3116 and 3126 HEUI Truck Engines Belts – Inspect

Inspect the belts when the engine is stopped.

Inspect the condition and the adjustment of the alternator belt and the accessory drive belt. Examine the belts for wear. Replace the belts if the belts show any signs of wear. Loose or worn pulley grooves cause belt slippage and low accessory drive speed. If belts are too loose, the belts vibrate enough to cause unnecessary wear on the belts and pulleys and possibly slip enough to cause overheating.

If belts are too tight, unnecessary stresses are placed upon the pulley bearings and on the belts which might shorten the service life of both.

If one belt in a set requires replacement, always install a new matched set of belts. Never replace just the worn belt. If only the worn belt is replaced, the new belt will carry all the load, as it will not be stretched as much as the older belts. All the belts will fail in rapid succession.


Belt tensioner.

* If the engine is equipped with a freon compressor (air conditioner), the belt for the fan drive, the alternator, and the accessories will have an automatic belt tensioner.
* If the engine is NOT equipped with a freon compressor, the alternator is used to adjust the belt tension.

Remove the belt guard. Inspect the condition and adjustment of alternator belts and accessory drive belts (if equipped).

To check the belt tension, apply 110 Newton (25 lb) of force, perpendicular to the belt, midway between the pulleys. Measure the belt deflection. Correctly adjusted belts will deflect 9 to 15 mm (3/8to 5/8 inch).

If the belt does not require replacement or adjustment, install the belt guard. If the belt requires adjustment or replacement, perform the following procedure to adjust the belt tension.

Alternator Belt Adjustment


(1) Adjusting bolt. (2) Mounting bolt.

1. Slightly loosen mounting bolts (2) and adjusting bolt (1).

2. Move the pulley to adjust the belt tension.

3. Tighten adjusting bolt (1). Tighten mounting bolts (2).

4. Install the belt guard.

If a new belt is installed, check the belt adjustment again after 30 minutes of engine operation at rated speed.

Water Pump Belt Adjustment


Exploded view of a water pump belt drive assembly: (1) Mounting bolt. (2) Square hole. (3) Adjusting bolt.

1. Slightly loosen mounting bolt (1) and adjusting bolt (3).

2. Adjust the belt tension with a square drive in the square hole (2).

3. Tighten adjusting bolt (3). Tighten mounting bolt (1).

4. Install the belt guard.

If a new belt is installed, check the belt adjustment again after 30 minutes of engine operation at rated speed.

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