Series 50 – Section 29.2 Cylinder Compression Test

Section 29.2
Cylinder Compression Test

The following tool is to be used when performing the cylinder compression test, J 6692-B . See Figure "Cylinder Compression Test Tool" .‪

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Figure 1. Cylinder Compression Test Tool

  1. Run engine until normal operating temperature is reached and shut down the engine.
  2. Clean and remove the rocker cover. Refer to "1.6.2 Cleaning and Removing of Two-piece Rocker Cover-Diesel Engines Only" .

    Note: If cover is two-piece design, it is not necessary to remove bottom.


    All the fuel must be removed from the cylinder head before removing an injector to prevent the fuel from entering the cylinder and causing hydrostatic lock or wash down.‪

  3. Remove the inlet and outlet lines from the fuel fittings at the rear of the cylinder head. Blow low compressed air into the inlet fitting for 20 to 30 seconds or until all of the fuel is purged from the cylinder head.
  4. Remove the two rocker shaft through bolts and one nut from the front rocker shaft assembly and lift the rocker shaft assembly off the engine. Refer to "1.3.2 Removal of Rocker Arm Assembly" .


    Turning the screws too far will damage the threads in the injector solenoid housing.‪

  5. Loosen the injector wire terminal screws two (2) full turns and remove the terminal wires. Do not remove the screws from the injector. The wire terminals have keyhole slots to fit over the screw head.
  6. Remove the injector hold down crabs.


    Extreme care should be used when handling the injectors to avoid costly damage by dropping or otherwise mishandling. When replacing the injectors, always replace the injector O-rings.‪

  7. Remove the three injectors from the cylinder head. Refer to "2.3.2 Removal of Unit Injector" .
  8. Place three compression test adaptors J 38768 into the injectors holes. See Figure "Test Adaptor " .
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    Figure 2. Test Adaptor

  9. Install the injector hold down crabs and torque the hold down bolts to 58-66 N·m (43-49 lb·ft). See Figure "Injector Hold Down Crabs" .
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    Figure 3. Injector Hold Down Crabs

  10. Remove the rocker arm assemblies from rocker arm shaft. Refer to "1.3.2 Removal of Rocker Arm Assembly" .
  11. Remove the three injector rockers and replace with oil control sleeves J 38768-5 part of J 38768 .
  12. Install rocker arm assemblies with sleeves and in place back on rocker arm shaft.
  13. Install rocker arm shaft assembly on head. If engine is equipped with Jake Brake, you must use non-Jake Brake rocker arm bolts. Torque the two bolts and the nut to 102-109 N·m (75-80 lb·ft). Refer to "1.3.4 Installation of Rocker Arm Shaft Assembly" .
  14. Prime the fuel system. Refer to "13.5.3 Fuel Lines and Flexible Hoses" .
  15. Disconnect the gray connector (injector drive) from the ECM for the A-bank injectors.

    Note: To avoid excessive oil splash, place the bottom half of a two-piece design rocker cover, with head to cover gasket installed, on the cylinder head. Install a few bolts and tighten.

  16. Start engine and run until coolant out temperature reaches 38°C (100°F).
  17. Attach cylinder compression gauge J 6692-B to first adaptor. See Figure "Cylinder Leakage Tester" .

    Note: Cylinder compression gauge J 6692-A part of J 6692-B can be upgraded to J 6692-B by ordering J 6692-18 part of J 6692-B .

    Click to see this graphic in a separate window

    Figure 4. Cylinder Leakage Tester

  18. Push pressure relief valve at gauge several times until highest compression reading is reached. Series 50 engine specification is 3103-3792 kPa (450-550 lb/in2 ) with no two cylinders differing by more than 276 kPa (40 lb/in.2 ).

    Note: If compression readings are below specifications listed in Table "Compression Pressures at Various Altitudes" , you will need to repeat step 17 several times to be certain.

  19. To determine proper cylinder compression, compare the test results to those listed in Table "Compression Pressures at Various Altitudes" .

    Altitude, ft

    Atmospheric Pressure/lb/in.2 (kPa)

    12 L Compression Pressure ± 50 /lb/in.2 (345 kPa)

    11.1 L Compression Pressure ± 50 /lb/in.2 (345 kPa)


    14.7 (101)‪

    539 (3716)‪

    587 (4047)‪


    14.17 (98)‪

    519 (3579)‪

    566 (3903)‪


    13.66 (94)‪

    501 (3304)‪

    545 (3758)‪


    13.17 (91)‪

    483 (3330)‪

    526 (3627)‪


    12.69 (88)‪

    465 (3206)‪

    507 (3496)‪


    12.22 (84)‪

    448 (3089)‪

    488 (3365)‪


    11.77 (81)‪

    431 (2972)‪

    470 (3241)‪


    11.34 (78)‪

    416 (2868)‪

    453 (3123)‪


    10.9 (75)‪

    399 (2751)‪

    435 (2300)‪


    10.5 (72)‪

    385 (2655)‪

    419 (2889)‪


    10.1 (70)‪

    370 (2551)‪

    403 (2779)‪

    Table 4. Compression Pressures at Various Altitudes
  20. Disconnect the gray connector (injector drive) from the ECM for the B-bank injectors in step 15 Then repeat steps 2 through step 17 for the three rear cylinders.

Series 50 Service Manual - 6SE50
Generated on 10-13-2008

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