A 2008 Citroen 2.0L HDi had been fitted with a new Synchronous Belt Drive System (SBDS) kit. A few thousand miles later, the SBDS failed prematurely. The mechanic reported valve-to-piston contact and confirmed that the engine was extensively damaged. An element of mystery was provided by the fact that the drive belt from the Auxiliary Belt Drive System (ABDS) was no longer present.
A wide number of associated installation issues are known to contribute to the premature failure of an SBDS. These include incorrect tensioner set up; insufficient torque on the tensioner bolts; and subsequent failure of a water pump that was not installed at the same time as the timing belt kit.
Good workshop practices can be used to manage many of these issues however.
Appropriate installation procedures seemed to have been followed and a timing belt kit was fitted.
A diagnosis is impossible without a comprehensive examination of the vehicle. Once the Gates inspector (pictured, above) arrived, an immediate attempt was made to establish the sequence of events that led to the failure of the SBDS.
Two things were immediately apparent:
1) The ABDS belt was missing completely
2) The water pump had not been changed
Let’s consider the second point first.
Although it was clear that this water pump hadn’t contributed to the engine damage and had remained fully operational, the inspector recommended water pump replacement at the scheduled change as it had completed the same duty cycle as the belt.
An undetected leak will lead to drive system failure so it is sensible to install a new water pump at the same time as the kit. This achieves a complete drive system overhaul and preserves drive system integrity. Moreover, if the water pump is sourced from the same supplier as the belt kit, a single investigation will be required in the event of any subsequent problems.
The missing ABDS belt drew attention to other factors that may contribute to premature drive system failure. These include misalignment and foreign substances (oil, water, debris) in the drive.
The garage confirmed that although a visual check of the ABDS was made at the time of the original job, none of the ABDS parts were replaced. The ABDS was examined and scoring was evident on the SBDS drive cover. This suggested belt chafing and this may have been a factor causing the belt to break.
Debris in the main drive system would compromise the timing belt. So what if the debris included fragments from the missing ABDS belt? The SBDS cover was removed and the sequence of events became clear. Fragments of the ABDS belt were wrapped around the crankshaft pulley. This had wound down into the drive, causing the pulley to fail and making valve-to-piston contact inevitable.
Although garages may be confident that good workshop practices have been observed, failure to replace the water pump at the same time as the belt kit undermines their case.
Although the water pump was not culpable in this case, strong evidence links them with premature SBDS failure, therefore Gates recommends replacement in every case.