Cummins Idler Pulley Upgrade on NT32

By Robert Claycomb — Deneige, NT 32-276, Santa Barbara, California

I have a Cummins 6bta 5.9 engine. This might have been a Covid driven project, but I just changed out my Cummins Idler Pulley to the upgraded model as suggested by Seaboard Marine, Oxnard California (

The first step is to remove the engine front pulley/belt shroud. I also unscrewed the window washer fluid reservoir and moved it out of way.

To release the tension on the serpentine belt, I used a 1/2 inch breaker bar. Since I did not have another person available nor do I have a third arm and to keep fingers out of harms way, I used an 18 inch long piece of 3/4 inch PVC pipe as a support piece. I also screwed two pieces scrap metal pieces in the shape of a Vee to one end, which makes a cradle. (Afterwards, I felt that just the PVC pipe would in itself have been sufficient.) 

Next, put the breaker bars end into the square hole on the tensioner and lift up the bar. Then place the support piece beneath the breaker bars handle and then let the breaker bar handle back down and settle into onto the support. With the pressure off, the serpentine belt will then slide off. Next I unbolted and remove the old idler pulley. 

Per Seaboard, drill out the bracket using a 7/16 inch bit. Note: best to use a 90 degree drill motor to accomplish this. A friend loaned me his Dewalt 90 degree drill motor.  (Thank you David, NT 32-260.)

Drilling out the hole took a few minutes, as I stopped every so often to spray cutting fluid at the drill spot. Next, I taped the nut into the jaws of an open end of a long handled 17 mm wrench, (taped to keep the nut in place). I slipped the wrench into the very tight space and slowly turned the bolt until the threads caught. Once the threads were caught, the bolt was torqued to 55 ft pounds.

I put a new serpentine belt (green belt) on and removed the support brace and allowed the tensioner to do its thing. Note: Seaboard Marine has a Serpentine belt map. I fired up the Cummins and all was well. Lastly, I put the shroud back on and screwed the washer reservoir back to its spot.  

The job took about four hours and cost me $267.00 for the pulley and belt.

Photos of the Installation Process:

Pry the dust cover off the factory idler pulley. Put a 1/2 breaker bar end into the square hole on the tensioner. I made a support to keep tension off of the belt to make removal and later belt installation easier on me. 
I used a new standard length 7/16”stepped down to 3/8” bit with a 90 degree 3/8 drill motor.

Hole drilled. Afterwards (no photo) the area was cleaned up and repainted.
Not much room to put the nut on, I used a 17 mm wrench and taped the nut to the wrench end so as to not drop the nut.  The finished install photo.
Photo curtesy of Seaboard Marine showing the belt map.



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