The job of a timing belt and timing chain stays the same, although they look different and have different positions in an engine. They both connect the engine’s crankshaft to the camshaft, controlling the pistons and valves, making sure they operate precisely when they need to inside your engine’s cylinders.

Rubber timing belt

The most obvious difference between the two is that a timing belt is made out of rubber and the chain is metal.

Camshaft drive chain
Metal timing chain

A timing belt, also called cam belt, and timing chain is a part of an internal combustion engine and their main job is to synchronize the rotation of the crankshaft and the camshaft(s) so that the engine’s valves open and close at the proper times during each cylinder’s intake and exhaust strokes. In an interference engine the timing belt or chain is also critical to preventing the piston from striking the valves. A timing belt is usually a toothed belt—a drive belt with teeth on the inside surface. A timing chain is a roller chain—using a chain drive.

Main timing system components

Except for the timing belt and chain, there are other components considered to be necessary for the timing system to function properly. These components include:  

Camshaft pulley


Idler pulley


Tensioner pulley


Crankshaft pulley


Water pump


A cam pulley is used to control the speed of the camshaft. This is the timing belt component that controls the poppet valves responsible for the exhaust and intake of air in the cylinders. The cam pulley is pivotally connected to the timing chain to rotate the camshaft in sync with the crankshaft. 

The timing belt idler is a pulley that helps to set the timing belt in the correct position. If the chain/belt and engine is bigger, there may be more than one idler pulley.  The idler function is to stabilize areas of the drive that tend to create unwanted vibrations 

The tensioner ensures the correct and necessary tension of the timing chain that surrounds the crankshaft sprocket and the camshaft sprocket, making the chain run smoothly, preventing it from rattling and coming off the sprockets. 

A crankshaft pulley is a grooved wheel-shaped gadget that connects directly to the crankshaft of a vehicle. The crankshaft pulley essentially converts the linear or direct motion of the pistons into rotary motion.  Crankshafts are responsible for driving the wheels of the car.  

The water pump is designed as a cooling system component in charge of preventing the engine from overheating, and in most engines, it is driven by the timing belt and it derives its power from the crankshaft of the engine. 


Most vehicles, up until late 2000’s only function with a timing belt. It was typically less expensive, but has higher maintenance issues. With time, a timing belt can get worn and therefor needs to be replaced as often as 120 000km. Some manufactures prefer it to be earlier. When a timing belt does not get replaced, it will eventually snap (break) and cause a lot of damage to other engine components.

Timing belt diagram

What happens when a timing belt breaks?

A broken timing belt means that the valves do not have the necessary time to close before the piston arrives. Because of this, a collision will occur between the pistons and the valves. This collision causes the valves to bend.
From the moment the timing belt breaks, the camshafts stop immediately, under the action of return springs that slow down its cams.
The crankshaft, at this moment, inertially continues to rotate (regardless of whether the transmission was switched on or not, the speed was low or high, the flywheel continues to turn it). Thus, the pistons continue to work, and as a result, they will hit the currently open valves. Considering the valves, modern engines are much sensitive regarding this problem because of the small distance between the valves and the pistons. So, if the valve is slightly open when the piston arrives, it instantly bends.

Reasons why a timing belt would snap:

-A most common cause is a bad or failing water pump.
– A worn belt.
– Possible damages to the crankshaft.
– The belt loosens or tightens because the tension rollers are unscrewed.

Damaged exhaust & intake valves

Symptoms of a worn/bad timing belt

While you may not pay close attention to your vehicle’s timing belt, there are a few symptoms that might indicate that the belt needs urgent replacement.

A Ticking noise coming from the engine

If you hear a ticking noise coming from your car’s engine, this might indicate that the timing belt pulleys (which goes into the crankshaft) are worn or faulty.


Your car’s engine won’t turn over

When referring to an engine that won’t turn over, it simply means the vehicle won’t start at all. When your car’s timing belt is broken or irreplaceable, your engine will not be able to ignite or turn over properly. This means when you turn the key, you may hear the starter motor engage, but since the timing belt is responsible for operating the crank and shaft, it will not fully ignite. When your timing belt is broken, you won’t be able to drive your car at all.

You notice an oil leak near the motor

Another common symptom that indicates a bad timing belt, might be a visible oil leak coming from near the motor, which often occurs from the timing belt cover. While your timing belt cover may be secured by a series of nuts and bolts, it is very likely that they can come loose over time. This can lead to your engine overheating and other expensive repairs.

Oil leak or drop from engine of car on concrete floor , check and maintenance auto service

Exhaust issues

A lot of exhaust smoke also indicates a bad timing belt. Because the timing belt is already worn, your vehicle’s engine is now working a lot harder to perform. This excess work causes the vehicle to expel more exhaust gasses than it should.

High revs

The timing belt has a teeth-like appearance and when it gets worn, the teeth become smaller, until the belt is smooth on both sides. This may cause revs to be higher than usual because the timing belt has difficulty in rotating without grip.

A timing chain is one of the integral components of an internal combustion engine, without which efficient vehicle operations are impossible. Its failure can result in extensive engine damage costing the owner a fortune in repairs.

Car tachometer in 3d view.

Timing Chains

With technology improvements, timing chains were developed to make life a bit easier. Timing chains has a longer duration than timing belts and almost never need replacement There are companies that also expect their timing chains to last an entire lifetime on the vehicles. Timing chains are located on the inside of an engine and therefore are lubricated by the engine oil.


Composed of metal links, a timing chain runs along a set of gears to rotate the crankshaft and camshaft and regulates the opening and closing of the engine valves in coordination with the firing pistons. Since the timing chain is housed inside the engine, it receives its lubrication from the engine oil, which is essential for its smooth functions. Despite having a metallic composition, timing chains can wear off, stretch, get loose, or break due to stress.

Timing chain diagram

Symptoms of a stretched/bad timing chain

Like mentioned before, a timing chain is not a high maintenance component and therefor people tend to neglect it when doing overall maintenance on a vehicle. Although it is supposed to be a “life time” component, it can still get loose, damaged or stretched. Here are the symptoms of a bad timing chain:

Misfiring engine

Since the timing chain times the opening and closing of engine valves, any damage can unbalance the air-fuel ratio and result in a lack of power. It appears as a jerking motion and loss of acceleration, what we call a misfire.


Contaminated engine oil

As the timing chain gets worn, metal bits Another warning sign is finding metal bits in the engine oil. Contaminated engine oil might cause damage to other components as well, like the oil filter.

Engine warning light

Just like most malfunctioning engine component, a faulty timing chain will cause the ‘check engine’ light to appear on the dashboard. A lot of drivers tend to ignore these warning signs, unaware of the consequences it might have when it is not getting attention immediately.


Vehicle does not start

This is a sign of the ultimate breakage of the timing chain. The vehicle won’t start and can result in damaging other engine components as well.

No matter if your vehicle has a timing belt or chain, a regular inspection is necessary. Book your vehicle for an inspection at VAG Spec Centre and trust the specialists to take care of your vehicle and prevent bigger damage.