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Tension pulleys for safe belt drive
The tension pulley is a belt drive component, maintaining the prescribed tension of the belt. A defective tension pulley results in a belt rupture. Depending on what type of belt is tensioned by the pulley, this could mean the end of the engine. Therefore the tension pulley is part of the replacement set in the most important belt drives.
Which belts does a car have?
Several car engine components are driven by a belt. These are:
- Servo pump
- possibly hydraulic pump for the brake booster
- injection pump
- water pump
Furthermore, the valve control of 75% of all new cars is driven by a belt. Belt drive is very cheap and maintenance-friendly. However, its belt must be kept at the correct tension at all times. When there is no other solution available, the tension pulley is the most suitable component to this end.
Function of a tension pulley
A tension pulley is built in such away, allowing it to build up pressure and tension on the belt drive. There are several ways to realise this. A very simple and reliable system is the non-central installation of the pulley on the engine block. If the drilling hole for its mounting bolt is not right in the middle of the tension pulley, this enables stepless alteration of its effective radius. This construction is found in many Volkswagen engines. Other tension pulleys move on a rail, establishing the required tension of the belt.
Purchasing the tension pulley separately
The tension pulley is part of the timing belt replacement set. Running a new timing belt with an old tension pulley is way too risky. If it blocks or breaks, the belt fails, causing heavy engine damage. In less critical modules the tension pulley can be replaced separately according to necessity. Nevertheless action should be taken at its first squeak. Also in the belt drive of the water or servo pump a critical situation is imminent when the tension pulley completely fails.
Defects of a tensioner pulley
As a rule, a defective tension pulley shows its malfunction by starting to squeak. This simple part is under permanent high strain, gradually wearing down its bearing. If this is ignored for too long, the pulley can jam. The belt grinds violently on the roll and soon ruptures, which makes itself heard by loud squeaking. Depending on which belt is affected, several symptoms can occur:
- Battery check light is on during driving: belt has become loose from the generator
- The coolant temperature is rising quickly: Water pump jams (Careful: engine overheating is imminent)
- Heavy steering: servo pump is failing
- Car stalls: timing belt rupture or injection pump jams.
This can cause high costs directly or indirectly. Tension pulley and belt drive are so cheap that adequate maintenance does not pose any problem.
Buying new tension pulleys
Costs for a new tension pulley strongly depends on which belt it is supposed to tension. For less critical modules, simpler and cheaper tensioner pulleys are used. For belts driving multiple modules, additionally responsible for valve duration, the tension pulley is critically important. Installing a cheap part of an unknown manufacturer is a very high risk. The quality of its bearings is not apparent on a cheap tension pulley, and they are the most important component. Only certified and tested quality can be allowed for a tension pulley. Otherwise an untimely failure could occur. Prices for new tension pulleys start at ca. 20 EUR (c. £18). High-quality tension pulleys with a complex mechanism can cost over 50 EUR (c. £45). Looking for offers in our shop is always worthwhile. We guarantee best quality and reliability on discounted products as well.