Timing Belt, How Do I know It Needs Replaced?

We use to check for timing chain and gear wear by using a timing light to measure timing variations at different rpm settings or check the stretch by counter rotating the crankshaft with the engine off. However, neither of these tests is practical today, even on engines with a timing chain as the PCM is constantly adjusting the timing and the chains have guides made of plastic that will be damaged with a stretch test. Checking the stretch on a timing belt is a No-No as it will most likely result in belt damage.

The economy is causing more people to purchase older vehicles and this is creating a problem for those people. The problem it creates is a lack of knowledge as to what or when maintenance has been performed on the vehicle, and specifically the timing belt.

Most of these used vehicles no longer have the owner’s manual or guide as some manufacturers call them. Therefore, the used car purchaser has no way to reference the maintenance schedules posted in those guides. In addition, these guides are out of date when printed as the manufacturers change maintenance intervals based on feedback from their service departments.

It would be nice to think that the used car dealer performed all the required maintenance on the vehicle prior to the sale, but the sad truth is most used car dealers only wash and clean the car, like a "lady of the evening preparing for work". Some will do simple obvious things like change oil, replace a burned out bulb, or an extremely worn tire. Very few perform any more maintenance than this, and that includes many franchised new car dealers.

Most likely, this new ‘used’ vehicle has a timing belt that was supposed to be serviced at specific mileage intervals. That mileage interval is 60,000 miles on most vehicles to 100,000 miles on others. Failing to replace the timing belt at the proper interval can result in catastrophic damage to the engine and of course bills to match.

So how do you protect yourself?

The best protection, if possible is to obtain those maintenance records from the previous owner. If this is not possible then your only other options are either to replace the belt and the normally wearing components or to trust your luck. The later unfortunately has never worked very well for me and probably not for others.

You could pay a mechanic to inspect the belt, but unless the belt is literally ready to break, it is almost impossible to tell without removing it. Therefore, the only real option is to replace the belt and the normally wearing components.

The normally wearing components are things like the idler pulley, the tensioner pulley, the water pump, the other timing belts that may be there for balance shaft, oil pump, and the oil seals for the camshafts and crankshaft, etc. Many people in a tight financial condition want to eliminate these extra wear items but this to coin an old phrase is ”Penny Wise and Pound Foolish”.

Let us assume your car has its water pump driven by the timing belt, and you choose not to replace the pump to save money. When your mechanic replaces the timing belt, the torque on the water pump shaft changes, simply from a properly installed belt. This means that more than likely the seals in it will start to leak coolant onto the new timing belt, which will destroy the belt and allow it to break which in turn causes the catastrophic damage that you were attempting to avoid.

This same scenario can happen because of a failed camshaft oil seal. Therefore, to save perhaps $5 or $10 on a seal and a half hour additional labor you are risking possibly thousands of dollars. Not a good bet, right?

Here is a timing belt diagram of a 2005 Kia Sedona 3.5L v6. This engine’s recommended replacement interval was 100,000 miles which has been reduced to 60,000 miles by Kia Motors of North America. You can clearly see all the normal wearing parts that should be replaced during the timing belt service. Do you personally want to attempt a belt replacement like this in your home garage?

timing  belt diagram and components of 2005 Kia Sedona with 3.5L v6 engine

Remember that if purchasing this used vehicle without maintenance records, you should adjust your offer to reflect the needed maintenance cost. If you have owned your car since new, check with your mechanic about the current recommend service interval from the manufacturer. Do not simply guess. Check the data.

Does this only apply to timing belts?

No, there are several documented engines with timing chains that should be replaced at intervals. These are engine like the Nissan VQ engine, the Chrysler 2.7L v6 and others. For instance the Chrysler 2.7L v6 has guides for the timing chain  made of ‘plastic’ when these guides fail they allow the camshafts to get out of time with the crankshaft and valve to piston collisions occur.

For the Professional

When you perform this service take the time to properly clean all the timing belt covers and check the dust seals. Cleaning these normally does not require much time or materials. Most times the clean up can be performed using a spray mister filled with water. If your customer is not allowing you to replace the normal wearing components, be careful about getting any moisture around the idler and tensioner pulleys as their bearing seals can not be trusted.

If these covers are full of oil, replace the oil seals or make notes that it has oil leaks.Remember that the timing belt is a 'dry' running belt that can not tolerate oils, liquids of any kind, nor can it tolerate dust.

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Enhanced Software Included
Phone Tablet PDA Capable
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2 Wheel Vehicle Applications
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All above information is based on published information as of 01/2015 or products purchsed to confirm

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