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Your Pulley (v belt pulley) worn out? » Read more about common malfunctions • Repair • Replacement manual
Transmitting basic torque: the belt pulley
The V-belt pulley is a simple component and has been around since the dawn of car manufacture. It transmits and receives torque and engine speed for powering auxiliary units. The belt pulley is gradually being replaced by the flat belt pulley, as modern units need to provide higher rotation speed whilst maintaining the same size.
Minimal width with maximum surface
Space is narrow in an engine compartment. Sometimes efficient car construction comes down to the millimetre. For this reason the V-belt was developed. The V-belt, i.e. a rubber belt with wedge-shaped diameter offers a narrow profile with ample surface. A V-belt transmits torque with friction locking. It is tensioned between two belt pulleys. When the transmitting and the receiving belt pulleys are the same size, rotation speed and torque are transmitted 1:1. In most cases a gear ratio change is effected by using different diameters of a larger and smaller belt pulley.
Location of the V-belt pulley
There are two plausible locations for a V-belt pulley in a car engine. Usually, it is flanged onto the crankshaft. In some cases the V-belt pulley is found on the camshaft or somewhere else in the engine connected via a spur wheel drive. The pulley is small, as a low diameter saves space. Also, the small dimension is ideal for effecting a higher rotation ratio. The receiving disc is found on the auxiliary units, such as:
- water pump
- servo pump
- coolant compressor
By installing a larger belt pulley on the auxiliary units the higher torque of the engine is converted to a higher rotation at the aggregate. This is exactly what aggregates need: the faster alternator, water pump, servo pump or coolant compressor run, the more effective they perform.
V-belt pulley: defects
The V-belt pulley is a very robust component, often lasting a car's life span. When something in the belt drive fails, the V-belt is bound to follow soon. By a faulty installation of the belt, excessive tension or an imbalance of the transmitting or receiving shaft, the V-belt pulley can become a stroke or bend. As a result, the V-belt either wears quickly or slips off continuously. It is therefore important to find the exact cause for a defective V-belt pulley. It is often an indication of potential larger damage.
Consequences of defective V-belt pulley
The transmitting V-belt pulley is fixed to the camshaft or crankshaft. If it is fixed with only 1 central bolt, it usually has a left thread, preventing the bolt from loosening during operation. To make sure, V-belt pulleys were often fixed with three or more bolts. Replacement is just as easy. A V-belt pulley, however, usually breaks down as a result of excessive tension of the belt drive. This excess tension does not affect the engine bearings, although the O-ring can sustain damage as a result of the erratic tension. When the V-belt pulley has become too oily, the gasket of either camshaft or crankshaft must be replaced. The excessive tension of the belt drive can affect the bearings at the receiving end. Therefore, water pump generator or servo pump should be tested for a smooth, running, free of jolts, prior to installing the new V-belt pulley.
V-belt pulley repair
The V-belt pulley hardly ever breaks down. When it has to be replaced, both pulleys and the belt should be renewed. Even when bearings and seal rings are in good order, a replacement of all components re-establishes a new condition for the whole system. Hidden or gradual damage can thus be avoided before new components sustain damage. It is very important always to use fitting components. A visual estimate will not do. V-belt and pulley must be a total match, otherwise a higher wear is preprogrammed. The spare part is not particularly expensive: a belt pulley for the V-belt costs starting at 7 EUR (± £6).