's seal.
  4. Slip rod end off of wastegate lever arm pin.
  5. Adjust rod as needed
    • To INCREASE pressure setting at 0.04 in. turn rod end CLOCKWISE.
    • To DECREASE pressure setting at 0.04 in. turn rod end COUNTERCLOCKWISE.
  6. With pressure still applied to actuator, replace rod end on wastegate lever arm
  7. Check actuator set pressure again; refer to Section .
  8. If actuator is still out of adjustment, repeat this procedure again.
  9. If actuator is within specified set pressure, re-install retaining clip on wastegate lever arm pin.
  10. Tighten jam nut to secure rod end.

Assembly of Turbocharger Series 50G

Use the following procedure to assemble the turbocharger: ‪


As the parts are assembled, cover the openings to prevent entry of dirt or other foreign material, which may cause component damage. ‪

  1. Cover all openings.
  2. Position the Center Housing Rotating Assembly (CHRA) into the turbine housing as marked at disassembly, and line up bolt holes. Apply anti-seize compound to bolts, and torque to 185-215 lb/in.2 (1276-1482 kPa).


    Always remove the compressor cover before positioning on the Center Housing Rotating Assembly (CHRA); as damage to the O-ring can result. ‪

  3. Position the compressor housing as marked at disassembly against the CHRA and secure it in place with the bolts and clamps.
  4. Lightly lubricate the threads of the bolt with engine oil and torque the nut to 145-165 lb in. (16-19 Nm).

Installation of Turbocharger Series 50G

To install the turbocharger: ‪

  1. Attach a chain hoist and a suitable lifting sling to the turbocharger assembly.
  2. Remove any covers that were placed over the openings of the air inlet and exhaust outlet openings on the engine and turbocharger when the turbocharger was removed.
  3. Remove any covers on the oil inlet and drain lines, and the oil inlet and drain openings on the turbocharger.
  4. Place the turbocharger assembly into position on the exhaust manifold. Use a new gasket between the exhaust manifold and the turbine housing flange.
  5. Secure the turbocharger to the exhaust flange. Tighten the nuts just enough to hold the turbocharger in place.
  6. Slide the charge air cooler air inlet tube hose over the compressor housing outlet opening and secure it in place with the hose clamps.


    To avoid injury from flying debris, wear a face shield or goggles.


    Do not use any type of lubricant on the inside of any air inlet hose or on the hose contact surfaces of the turbocharger compressor housing, CAC ducting or the intake manifold. ‪

  7. Torque the turbocharger to exhaust manifold locknuts to 58-73 Nm (43-54 lbft).
  8. Install the oil drain line, using a new gasket, between the opening in the bottom side of the turbocharger center housing and the drain hose that runs to the cylinder block. Torque the bolts to 30-38 Nm (22-28 lbft).
  9. Refer to Section for verification of proper turbocharger installation.
  10. Install water supply and return lines.
  11. Install compressor recirculation line.