Why the timing belt breaks: 6 main reasons

by | Tips

Why the timing belt breaks is a question that haunts many drivers. Replacing this unit is often expensive, and its wear can occur for various and often simply unknown reasons. Let’s say right away: a breakdown is usually a whole series of factors that drivers initially overlooked.

What is a Timing Belt?

The timing belt is an indispensable part of the power unit, providing synchronization and orderliness in the operation of the camshaft and crankshaft. Thanks to this element, each valve opens and closes when needed.

A whole, unworn belt allows the camshaft to rotate at a set speed half that of the crankshaft. When the camshaft spins, an air-fuel mixture (AFM) enters the engine cylinders, and the exhaust gases are discharged through an interconnected system.

The use of the belt became possible after the manufacturer asked to create an engine with less weight and price. In addition, it was possible to significantly reduce the noise generated during the operation of the power unit. But all costs were borne by the consumer. Changes associated with the advent of the timing belt have caused some difficulties in service and replacement. The belt drive cannot last a long time; therefore, it is necessary to constantly monitor its condition and tension on such engines.

The designers hoped that the timing belt’s strength, elasticity, and durability would be close to the chain when making the changes. After several attempts and experiments, the timing belt began to be made in three layers.

Six main reasons why the timing belt breaks

Most often, this occurs due to reckless operation or other engine malfunctions, in which the described situation refers to the consequences rather than the causes.

1. Factory defect or a belt of inadequate quality

Some motorists are sorry to spend money on a replacement. Most manufacturers advise replacing the timing belt after the car has driven 60-70 thousand kilometres, which beginners do not pay enough attention to. There are times when the wear or stretching of this element contributes to slippage or breakage.

Do not forget that it is better not to purchase this part in cheap stores. By opting for the original, you are giving money for a belt that contains a high-strength steel cable in its structure. This approach prevents the belt from stretching and tearing. Using a fabric cord in non-original products reduces its service; a timing belt breaks faster.

That is why manufacturers from European countries, as well as from Japan and America, install only high-quality parts on their cars. If you choose cheap replicas, be prepared for an early breakage and damage to the belt.

2. Violation of operating rules

The following reasons contribute to the breakage of the timing belt:

Fast starting from a standstill or abuse of engine braking. A critical moment with sharp acceleration can deform the part.
Antifreeze or oil on the belt. If grease gets on the rubber, it can cause slippage, bouncing through the gear teeth and cause the material to burst. Incorrect drive alignment. Improper installation of the idler pulley can place excessive stress on the belt, causing rapid wear.

3. Normal wear and tear

One can single out natural wear and tear among the main reasons why the timing belt often breaks. Without changing the strap in time, every motorist creates the likelihood that it can fail.

Install the new element per the manufacturer’s recommendations. It is highly undesirable to use a car that has passed the timing belt replacement period.

4. Defective pump

Many cars are designed so that the coolant pump rotates from the timing belt. Therefore, a faulty pump can also lead to a broken belt. The timing belt will break if the pump stops spinning (jamming).

The pump has a hole on its body that allows you to determine the degree of its wear. The presence of coolant in it indicates that you must replace the unit. But some craftsmen manage to screw a bolt into it, thereby getting rid of the drops, and continue to use the car as if nothing had happened. On a domestic vehicle, you can find such a picture most often.

5. Errors when installing the belt

Incorrect installation can cause the belt to break. Here are some examples:

Over-tensioning the belt will shorten its lifespan. The pump, driven by the belt, will “howl” if overstretched and my jam.
Loose bolts on the idler pulley or the crankshaft and camshaft pulley can come loose. If, on the contrary, you overdo it when tightening the stud, for example, on the tension roller, this will lead to its deformation. The position will change about other elements, and the belt will begin to slide out.

6. The belt may break even if you try to start the car from the pusher.

Also, in this case, there is a possibility of shearing the belt’s teeth, clipping the flywheel mounting bolts, breaking it, etc.

Signs of a broken timing belt

A pop often accompanies a broken belt, and the engine stalls, with all other parts usually working. You can hear a metallic knock when you start the engine while the starter rotates easily because there is no compression in the cylinders. But do not try to start the engine if you suspect a possible belt break. It is better to scrutinize everything first.

