The High Cost Of Putting Off Idler Pulley Or Belt Tensioner Replacement

A worn timing belt tensioner or idler pulley can be a ticking time bomb for an engine. If either part fails, it can cause the camshafts and crankshaft to rotate out of sync. This can cause catastrophic engine failure and very expensive repair costs.

Interference Vs. Non-Interference Engines

There are two fundamental types of engine valve trains, called interference and non-interference. The difference is defined by what happens if the engine loses its timing. This is usually due to a timing belt breaking. Let’s take a look at what happens in each type of engine when a timing belt breaks:

  • In an interference engine, there is valve-to-piston contact in the engine. If the timing if off, severe engine damage from bent valves and broken pistons is likely.
  • In non-interference engines, there is no valve-to-piston contact within the engine. There may be visible machined relief areas on the tops of the pistons for the valves to clear. There is usually no damage to the engine if a timing belt goes.

You may be wondering why interference engines exist if they are susceptible to damage in this way. The answer is that the interference engine design typically allows higher compression ratios, which produces more power, and is, therefore, more fuel efficient. Most engines made today are interference engines.

What Is A Timing Belt Tensioner?

A timing belt tensioner keeps the timing belt pressed tightly against several pulleys, including:

  • Camshaft Pulleys
  • Crankshaft Pulley
  • Water Pump Pulley
  • Idler Pulleys

There are marks on the teeth of the crankshaft pulley and the camshaft pulleys. These marks are aligned precisely with the grooves in the timing belt for correct engine timing.

Timing Belt Tensioner Problems

There are several possible symptoms of a failing timing belt tensioner. Some symptoms are gradual while others are very sudden. Noticing the early warning signs is critical to avoiding expensive engine repairs. Here are the common symptoms:

  • Check Engine Light -The check engine light may turn on because of problems with engine timing and misfires.
  • Engine Performance Issues -The engine may run rough or exhibit a loss of power because the engine timing is incorrect.
  • Engine Not Starting -The engine may crank but not start because the valve timing is off or engine damage has already occurred.
  • Engine Noises – A failing timing belt tensioner may grind from a bad bearing or rattle from losing tension against the belt.
  • Engine Failure – A broken timing belt tensioner may cause the belt to slip, throwing off the timing. If the pistons contact the valves, catastrophic engine failure will occur.

What Is An Idler Pulley?

A timing belt idler pulley stabilizes and routes the timing belt around the toothed gears of the crankshaft, camshaft, and water pump pulleys. A vehicle can have more than one idler pulley, depending on the size of the engine and the length of the timing belt. A failing timing belt idler pulley may grind or rattle if the bearing becomes worn. Excessive play in the idler pulley rotation may also cause the timing belt to slip off. If this happens, the engine will stop suddenly. Severe engine damage will occur if the pistons contact the valves.

Diagnosing Timing Belt Problems

Need more help on how to diagnose or inspect your timing belt, tensioner, or idler pulley? Have a look at our comprehensive blog post, Is It The Timing Belt The Tensioner Or The Idler Pulley? ANd when you’re ready to purchase new timing belt parts, discover why you should choose GMB tensioners and idler bearings.

GMB Offers Quality Parts You Can Trust

Timing belt tensioners and idler pulleys are important parts of a perfectly syncronized system that keeps your engine running. Trust GMB for these parts and more because:

  • We are an industry-leading manufacturer of both OEM and Aftermarket automotive parts since 1943.
  • We have locations on both the east and west US coasts, and global locations in Asia and Europe.
  • We’re here for you! If you have any questions about our products, please contact us.


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