The premature failure of an accessory belt drive system in a 2001 Peugeot 306 1.8D 8V (engine code XUD7) provides another mechanical mystery for the Gates inspector to solve.
The driver of the Peugeot 306 had complained about a rattling noise. On inspection, the garage traced it back to the Accessory Belt Drive System (ABDS). It was clear to the installer that a worn Torsional Vibration Damper (TVD) was the root cause of the problem. The TVD was replaced with a Gates part. A Gates accessory belt was fitted at the same time.
TVDs help to protect the crankshaft from fatigue. They contain rubber damping membranes that help reduce the vibrations that can cause damage. As a result, TVDs play a key role in stabilising the overall performance of the ABDS. It is because their role is to reduce vibrations that TVDs themselves become subject to wear.
Within two weeks of the original repair, the Peugeot 306 was brought back into the workshop on a recovery vehicle for rectification. It had apparently suffered premature ABDS failure.
A new inspection was completed and the problem seemed crystal clear. The mechanic and the workshop foreman at the scene concluded that the new TVD had failed. Catastrophic engine failure had occurred. It seemed likely that debris from the TVD and/or the accessory belt had contaminated the Synchronous Belt Drive System (SBDS), compromised the smooth running of the main drive system and caused the drive to fail. After reporting the issue to the motor factor, a claim was registered. The Gates inspector was asked to investigate.
From the debris inside the SBDS, the Gates inspector isolated some remains of the rubber membrane from inside the TVD. This rubber membrane had indeed caused the SBDS issue. Once it had penetrated the SBDS cover, premature failure was inevitable. This had caused the seizure and subsequent engine damage. After a full inspection of the ABDS was carried out, another potential cause of the Peugeot 306’s problems emerged.
Wherever there are multiple components in the ABDS, Overrunning Alternator Pulleys (OAPs) are frequently employed. OAPs are used in systems to resolve issues caused by increased alternator loads. As opposed to traditional solid pulleys, they allow the alternator to ‘free-wheel’ or ‘overrun’ every time the engine decelerates.
At the same time, the OAP dampens vibrations at the alternator. This protects the alternator and means less wear on the belt, as well as less wear on the other components in the drive system. A worn OAP exposes other components to more vibrations and accelerates wear. Like TVDs, their role in reducing vibrations makes them subject to wear.
On inspection, the OAP was found to have seized. A seized OAP would compromise the smooth running of the belt, and this raised a series of additional drive system problems.
Symptoms and causes
Perhaps by replacing the original TVD, the installer had merely cured a symptom, rather than resolved the actual cause of the problem. It’s possible that the seized OAP was the cause of the initial rattling problems reported by the customer. Alternatively, the OAP might have seized after the new TVD was installed. In that case, it would have caused the newly installed TVD to fail prematurely, so it could have been the cause of the subsequent engine failure.
The experience highlights the difficulties when attempting to diagnose problems within the ABDS. Replacement of an individual component in an ABDS that exhibits wear is not good workshop practice. When the OE drive was assembled, all the components were new. By the time the belt is due for replacement, all bearings on all components will have completed the same duty cycle.
Once a component has suffered wear, the other components in the system are exposed to additional vibrations. For example, damaged overrunning alternator pulleys can neither dampen vibrations effectively, nor transmit power to the alternator properly. This compromises the other accessories in the drive system, leading to excessive tensioner movement and the risk of further problems, for example. It is also important to replace the overrunning alternator pulley when a new alternator is installed.
Moreover, a single, new component, changes the dynamics of the drive. Replacing all the other components as part of a drive system overhaul is always good practice.