When the engine is restarted, the most severe consequences are accompanied by a metallic knock somewhere in the engine area.

Consequences of a broken timing belt

Having answered the question of why the timing belt is constantly breaking, it is possible to disassemble the problems caused by this ailment, namely:

Damage resulting in deformation of the valves. When the crankshaft and camshaft rotate asynchronously, the pistons collide with the valves. As a result, these parts are damaged, and an engine overhaul becomes necessary. Otherwise, the motor will have to be thrown away.
If the consequences are minor and the central units remain intact, the repair will only replace the belt and adjust it.

Let’s consider some points in more detail. The situation with a break in the timing drive and its danger depends on the design of the engine and the conditions in which it failed:

A break in the timing belt leads to a stop of the camshaft. As a result, the valves freeze and stop moving. But by inertia, the rotation of the crankshaft continues, the pistons hit the open valves, and they bend. Some types of engines installed on VAZ 2111 cars, for example, have special recesses on each of the eight valves, which exclude contact with them when the belt breaks. You will not find such manufacturing features in modern engines since manufacturers strive for maximum power while maintaining a small volume.

Suppose a situation arises when the timing belt breaks at idle engine speeds, only a couple of valves can suffer. Also, guide bushings can deform at a high rotation rate of the crankshaft. Such consequences entail the need for an overhaul of the engine or replacement of the cylinder head.

A break in the timing belt on a diesel engine will deform the valves, camshaft, bearings, blockhead, connecting rods, and pushers. The reason lies in their design, which is characterized by the lack of valve free play when the piston is at the top dead centre.

On Japanese engines, a broken timing belt is accompanied by the failure of all valves, breakage of bushings, pistons and blockheads. All this is typical at high speeds.

Timing belt replacement frequency

Even in cases where the engine is working perfectly, do not forget about the need to monitor the condition of the timing belt because it also does not last forever. The mileage is indicated in the car’s technical passport, after which it is necessary to replace the part. But you can do it differently: install a new belt every 50 thousand kilometres.

If you purchased a used car, and the seller did not give any information about the date of installation of the timing belt, then inspect it. The presence of microcracks on the case is a reason to think.

But do not worry too much, since microcracks only inform you that the unit requires attention, but it is unlikely that it will break off at the first start. Inside the belt, there is a metal base made of thin rods. This contributes to the fact that it can withstand large starting loads and not break off for long.

There are cars that the manufacturer completes with shock-resistant belts with a reinforced metal cord. Thanks to this approach, the operational life is increased by about one-third.

Instructions on how to proceed if the timing belt breaks

If the timing belt breaks, you should adhere to the following order:

  • Raise the hood and move to the side (or remove altogether) the cover that protects the mechanism.
  • Next, you should visually inspect the belt (the breakage point will immediately catch your eye). If the break occurs at the bottom, then, to see it, you will have to crank the crankshaft half a turn.
  • The next step is to move the car to a garage or service station by towing it. When an automatic transmission is installed on the vehicle, you will have to call a tow truck since it is strictly forbidden to tow such cars.


Can you fix a timing belt yourself?

It depends on the car. Some models are relatively easy to work on, while others can be more complicated. If you’re not sure whether or not you can fix it yourself, it’s always best to consult with a professional.

What does a timing belt do?

A timing belt is responsible for synchronizing the many parts of an engine. Each piece is responsible for a different task, and if they don’t work together in time, the car can become severely damaged.

How much does it cost to fix the timing belt?

The labour cost can vary, so it’s best to check with a few places before settling on one. In South Africa, expect to pay between R 1 800,00 to R8000,00.

How do I know if my timing belt is terrible?

When the engine is running, you’ll notice it and hear a rattling noise. If your timing belt breaks, there’s a good chance the engine will be severely damaged or eradicated. The car won’t run without a functional timing belt.

Can I drive if my timing belt needs to be replaced?

It’s not recommended. Driving with a broken timing belt can cause extensive damage to your engine. If you’re not sure whether or not it needs to be replaced, it’s best to take it to a mechanic and have them look.

Can you splice a timing belt?

You can, although it’s not recommended. The belt may run rough or not if you try to splice one together. It’s best to buy a new one.