What Does A Timing Belt Do? (Function and Importance)

A timing belt ensures the synchronized rotation of the camshaft and crankshaft so that the valves open and close at the correct time in relation to the pistons. It also ensures proper circulation of the coolant by driving the water pump. When the timing belt fails to function properly, your car will face rough idling, excess emission, engine overheating, and even severe engine damage. 

There is no quick explanation for the question of what does a timing belt do. To know the purpose of a timing belt and why you need to maintain it carefully, read this article. 

What Does A Timing Belt Do? (Function and Importance)

Timing Belt: Definition And Diagram

Before understanding the timing belt’s function, it’s important to know what is a timing belt in a car and its surrounding components.

The timing belt is a flexible toothed belt, typically made with rubber or polyurethane with other reinforced materials. 

It synchronizes the rotation of the camshaft and crankshaft in an internal combustion engine. It makes sure the inlet and outlet valves open and close at the correct times in relation to the piston movement. 

What Components Are Connected To The Timing Belt?

The timing belt is connected to the following components in an engine.


The crankshaft is connected to the timing belt with the crankshaft pulley or gear. The teeth of the crankshaft gear are attached to the teeth of the timing belt. And the crankshaft pulley is connected to the engine pistons with a connecting rod.


The camshaft is connected to the timing belt via the camshaft pulley(s). And it is connected to the inlet and outlet valves via a system of rocker arms, pushrods, and lifters. Camshafts are responsible for the movement of these valves. 

There can be multiple camshafts connecting to the timing belt depending on the engine type. 

Source: Wapcar

Tensioner Pulley

The tensioner pulley ensures that the timing belt is properly tensioned and has a proper connection with all the other components.

Water Pump

In some engines, the water pump is driven directly by the crankshaft. But in most engines, it is driven by the timing belt.

If the water pump is driven by the timing belt, it will have a pulley that is connected to the pump by a shaft. 

What Does A Timing Belt Do On A Car?

The primary function of a timing belt is synchronizing the rotation of the camshaft and the crankshaft. 

When the engine starts, there is combustion of air and fuel in the engine cylinder that moves the pistons. The crankshaft converts this up-and-down movement from the engine’s piston to rotational motion. It helps initialize the rotation of the timing belt.  

The timing belt, in turn, rotates the camshaft pulley(s). The camshaft transforms this rotational motion into a reciprocating motion. It controls the opening and closing of the inlet and outlet valves. 

Timing Belt

The inlet valve allows fuel to enter the engine. And the outlet valve is responsible for expelling exhaust gasses from the engine. Together these two valves ensure the untroubled flow of an air/fuel mixture into the engine (1)

Source: Professional Automotive Repair

For efficient engine performance, this synchronization of the valves and pistons is crucial. To keep this process synchronized, there are specific ratios for camshaft and crankshaft rotation in different engines. For example – 

Engine TypeCamshaft: Crankshaft rotation ratio
Two-stroke engine1:1
Four-stroke engine1:2
Six-Stroke Engine1:3

Timing belts ensure proper rotation ratios between the camshaft and crankshaft. 

In most modern engines, a timing belt is also responsible for running the water pump. The timing belt runs over the water pump pulley, and the rotation of the belt in turns, runs the water pump. Finally, as the pump runs, it circulates the coolant through the engine to maintain optimum engine temperature.


The timing belt ensures the proper rotation timing of the crankshaft, camshaft, and water pump pulleys. 

What Happens When a Timing Belt Fails?

When the timing belt fails, it won’t be able to synchronize the rotation of the camshaft and crankshaft of the engine. The engine timing will be off, and as a result, the engine will stop operating.

If your car has a non-interference engine, it won’t face any further damage. Replacing the timing belt will be enough. This is because a non-interference engine has a gap between the piston and the valve which prevents them from colliding when the belt fails. 

However, in an interference engine, there is no gap between the piston and valves. So even a little mismatch in their movement timing can cause them to collide with each other.

So, if your car has an interference engine, the engine will be severely damaged when the timing belt fails. 

Signs That The Timing Belt Is Going Bad

A damaged timing belt might show some symptoms before it completely fails. Here are these symptoms. 

  1. Your car’s check engine light will be on.
  2. You will notice an abnormal fluctuation in the RPM, and your car will idle roughly.
  3. If the timing belt is failing, it may cause the engine to misfire or run poorly.
  4. The engine will overheat. 
  5. You will notice an excessive amount of emissions. 

