How to Check V-Belt Tension Calculation

The V-belts on a vehicle or generator function as the driving mechanism to connect two or more pulleys. The driving pulley supplies the power to rotate the driven pulley, which usually consists of a component or accessory. Common V-belts can be seen on automotive generators, water pumps, AC compressors and power steering pumps. Calculating the V-belt tension keeps the belt in constant contact with the pulleys to maintain the driving force, as well as providing a pulling torque that will not damage the accessory or component bearings. A vehicle owner can successfully calculate belt tension with the use of a belt tension gauge.

Instructions

1

Place the vehicle transmission selector in "Neutral" for a manual or "Park" for an automatic. Apply the emergency brake. Raise the hood. As a precaution, remove the negative battery cable with a socket and wrench. Use a rag to wipe down the pulleys and belt you wish to check. Remove any signs of grease, water or oil from the belt and pulley grooves.

2

Measure the longest span of the belt between the points where it connects from one pulley to the next; this is the belt free span that does not contact the pulley surfaces. Use a tape measure to record the total length in inches, and record it with pencil and paper. Add 1/64 inch for every 1 inch of the total belt span. For example, if the belt span measures 32 inches, 1/64 times 32 will equal 1/2 inch. The deflection for this belt will be 1/2 inch.

3

Set the large O ring on a belt tension gauge at the 1/2-inch mark. The large O ring sits on the non-plunger side of the gauge---move the rubber O ring up the shaft a distance of 1/2 inch. Set the smaller O ring on the plunger side of the gauge to the "0" mark. Hold the tension gauge perpendicular to the belt and push the plunger head of the gauge down into the middle span of the belt until it reads 1/2-inch deflection on the gauge scale.

4

Lay a straight-edge ruler over the top of each pulley while pushing down on the gauge. Determine if the reading on the scale exceeds 1/2-inch deflection, or if the belt deflects under this amount. If the measurement reads more or less, you will need to loosen the mounting and adjusting bolts to the component or accessory and either tighten or loosen the tension on the belt. Recheck the measurement with the belt tension gauge.

5

Calculate the belt deflection manually by using two straight-edge rulers. Sit one ruler across the top span of both pulleys, and hold the other ruler perpendicular to the top ruler. Push your thumb down against the widest span of the belt and note the inches the belt moved inward, according to the second ruler. Adjust as necessary, according to the manufacture's specifications in your owner's service manual. Manual belt deflection can range from 1/2 inch to 5/8 inch, depending upon the engine model. Reconnect the negative battery cable with a socket and wrench.