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1. Function

V-belts are responsible for transmitting the rotational force of the crankshaft to components such as the cooling water pump which cools the engine, alternator which generates electricity, and the air conditioner (A/C) compressor.

  1. Crank pulley – This pulley is connected to the crankshaft and transmits motive force to various components through the V-belts.
  2. Alternator – This is a generator that produces the electricity used in a vehicle.
  3. Water pump – This is a pump that distributes coolant to various parts of the engine to keep it cool.
  4. A/C compressor – This device sends A/C refrigerant to the unit.
  5. Idle pulley – This pulley is used to adjust the tension on the V-belts.

2. Construction

This illustration shows the cross section of a V-belt

  1. Top fabric – This fabric protects the belt from heat and oils.
  2. Tension cords – These maintain the belt at a consistent length.
  3. Cushion rubber – This holds the tension cords in place.
  4. Compression rubber – This is the main portion of the V-belt.

3. Types

There are four different types of V-belts depending on where they are used.




Standard V-belt

Good power transmission and wear resistance


This type consists of several standard V-belts integrated into a single belt. Good durability and is used for high horsepower and high torque applications.

Cogged V-belt

In addition to having the characteristics of standard V-belts, this type of belt offers good flex resistance and longer life cycle.

V-rib belt

Thinner than standard V-belts, these high-performance belts provide greater flexibility, better engagement with pulleys thanks to their grooves, and also better power transmission. They also produce less noise and vibration, and are suited for
high-speed high-load transmission applications.

4. Differences between genuine and aftermarket parts

Genuine belts are made by layering special synthetic rubbers with high-tensile tension cords and therefore provide lower stretch rates. Additionally, they are able to transmit driving force more precisely to other axles because their sides are not lined with a jacket. Meanwhile, aftermarket parts, although they may appear to be rigid and robust as their entire perimeter is wrapped in jacket fabric, fabrics have a lower transmission efficiency than rubber. Additionally, the jacket fabric on some products may degrade after long-term use and this can lead to shorter life times as well as make the rubber material more susceptible to degradation from heat and/or oil over cycle.



Aftermarket parts



Special synthetic rubber

Synthetic rubber

Side jacket fabric

Not used

Used (wound)

Service life ratio



5. The importance of maintenance

If the V-belt loses its tension and begins to slip, the coolant pump may lose its ability to pump coolant, which in turn can cause the engine to overheat or seize. If the alternator is unable to generate electricity, this will drain the battery and render your vehicle inoperable. If the V-belt breaks, the different components can run idle or stop, which may cause serious problems, including serious injury by flying shards from broken parts.

Engine overheat

Service truck assistance

Vehicle down

Because V-belts are made of rubber, regular inspections and servicing is critical for avoiding problems such as those listed above.

Examples of inspection items

(See your User’s Manual for details)

1. Belt tension

1. Is it stretched and slipping? Is it too tight and putting too much stress on the components? (See Image 1)

2. Belt grime

2. Is the belt soiled with oil, etc?

3. Belt wear

3. Are the tension cords exposed? Is the top or bottom fabric coming off?

4. Pulley groove wear

4. When you check the belt, make sure to check the grooves on pulleys for wear.

Inspecting belt tension
Press the middle section of the belt with a force of about 10kg, or measure it with a special compression gauge.

Caution! When replacing V-belts, never use belts that are different from the ones installed on your vehicle. This is critical for getting the maximum performance from your Hino vehicle.