Toothed belt drives camshaft, high pressure fuel pump (injection pump), oil pump, and brake booster vacuum pump.
The drive of the gas distribution mechanism, as well as the injection pump for diesel engines, require very precise settings. After changing the tension of the belt or after replacing it, it is necessary to carry out its adjustment, which in turn requires knowledge, experience and time. Therefore, when performing service maintenance, the main work related to the toothed belt is limited to checking its condition and tension.
When adjusting the toothed belt tension or when removing it (e.g. for replacing or dismantling the cylinder head) it is necessary to adjust the valve timing and the start of the injection pump supply. This can only be done by a specialist and, in addition, special tools and devices are needed.
The tools necessary for adjusting the valve timing can be ordered from a specialized workshop, however, it is quite difficult to make a control and measuring device with an arrow indication and a corresponding adapter for setting the start of injection pump supply. Therefore, it is recommended that these settings be made in the workshop.
1. Turn out the screw of an expanding clamp on an end face of a protective casing of a toothed belt.
2. Press out the two fastening latches and remove the upper part of the protective cover (see arrows in illustration). The lower part of the protective cover can only be removed after dismantling the crankshaft belt pulley by unscrewing the two mounting bolts.
Status check
3. Make sure the timing belt is free from oil and cracks. The teeth of the belt must be intact with no signs of wear.
4. Rotate the engine to check the condition of the belt along its entire length. A defective belt must be replaced with a new one.
Tension check
Checking the tension of the toothed belt is carried out together with checking its condition. To check the toothed belt tension on TD engines, a special tester VW 210 is required. This tool allows you to measure the tension of a toothed belt of a certain length.
TD engine
5. Press your hand on the toothed belt in the section between the gears of the camshaft and the injection pump shaft so that the belt deflection is at the measurement point.
6. Install the control and measuring device at the place of deflection on the mentioned segment and record the reading of the device (see illustration).
7. Rotate the crankshaft once.
Attention! Rotate the crankshaft only with the belt pulley on the crankshaft or the alternator pulley. Do not rotate the crankshaft using the camshaft pulley!
8. Repeat the toothed belt tension measurement and record the value. If the device shows a value of 12-13, then the tension is normal. Otherwise, adjust the belt tension.
TDI engine
The TDI engine has a tensioner pulley with automatic adjustment of the toothed belt tension. The tension check is performed as follows:
9. Install the tension roller so that the notch (excavation) and the shoulder on it stood opposite each other. In this position of these marks, the toothed belt tension is correct (see illustration).
10. Check up work of the mechanism of a tension roller. To do this, press the toothed belt with your hand. The notch and shoulder on the tension roller should move relative to each other.
11. Release the belt. The notch and shoulder of the tension roller should again be opposite each other. If this is not the case, correct the tension of the toothed belt or replace the tension roller.
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