How To Diagnose Belt And Timing Component Failures

The timing belt is one of a few belts in an engine. At the front of the engine, you’ll see a plastic or metal cover. Behind it is a timing belt. Many current vehicles have switched to a timing chain, but these two parts perform the same function. Timing chains usually last the life of the engine, and this article does not apply to them.

The timing belt connects to the crankshaft and camshaft via several different pulleys. An engine has a timing belt for an important reason. The timing belt synchronizes camshaft timing with the crankshaft. If timed properly, this ensures that valves open and close in sequence.

Timing belt recommended change intervals can vary widely depending on the manufacturer. The recommended timing belt replacement intervals are from 60,000 miles to 100,000 miles. And you want to pay attention at anywhere from 50,000 to 100,000 miles. In most cases, timing belts go bad after 90,000 miles.

The Damage That Can Occur As A Result Of Timing Belt Failure

Timing belt failure

If a customer comes in with a higher mileage timing belt, or one with unknown mileage, it’s important to know how to inspect the belt correctly. Timing belt and timing component failure can lead to dire consequences.

When the timing belt fails, the valves will no longer open and close at the proper time. It’s possible for a valve to come in contact with a piston. It’s because when a timing belt fails, the pistons move in the cylinders until they either run out of momentum or hit the valves. All this leads to engine damage. In some cases, complete destruction of the cylinder head is possible too.

So if you neglect to inspect the timing belt and warn the customer, and it fails, your shop can be on the hook for expensive engine repairs.

Signs Of A Failing Timing Belt

When timing belts get old, they can fail in one of two ways. They can snap, or they can stretch enough that they slip on a toothed pulley. If they snap, the engine won’t run and there may be severe damage. If they slip, the timing will be thrown off. Some symptoms of a slipped timing belt include:

  • Sluggish acceleration, or no acceleration
  • Difficulty starting the engine, sometimes after stopping the car
  • Stalling engine
  • Shaking engine

Inspecting The Timing Belt

Inspect timing belt

First, you want to confirm that the timing belt has failed.

The timing belt is in front of the engine. You’ll have to remove the timing belt cover to see it. Grab a flashlight and then give the timing belt a visual inspection.

Check for any fraying or cracking on either side of the belt. Next, check the timing belt tension either by hand or with a timing belt tension gauge. This guide will walk you through the process of checking the tension. Knowing the timing belt tension may give you an idea of what went wrong.

If there are any obvious abnormalities, replace the timing belt. In some cases, only replacing the belt isn’t enough. You would need to check all the other timing components, as well.

Checking All The Timing Components In The Engine

Sometimes the timing belt doesn’t fail due to age or excessive wear. Sometimes it fails because another component has failed. If you don’t check the timing components, and if one of them is bad, the next timing belt will fail too.

Here are the timing system components you need to check:

  • Timing belt tensioner
  • Pulleys (including the timing belt idler pulley)
  • Cam seals
  • Crank seals

Make sure each part is functioning as it should. If you find an issue with any of these parts, you’ll have a clear idea of why the timing belt failed.

At this point, you have a clear idea of what went wrong. Maybe the timing belt itself failed due to age or excessive wear. Or maybe a timing system component failed and caused the timing belt to fail. Either way, it’s time to explain to the customer what happened and what needs to be done to fix the situation. This guide can help you navigate this topic with the customer.


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