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Changing Belts on the Cummins ISB

This is a description of how I changed the two belts on my 1997 Discovery with the 275 ISB Cummins engine. Just a reminder that each engine and each coach may be different. So please go easy, and check your situation against what I say here. I have left my references to belt sizes and bolt sizes because they are probably different than mine anyway.

On my engine, changing the belts is relatively easy if you have the correct tools and parts. First on my engine I have two belts. One drives the air conditioner and the other drives the alternator, water pump, and fan. The first belt is a simple "V" belt using a simple tensioning idler pulley adjustment. The other belt is a serpentine "V Ribbed" flat belt tensioned by a spring loaded belt tensioner and idler pulley.

All work was performed from the top of the engine under the bed. So the first thing to do is remove all the "things" that have accumulated under the bed and raise the engine cover(s).

Removal of Air Conditioner Belt:
To remove the air conditioner belt I first loosened the bolt that holds the tensioning idler and allow the idler to swing down and release the tension on the belt. If replacing this belt, remove it by slipping it over each of the fan blades (if you haven't cleaned the engine and radiators you will wish you had at this step in the game!). This may take time as the belt is JUST long enough to slip over the individual fan blades with no slack to spare. Now is a good time to check the idler pulley bearing for wear, looseness and or lack of lubrication. Grab the pulley and rotate rocking from side to side to check for wear. Mine was bad and I had an alternator repair shop put a new bearing in the pulley. Check the air conditioner pulley also.

Removal of Alternator/Water Pump/Fan Belt:
First take notice, and if possible take pictures, of the belts routing. This is where a neat little trick helps get the belt off. On the back of the spring loaded tensioner, you will feel a square hole that is exactly 3/8 of an inch square. It fits a 3/8 inch square drive socket ratchet. I used a ? inch breaker bar with a ? to 3/8 inch square drive adapter. By placing the breaker bar into the hole you can pull the tensioner back against the spring tension and put slack into the belt. On my breaker bar there is a hole drilled through the handle end. This allowed me to tie a rope from the bar end to part of the engine so the tentioner will remain swung up and out of the way. I used a hole in the air conditioner mounting bracket for the other end of the rope. Now you can remove the belt by slipping the belt off the idler pulleys, alternator and engine flywheel. Now slip the old belt over the fan blades to completely remove. Check the two idler pulley bearings for wear and or looseness.

Install the new belt over the fan blades and route the ribbed side of the belt on the engine flywheel, water pump/fan pulley, alternator pulley and the smooth side over the two idler pulleys. Now you can slowly release the spring loaded tensioner. Check the belt for correct placement on the ribbed pulleys and verify that all the ribs are seated correctly.

Install the air conditioner belt over the fan blades and onto the pulleys. Tension is applied by pulling the tensioner up and locking it into place with the bolt.

Submitted by - PETER SHAFFER
97 36RS 275 ISB


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