Drivers and mechanics of heavy duty vehicles understand that front-end accessory drive components such as serpentine belts and belt tensioners, although durable, will eventually wear and require replacement to maintain proper performance. This procedure involves a 2007 Volvo VNL series truck equipped with a Cummins ISX 15-liter engine that has over 931,000 miles and is due for maintenance.
Before starting any work on the engine, necessary safety precautions must be taken including setting the parking brake, removing the keys from the ignition, and disconnecting the vehicle’s battery.
Signs of Belt and Tensioner Wear
There are multiple ways to inspect a tensioner while the engine is running. Noise from the tensioner may indicate the need for inspection with the engine off. If the serpentine belt tracks improperly or is off-center, it signals bushing wear causing tension or alignment loss. Other signs include loss of tension, sticking, or notching movement.
Testing belt noise with the engine running can help diagnose issues. Lightly spraying the rib side of the belt with water will increase noise if the cause is low belt tension. If the noise temporarily disappears and returns as the belt dries, the noise is chirping caused by misalignment, which is the most common cause of belt noise.
Removing and Inspecting Belts
Tools Required
Use a ½ inch ratchet (long handle preferred) to relieve tension on the belts and remove serpentine belts from the pulleys.
With both the fan belt and alternator AC belt removed from the pulleys, slide the serpentine belts out of the engine compartment. Inspect the belts using the Deco wear gauge, which checks rib profile, rib depth, and cracking.
EPDM belts lose rubber similarly to tires, which can be checked by the rib depth bar on the gauge. Side to side rib movement checked by the gauge crown indicates the belt should be replaced if the gauge moves. Avoid using belt dressing on EPDM belts as it contaminates and damages the rubber. Also look for cracks, missing chunks, abrasion, and pilling signs especially on older neoprene style belts.
The choice of a high-quality Cummins engine belt is essential for durability and proper operation, especially in heavy duty applications.
Inspecting and Replacing the Tensioner
Remove the fan and alternator tensioners using a 13mm socket. Inspect the removed tensioner for bearing noise and metal-to-metal contact between the arm and spring case, which indicates bushing wear. Replace the tensioner if cracks or breaks are found in the arms or spring case.
Checking Pulley Alignment
With the belts and tensioners removed, check for misalignment in the belt drive system using the Eiko laser alignment tool included in the Deco belt diagnostic kit. Connect the laser and receiver to different pulleys. If the laser shines through the word “Deco” on the receiver, the pulleys are properly aligned.
Installing New Tensioners and Belts
The fan tensioner should be replaced with a Deco 89440 gold label tensioner, which features a flat spring and heavy cast casing designed to withstand the demands of rugged diesel engines. Both the fan and AC serpentine belts must be replaced using Deco gold label belts. These belts are engineered with EPDM rubber compounds to resist heat and harsh underhood conditions.
Preparation of Mounting Surfaces
Before installing the new tensioners, clean the engine’s mounting surfaces with light abrasive sandpaper or abrasive pads. Excessive oxidation or debris can cause uneven mounting surfaces and lead to misalignment, which is the primary cause of belt noise.
Mounting and Torque Specifications
Locate the pin holes on the bracket and position the tensioner into the mounting holes. Tighten the bolts with a 13mm socket until snug. Deco recommends using a torque wrench to tighten bolts to 35 foot-pounds.
Final Installation and Testing
Finish the installation by fitting the serpentine belts and releasing the tensioners to apply pressure to the belts. Reconnect the battery and start the engine. It is critical to verify that all belts are properly aligned within the pulley groups. A belt installed even one groove off can operate temporarily but will lead to premature failure. Run the engine for a few minutes to allow the belt to sync properly.
| Step | Key Actions |
|---|---|
| Safety First | Set parking brake, remove keys, disconnect battery |
| Inspection Signs | Noise, off-center belt, tension loss, notching, misalignment |
| Belt Removal | Use ½ inch ratchet, remove fan and alternator belts |
| Belt Inspection | Use Deco gauge to check rib profile, depth, cracking |
| Tensioner Inspection | Check for bearing noise, metal contact, cracks |
| Alignment Check | Use laser alignment tool to verify pulley alignment |
| Installation | Clean surfaces, mount tensioner, torque bolts to 35 ft-lbs |
| Final Test | Install belts, release tensioner, verify alignment, run engine |