GM 1.7 Turbo Diesel Timing System


Problems in the market persist with the failure of the belt tensioner on the 1.7-litre turbo diesel engine used in many Vauxhall/Opel and Isuzu vehicles following the prescribed belt and tensioner change specified by the vehicle’s official service schedule.

The issue is further complicated as there are at least ten versions of this unit, each with its own design variant. However, the cause of the most common failure occurs because the belt is over tensioned, which because of its design is very easy for the technician installing the belt to do. However, being forearmed with the knowledge that this is a possibility, it is equally easy to avoid if the correct fitting procedure is followed.

It is essential that workshops undertaking this repair understand that the failure is rarely a product quality issue, so a warranty claim for this problem will almost certainly be rejected. In the overwhelming majority of cases, the cause of the failure is as a direct result of the incorrect installation of the new belt and tensioner, so workshops must ensure that the technicians tasked with the repair follow all of the technical guidelines. If these procedures are followed, a failure of this nature is extremely unlikely.

The reason that the belt can become over tight is because although it is straightforward to install the new spring loaded tensioner, it is also very easy for it to move while it is being secured and just a small movement can make a big difference on the tension on the belt.

To demonstrate the extent of this phenomenon, if during its tightening the tensioner moves by only four or five degrees, the tension on the belt will increase threefold from the 20kg it is designed for to a catastrophic 60kg plus. This then causes the tensioner to wear excessively and ultimately, distort and fail.

To prevent this costly problem, Dayco recommend technicians follow its published fitting procedure designated for the specific engine code and make sure that they tighten the bolt to the manufacturers specified tension, which is also stated by engine code in the Dayco technical sheet.

This is particularly important as it seems more than a coincidence that the most common failures tend to occur on the Z17DTH and Z17DTL units, which both feature tensioners that have a lower torque setting than the majority of the other engine codes.

Fitting Procedure

Naturally the precise detail of the fitting procedures differ according to the engine code, but to set an accurate tension of the belt, the engine must be cold and so it should have been at rest for at least four hours, and common to all of models are the following:

1)      The TDC locking bolts must be installed in the camshaft sprocket and the high-pressure pump sprocket. The lug on the crankshaft pulley must be in line with the lug on the oil pump cover.

2)      Observe the direction of engine rotation, the timing belt must be installed and tensioned in the direction of the arrows in a clockwise direction starting from the crankshaft, oil pump, fuel pump, camshaft and tensioner pulley.

3)      Not all engine codes need this step, but Z17DTH and Z17DTL units require the TDC bolts to be removed and the crankshaft rotated 60° in the direction of engine rotation.

4)      Tighten the tensioner bolt to the vehicle manufacturers specified torque for the engine code in question, making sure the tensioner does not move during this operation. It is advised to make a reference point to make sure the tensioner has not moved.

5)      Dependent upon the engine code, the crankshaft must be rotated between two and six revolutions in the direction of engine rotation to the adjustment position

6)      The lug on the crankshaft must then be in line with the lug on the oil pump cover.

7)      Reinstall the TDC bolts to the camshaft and fuel pump sprockets, if it is not possible to install these freely then the tension procedure must be repeated.

To simplify the process further, technicians can use a Dayco Tensiometer, which will ensure the correct tension is achieved. The tool is easy to use and just needs the relevant test code for the belt application to be entered and the belt vibrated. If the test reading is ‘OK’ the belt is fine, but if the result reads + or – three, the belt will need to be reset.

Product Quality

Depending on the variant, Dayco provides either timing belt kit KTB414 or KTB468 for the GM 1.7 turbo diesel engine, but both options contain a High Tenacity (HT) or ‘white’ belt.

The Dayco HT belt has become the original equipment (OE) solution for an increasing number of vehicle manufacturers. As a result, more vehicles fitted with these white belts are coming into the workshop and it is only Dayco that can provide the aftermarket with a truly matching OE product, because only Dayco HT kits replicate the vehicle manufacturers OE installation.

In addition to the obvious benefit that this quality gives the independent sector, the kit also provides them with the potential to improve upon the standard two-year warranty.

Dayco’s unique Long Life + 1 year warranty is free of charge to the factor, workshop and motorist, but extends the warranty on the Dayco HT belt from the existing two years, to a market leading three-year term, which is great news for workshops choosing Dayco.

For more information regarding the OEM quality power transmission products in the Dayco range, please email: or visit:


For further information relating to this press material, please contact Steve Coombes on: 01753 650004 or e-mail:

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