So, whenever you notice these symptoms, check the timing belt and other components around it.

Here are some common reasons that can cause the timing belt to fail. 

  1. The belt is worn out or torn. 
  2. The belt’s teeth are missing or broken.
  3. The belt slipped from the pulley due to oil. 
  4. The belt is not correctly tensioned and aligned. 
  5. The belt has accumulated debris which is hampering smooth rotation. 
  6. The pulley bearing, water pump pulley, or camshaft sprocket is damaged. 
  7. The valve’s sealant or gaskets has been damaged, and oil is leaking. 

Identify and fix the problem immediately to ensure proper timing belt operation. Also, replace the timing belt after the manufacturer’s recommended interval (2). 

Timing Belt Vs. Timing Chain Vs. Timing Gear

In many cars, there are either timing chains or timing gears used instead of a timing belt. Although they are used for similar purposes, there are some dissimilarities among them.

Speaking of ‘differences’, here you’ll find what makes serpentine belts different from timing belts (in case, you’d like to know).

And, let’s get back to the point and explore the differences between timing belts, timing chains, and timing gear.

FeatureTiming BeltTiming ChainTiming Gear
Material It is made with rubber or polyurethane and reinforced with other materials for durability, like corded fibers. It is made with metals like steel or alloy. Timing gears are made of steel or aluminum. 
Controlled componentsCamshaft, Water pump (in some engines)Camshaft Camshaft
Risk of failureHighModerate to lowLow
Consequences of failureNon-interference engine will stop.The interference engine will be damaged. All types of engines will be damaged. All types of engines will be damaged. 
DurabilityIt has low to moderate durability depending on the belt quality and engine. It has moderate to high durability. It has high durability.
NoiseA well-conditioned timing belt doesn’t make noise.It makes moderate noise, especially during cold startup. A timing gear can make moderate metallic noise, especially due to lacking lubricant. 
Average LifespanThe average lifespan of the timing belt is 60,000 miles to 100,000 miles of driving, depending on the car model, driving condition, engine type, etc. A timing chain can last as long as the engine’s lifetime, depending on the car mode, driving pattern, and engine type. Timing gear lasts way longer than a timing belt. Usually, the engine’s lifetime.
Replacement costTiming belts are the least costly among the three. Depending on the quality, a timing belt kit (Includes: a timing belt, idler pulleys, and a tensioner) can cost from $100 to $350. And with labor costs, the total amount can be around $500 to $1000. A timing chain will cost from $90 and $800+, and with labor costs, the total amount can be around $1,600 and $1,800. A timing gear will cost at least $500. And the labor cost for replacing timing gear is also very high. 


The timing belt is less durable and requires more frequent replacement than the timing chain and timing gear. However, the timing belt is easier to replace and the replacement cost is also less than the other two options. 
What Does A Timing Belt Do_ (Function and Importance) Infographic


Can A Car Run Without A Timing Belt?

A car can not run without a timing belt as it synchronizes the camshaft and crankshaft rotation. Without the rotation of the camshaft, the inlet and outlet valves won’t open. This will block the intake air-fuel mixture and the exhaust. And without these, an engine can’t function. So, a well-conditioned and properly tensioned timing belt is essential for running a car. 

What Is The Difference Between A Timing Belt And A Serpentine Belt?

The timing belt synchronizes the proper rotation of the camshaft and crankshaft in the engine whereas, the serpentine belt drives engine accessories including the alternator, power steering pump and AC compressor. The timing belt has horizontal teeth to attach to the cam and crank pulley, in contrast, the serpentine belt has vertical grooves. 

What Are Timing Belts Made Of?

The timing belt is usually made of rubber, polyurethane, or neoprene. For ensuring the durability of the timing belt, fiberglass is used with rubber. And the teeth of a timing belt are covered in hard fabric. 


That was my take on what does a timing belt do. The timing belt is an essential part of the vehicle which is often neglected by car owners. To keep your engine efficiently running for a long time, you should take the maintenance of the timing belt seriously. 

Now it’s time for me to go. Have a nice day!

Written By

Photo of author

Aaron Byrne

Hi, Aaron Byrne here. I'm an expert automotive mechanic with 10 years of experience. I work on engine parts especially timing belts for their repair, maintenance, and replacement.

Fact Checked And Mechanically Reviewed By


Talha Atta

Talha Atta, a Mechanical Engineer and experienced technical content writer and editor at Autoglobes.com with a passion for the automotive industry.