In a car or other machine’s power transmission belt system, the V-belt is the rubber or polymer pulley that transfers force from the engine to other vital components, such as a car’s alternator, power steering pump, or air conditioning compressor. These belts get their name from their cross-section trapezoidal or V-shaped ridges, which fit into a groove on the pulley and wedge as the engine’s load increases. Among the various belts used in the operation of engines, V-belts are known for their solid traction and transfer of speed to components, as well as their long service life.

Of course, no components last forever. If you notice a squealing noise, that could mean your V-belt is worn or cracked from years of use, causing it to slip from its grooves, or even snap entirely. When this occurs, it’s time to invest in a new belt.

V-belts come in a variety of types, including: 

• FHP (Fractional Horsepower) belts are typically used in very low horsepower applications, such as fans.
• A - E belts are used in medium horsepower machines with single-belt and multi-belt drives.
• AX, BX, and CX belts are for medium and high horsepower industrial applications and single-belt and multi-belt drives.
• 3VX and 5VX belts are often used with high horsepower engine drives.
• Banded V-belts provide enhanced stability and load distribution that’s ideal for heavy-duty machinery.
• Micro V-belts have a narrow profile that’s suitable for compact systems such as automotive engines.
• Cogged V-belts feature a toothed design for improved grip and reduced slippage in high-torque applications.
• Link V-belts are versatile, easy to install, and suitable for various types of machinery.
• Multiple V-belts utilize several V-shaped grooves for increased power transmission efficiency. 
• Metric V-belts adhere to international sizing standards, ensuring compatibility across equipment.
• Double V-belts provide traction with two V-shaped surfaces, suitable for demanding industrial environments.
• Variable-speed V-belts offer adjustable performance and are adaptable to fluctuating operating conditions.

V-belts and serpentine belts are both used for power transmission in vehicles and machinery, but they have different designs and applications. Let’s take a look at their features. 

V-Belt:

• Consists of multiple V-shaped grooves on its inner surface.
• Typically used in older vehicles and machinery.
• Often found in systems requiring high torque, such as industrial machinery.
• Generally requires more maintenance and adjustment compared to serpentine belts.

Serpentine Belt:

• Singular, flat belt that wraps around various pulleys in a serpentine pattern.
• Used in modern vehicles and machinery due to their efficiency and simplicity.
• Serves multiple components such as the alternator, water pump, power steering pump, and air conditioning compressor.
• Generally offers longer service life and requires less maintenance than V-belts.

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V-belts are typically found on one side of the engine block. Look for the belt looped around two pulleys and overlapped at a single point to resemble a V-shape. To remove the V-belt, you’ll need to adjust the position of one of the pulleys to release some tension. This can be done by turning the pulley counter-clockwise with a wrench. Once you remove the old belt, you’ll need to get a new one that fits exactly right—with the same width and length as the original—or it won’t function properly.

The best way to ensure you order the proper replacement part is to look for the OEM (Original Equipment Manufacturer) number on your old belt. However, if this number is worn down on the belt itself, or if you are installing the part for the first time, you’ll need to take a few measurements to determine the correct belt size.

• Top width and height
• Length (outside circumference)

The top width and height can be measured using a tape measure. Simply measure from the 1" mark across the top of the belt. Common widths range from ½" to as wide as 1½" to indicate whether you need anything from an A-belt all the way up to an E-belt.

You can measure the length of a V-belt in a few different ways. The easiest way is to use a specialized belt measuring tool, which features two jaws: one fixed and the other moveable. Put the belt in the fixed jaw of the tool with the V-section pointed downward and loop it around the moveable jaw. Push the moveable jaw downward until the belt goes from loose to tight, and check the reading, usually found in the lower right or left corner.

The next best way to measure a V-belt is to use something soft that will easily wrap around the component’s contours. Options include a soft ruler, fabric tape, or even a piece of string. Just wrap the ruler or fabric tape around the full circumference of the belt to figure out the length. If you’re using a piece of string, make sure the two sides meet at the beginning mark, and then measure the string with whatever tape measure is available.

If all you have is a hard ruler or tape measure, you’ll need to use a heavy-duty marker to indicate a point on the outside of the belt. Then, with the hard ruler lying flat on a counter or tabletop, measure starting at the marked point and roll it along the ruler's length until you complete a rotation. The endpoint of the rotation will indicate the measurement of the belt.

Keep in mind that wear and tear can cause V-belts to stretch out. Make sure to consult the list of common V-belt sizes below and adjust accordingly if your measurement does not match one of the standard sizes. If you are working with a stretched or elongated belt, you may need to adjust to a slightly shorter length to ensure the proper tightness is achieved.

These dimensions are standards often found in industry catalogs. Belt lengths can vary and are usually specified separately. This table includes the most common belt types, but there are many other specialty and multi-groove V-belts used for various applications that are not included here.

This chart serves as a guideline for identifying and selecting the appropriate belt for mechanical and industrial applications based on size and type. Always ensure that the belt dimensions align with the specific requirements of the machinery or application for optimal performance and durability.