How To Adjust Fan Belt Of Any Car Engine

How To on Fan Belt Of Any Car Engine

 How To on Fan Belt Of Any Car Engine
How To on Fan Belt Of Any Car Engine


Though fan belt may not drive a radiator cooling fan on most water-cooled engines, it drives the water pump. In an air-cooled engines, it often drives the fan that blows air through the cooling fins. In either instance, the fan belt helps in the cooling system of engines hence if it breaks the engine will suffer overheating.

Fan belt stretches a little in service and should be checked for damage and correct tension at each service interval. Proper tension is important. An over-tight belt will put too much strain on the bearings of the water pump and generator, while a loose belt will slip and in time the battery will go flat because the generator is not turning fast enough.

Methods of tensioning a slack fan belt vary; on most engines the generator is moved away from the cylinder block to take up any slack. On a few cars, however, the generator is fixed and on these a split pulley is used to adjust belt tension.

Removing spacers from the center of the pulley makes the belt run nearer the edge and increases the tension. If the belt cannot be tension fully, it has stretched and must be renewed.

When fitting a new belt, slacken off all the tensioning adjustment and fit it on the pulleys by hand, taking care not to twist the belt. Once it is fitted to all pulleys, tension it.


1.       First twist the belt and look for cracks or cuts on the vee-section that touches the pulleys. If it is damaged, fit a new belt.

2.       If the belt is sound, see the car handbook for the correct method of checking the tension. If one is not mentioned press the belt firmly mid-way between the two most widely spaced pulleys; there should be about ½ in (12mm) deflection in the belt.

3.       If your car has an unorthodox fan belt arrangement, as on the Peugeot 104, you must check the maker’s recommended tensioning system. Tension is correct when there is approximately 5/8 in  to ¾ in (15mm-20mm) between the belts when they are squeezed together firmly.


A.      Where the generator tensions the belt, use two spanners to loosen the hinge fixings, and slacken off the clamping bolt.

B.      Swing the generator away from the engine to tension the belt. Use a wooden lever (a hammer handle will do) between the generator and engine block to get the right tension.

C.      While the belt is held under tension, tighten the clamp bolt. Re-check the tension and if it is correct, re-tighten the hinge fixings.

D.      On cars with split pulley adjustment, undo the nuts holding the pulley together and take off the outer half.

E.       Remove one packing piece from the center and refit the outer half, with the displaced packing piece on the outside; re-tighten the nuts, taking care not to trap the fan belt near the hub.

F.       With the pulley assembled, rotate the engine one revolution before checking the tension.


i.                     Loosen all adjustments, remove the old belt, and put the new one over the pulleys by hand. It helps to hoop the belt over the crankshaft and generator pulleys first, and to rotate the water pump pulleys to “wind on” the belt in the same way as one fits a bicycle chain. Do not use a screwdriver or sharp implement to lever on a tight belt. If it does not fit bi hand, the belt is a wrong size, or all the adjustments have not been fully slackened off.

ii.                   Some cars have a close-fitting shroud round the cooling fan. On these a small cut-out provides just enough space to threads the belt over the fan, one blade at a time.

iii.                  With split pulley adjustment, first fit the belt with all the spacers between the pulley halves, then if necessary, subtract spacers until the correct tension on the belt has been obtained.

iv.                 All new belts stretch a little when first used and the tension should be re-checked after 100 miles, or sooner if stated in the handbook.

Philip Nduka

Philip is a graduate of Mechanical engineering and an NDT inspector with vast practical knowledge in other engineering fields, and software.

He loves to write and share information relating to engineering and technology fields, science and environmental issues, and Technical posts. His posts are based on personal ideas, researched knowledge, and discovery, from engineering, science & investment fields, etc.

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