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 Tech Tips - NT/N14 OBC Overhead Set Procedure
Tech Tips - Setting OBC STC Injectors

There has been much confusion about setting STC injectors, particularly those CPL's that have reverted to setting injectors using the OBC (Outer Base Circle) method.  The information contained here applies only to those engines with STC injectors that are set using the OBC method.

This information was compiled from information provided by Cummins Engine Co. and is believed to be reliable.  Please consult your service manuals for additional details.


Rotate the accessory drive in the direction of engine rotation.  The accessory drive will rotate clockwise, when looking at the front of the engine.  Align the "A" or "1-6 VS" mark on the accessory drive pulley with the pointer on the gear cover.

Note:  It is important to adjust the injector first before adjusting the valves on a cylinder when using the OBC overhead set procedure.

Check the valve rocker levers on cylinder #1 to see if both valves are closed.  Both the intake and exhaust valves are closed when both rocker levers are loose.  If both valves are not closed, then rotate the accessory drive a complete revolution and align the "A" or "1-6 VS" mark again.  If the valve rocker lever adjusting screws have been loosened and not yet adjusted, watch the valve push tubes as the engine rolls towards the mark.  Both valve push tubes will have moved to the downward (or valve closed) position if the engine is on the correct stroke.

Outer Base Circle (OBC) Injector and Valve Adjustment Sequence

Bar Engine in
Direction of Rotation

Pulley
 Position

Set Cylinder

Injector

Valve

Start
Advance to
Advance to
Advance to
Advance to
Advance to

A
B
C
A
B
C

1
5
3
6
2
4

1
5
3
6
2
4

Firing Order: 1 - 5 - 3 - 6 - 2 - 4


Refer to the engine model and CPL for the correct injector rocker lever adjusting screw torque value.

Engine Model CPL Injector Screw Torque Intake Valve Lash Exhaust Valve Lash C-Brake Lash
NBCIV 821, 833, 903, 904, 806 105 in lbs 0.014" 0.027" 0.018"
88BCIV 910, 827, 1185, 1188, 1210, 1211, 1256, 1280 90 in lbs 0.014" 0.027" 0.018"
N14 1374, 1380, 1395, 1405, 1507 125 in lbs 0.014" 0.027" 0.023"


Use a dial type torque wrench to tighten the injector lever adjusting screws to the specified torque.  If the screw causes chattering during setting, repair the screw and lever as required.  Hold the torque wrench in a position that allows you to look in a direct line at the dial to insure that you are reading it accurately.  The torque wrench must be calibrated and have a range of 150 in. lbs.

On non-brake engines, if the injector screw is a slotted type.  Be careful that the screw driver does not slip out of the slot.  These screws can be (and should be) replaced with the hexagon type.

Hold the adjusting screw and torque the lock nut to 40 ft lbs on a New Big Cam IV and 88 Big Cam IV's and to 50 ft lbs on N14 models.

After setting the injector on a given cylinder, set the valves on the same cylinder.  Notice that the OBC method requires new valve settings for the New Big Cam IV and the 88 Big Cam IV engines.  Hold the adjusting screw and torque the locknut to 54 ft lbs on New Big Cam IV and 88 Big Cam IV's and to 50 ft lbs on N14 models.

Advance the accessory drive pulley to the next mark and adjust the injector and valves.  Continue through two revolutions of the engine to complete all six cylinders.
 

C-Brake Set Position - Sequence

Bar in Direction

Pulley
Position

Set Brake

IBC

OBC

Start
Advance to
Advance to
Advance to
Advance to
Advance to

A or 1-6VS
B or 2-5VS
C or 3-4VS
A or 1-6VS
B or 2-5VS
C or 3-4VS

5
3
6
2
4
1

1
5
3
6
2
4

Firing Order: 1 - 5 - 3 - 6 - 2 - 4  Right Hand Rotation

In setting the C-Brake, the OBC or IBC sequence can be used.  However, to eliminate confusion, it will be easier to use the same sequence that was used to set the overhead.

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