What Is a Timing Belt Tensioner?

by William Norman

An automobile engine demands the utmost precision from the interaction of its many moving parts. The slightest timing errors between valves and pistons can spell disaster, leaving the driver stranded with a destroyed or unresponsive engine. The parts that keep an engine running in perfect synchronization include the timing belt and the timing belt tensioner.

The Timing Belt

Valves and pistons must work together with perfect timing for a car engine to do its job properly. The timing belt ensures that the camshaft spins at precisely half the speed of the crankshaft, allowing the camshaft to operate the intake and exhaust valves in perfect synchronization with the motion of the car's pistons, according to Family Car Parts.

Tensioner Functions

The timing belt tensioner maintains the correct level of tension on the timing belt to keep it moving in perfect synchronization with the other parts of the engine. According to the Repair Pal website, a tensioner consists of a lever attached by a shaft to a housing that contacts the belt. Springs near the tensioner allow it to exert force against the lever, which responds by adding the right degree of tension to the belt via a pulley.


The tensioner pulley must exert a consistent tension on the timing belt to ensure correct engine operation. Family Car Parts warns that if the timing belt slips in its timing by even a single notch, the piston may strike a valve, bending the valve and possibly breaking both components. This turn of events can occur easily in an "interference engine," which places the pistons and valves at close quarters to each other. A "non-interference" engine will not suffer fatal damage to improper tension and timing, but it may suddenly stop working.

Maintenance & Replacement

According to Family Car Parts, timing belts require replacement at certain intervals in the car's life span. These intervals may vary from 60,000 to 105,000 miles, depending on the belt type and car model. (Timing chains do not require replacement, according to Popular Mechanics.) The tensioner can wear out over time, so Family Car Parts recommends that the auto shop replace the tensioner at the the same time as the belt. When the tensioner receives the new belt, the belt must align perfectly with timing marks on the engine so that the cylinders and valves work together in proper order.


Sensible repair strategy often involves replacing multiple components that tend to wear out at approximately the same time, because the customer can save labor costs by having all the work done in one visit to the shop. AA1Car.com notes that timing belts, tensioners and water pumps fall into this group, adding that placing a new timing belt on a worn tensioner may simply cause another belt failure.

About the Author

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Photo Credits

  • photo_camera Image by Flickr.com, courtesy of Sabrina