NT/N14 STC Outer Base Circle (OBC) Overhead Set Procedure

Need help setting STC injectors, specifically setting injectors using the OBC (Outer Base Circle) method? There has been some confusion with engines that have STC injectors that are set using the OBC method, so let us help you!


Rotate the accessory drive ih the direction of engine rotation. The accessory drive will rotate clockwise, on a right hand engine, 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 No.1 to see if both valves are closed.

NOTE: Both the intake and exhaust valves are closed when both rocker levers are loose and can be moved from side to
side. If both valves are not closed, rotate the accessory drive one complete revolution; and align the” A” mark with the
pointer again.

If the valve rocker lever adjusting screws have been loosened and not yet adjusted, watch the valve push tubes
as the engine rolls upon the “A” mark. Both valve push tubes will have moved to the downward (valve closed)
position if the engine is on the correct stroke.

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


Use a dial type torque wrench to tighten the injector rocker 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. This is to make sure that
you read the dial accurately.

The torque wrench must be calibrated, have a resolution of 0.28 Nm [2.5 in-Ib], and have a range of 17 Nm [150
in-Ib].

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


Hold the adjusting screw and torque the lock nut to 54 Nm [40 It-Ib] on New Big Cam IV and 88 Big Cam IV’s
and 68 Nm [50 It-Ib] on N14 models.

Alter setting the injector’ on a given cylinder, set the valves on the same cylinder. Notice that the OBC method requires new valve settings for New Big Cam IV and 88 Big Cam IV engines. Hold the adjusting screw and torque
the lock nut to 54 Nm [40 It-Ib] on New Big Cam IV and 88 Big Cam IV’s and 68 Nm [50 It-Ib] on N14 models.

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


In setting the C-Brake, the OBC or IBC sequence can be used.


However, to eliminate confusion, it will be easier to user the same sequence that was used to set the overhead.

Jimmy Finch

Dallas Branch Manager, M&D Distributors

Jimmy Finch has over 33 years of experience in Diesel Engine Sales, Service and Repair. His experience started early in life at Texas Fuel Injection Service (an early acquisition of M&D) as a job with a means to an end. Somewhere in that 33 years this job turned into a fulfilling career. He started in the injector clean up department and has held practically every position leading up to his current role as Branch Manager of the Dallas, Texas location.

In his spare time, Jimmy enjoys spending time with his wife of 24 years, Priscilla. They are currently getting ready to make their way into the empty-nesters stage of life. He also enjoys the occasional hunting trip with friends and family and chasing down potential customers by the names off their trucks.

No Comment.

By posting a comment, you acknowledge and agree to M&D's terms and conditions.

Diesel Engine Parts

for Your Diesel Engine's Needs