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Some interesting facts and data about Cummins Big Cam engines.

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Cummins BigCam setting valves and PTD Injectors

 
Cummins NTC 855 Big Cam engine OBC (Outer Base Circle) common settings 

Torque Injectors
8.0 Nm, 72 inch.lb

Set Inlet valves, cold
0.36 mm, 0.014 inch

Set Exhaust valves, cold
0.69 mm, 0.027 inch


OBC (Outer Base Circle) Method for setting valves and injectors when standard PTD injectors are fitted.
  OBC Method:

1. Loosen all valves and injectors so that the engine turns freely while keeping the push rods in place.
2. Rotate engine clockwise until the "A, OR 1-6 VS" timing mark on the accessory drive pulley is aligned with the timing indicator on the front gear case, as shown in the illustration.
3. Set the injector and valves on cylinder #1 or #6 as required.
4. Mark the rockers of the valves and injector you have just set with a white pen to keep tabs on what you've done.
5. Rotate the engine to the next timing mark and set the appropriate valves and injector.
6. Proceed until all valves and injectors are set.
7. Two engine revolutions are required to set all the valves and injectors.

END of OBC Method:


Setting Cummins NTC 855 Big Cam top-stop injectors

 
Cummins N855 Top Stop Injectors common settings (IBC, Inner Base Circle Method) 

Torque Injectors
* 0.7 Nm, 6.0 inch.lb

Inlet valves, cold
0.28 mm, 0.011 inch

Exhaust valves, cold
0.58 mm, 0.023 inch


Use the IBC (inner base circle) method to set N855 engines when top-stop injectors are fitted.

The setting order and setting values for the valves and injectors is different from the OBC method described above, but you still use the same marks on the accessory drive pulley and the gear case for orientation.

IBC Method:

1. Loosen all valves and injectors so that the engine turns freely while keeping the push rods in place.
2. Rotate engine clockwise until the "A, OR 1-6 VS" timing mark on the accessory drive pulley is aligned with the timing indicator on the front gear case, as shown in the illustration.
3. Set the injector and valves on cylinder # according to the table below.
3. Mark the rockers of the valves and injector you have just set with a white pen to keep tabs on what you've done.
4. Rotate the engine to the next timing mark and set the appropriate valves and injector.
5. Proceed until all valves and injectors are set.
6. Two engine revolutions are required to set all the valves and injectors.

Table for setting top-stop injectors

 
With Timing Mark on A

When Valves on #5 are closed
Set Valves #5
Set Injector #3

When Valves on #2 are closed
Set Valves #2
Set Injector #4

With Timing Mark on B

When Valves on #3 are closed
Set Valves #3
Set Injector #6

When Valves on #4 are closed
Set Valves #4
Set Injector #1

With Timing Mark on C

When Valves on #6 are closed
Set Valves #6
Set Injector #2

When Valves on #1 are closed
Set Valves #1
Set Injector #5

* N.B. If you don't have a torque wrench

Note: The very low injector torque requires a special torque wrench. Do not exceed that torque.
You should be able to just rotate the pin, rocker to injector, with your fingers after torquing the injector.
0.7 Nm torque is very low torque, only about a quarter screw turn (90 degrees) more than finger tight.

END of IBC Method:



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