- Side Abrasion - This is a prime indicator of pulley misalignment and typically is a sign of a failing tensioner. With the engine off, test the tensioner for a worn-out pivot bushing which allows the pulley arm to swing out of parallel with the belt.
“Modern ABDSystems can tolerate 1 degree of misalignment, after which excess heat will begin to accumulate. This excess heat builds at a rate of 30 degrees F for each additional 1 degree of arc in misalignment, and heat build-up can damage other components, particularly bearings.
“Misalignment must be located and corrected before installing a replacement belt, to avoid damaging the new belt.
- Pilling - Small, shiny spots or streaks of rubber material appear deep in the belt valleys when pilling has occurred. “Excess heat - often due to belt slip - has melted small amounts of rubber, which are deposited in the belt valleys where they re-harden. This excess material causes the belt to ride on top of the pulley ribs (rib topping).” Significant loss of traction, additional belt slip and increased heat and noise can result.
“Remember, a worn belt will still turn the accessories and appear to be working even if it can’t transfer the power effectively, say Gates officials.
TIGHTEN THINGS UP
The condition of the serpentine belt is one of two important factors that determine the efficiency of the ABDSystem, Gates says. The other is the proper function and adjustment of the tensioner.
Technicians should consider tensioners a “wear part,” too, and inspect and replace them on a similar schedule as belts. Gates recommends a one-to-one replacement ratio between EPDM serpentine belts and automatic tensioners.
“Since much of the labor required for an ABDSystem repair is the same whether or not the tensioner is replaced, the relatively small cost of the part itself provides cost-effective insurance for long life and top performance of the ABDSystem.”
The tensioner performs two important jobs for the ABDSystem, officials say. First is to provide the correct belt tension for optimum transmission of power from the crankshaft to the accessory components, throughout its duty cycle. The second function is to absorb and dampen impulses and shocks introduced by cylinder firing, high acceleration/deceleration and accessory on/off cycles.
DIAGNOSING TENSIONER ISSUES
Gates officials say there are three distinct sets of symptoms that indicate tensioner failure and help diagnose the nature of the failure. “It’s always a good rule to observe the system in operation before removing or replacing any belt. This will allow you to observe two particular areas of concern while the engine is in operation: belt tracking and tensioner operation.”
The symptom sets are:
- Excessive belt noise or squealing - These symptoms indicate belt slip, which can be caused by loss of spring tension in the tensioner. This can be due to a broken spring, or one that has simply become weak from age.
“Replacement of both the belt and the tensioner is recommended to break the cycle of worn components causing premature wear to new components.”
- Pivot bushing wear - It’s not uncommon for a tensioner to cycle a billion times within a 100,000-mile period. A new tensioner has a precise, tight fit between the pivot arm and the tensioner body. As the pivot bushing wears out through repeated tensioning cycles, it allows the arm to swing out of parallel, causing the belt to “off track” which may create side abrasion or rib damage.
“This damage can be as little as slight scrubbing on one side of the belt, to as much as a significant tear or rib chunk-out. In cases of extreme wear, or outright failure of the bushing, the belt can jump pulley ribs, or come off entirely, stranding the vehicle.”
- Damper failure - The damper is a device inside the tensioner body that acts like a brake shoe, slowing down the pivot arm’s return from absorbing system shocks and cylinder-fire pulses. Some “budget” tensioners do not have a damper. When the damper fails, the tensioner arm will oscillate, resulting in increased loads on the pulley and shaft bearings and/or seals of adjacent accessories.
In worst cases, the tensioner and belt will “hammer” adjacent accessories resulting in premature failure of those components as well.
Technical Editor Dave Cappert takes a look at timing-belt service, as well as some of the specialty tools required by some OEMs for the service.