Why Do Timing Belts Have Teeth and How Do They Work?

Why do timing belts have teeth and how do they work?
Experienced mechanics share their insights in answering this question :
Timing belts have teeth for a frictional contact point to the sprockets, which have teeth to match with the belt. The sprockets are located on the engine crankshaft and camshaft. The timing belt is rotated by the engine’s crankshaft which transfer the movement to a camshaft or shafts (model dependent) to open the valves in the cylinder head, in order to control the air/fuel mixture into the engine cylinder. There is a timing sequence that happens with the pistons and valves to make engine power. This belt keeps that relationship accurate. The timing belt can also rotate a coolant pump. There is a service requirement for the timing belt. When service is required on the belt, the coolant pump should be replaced also.

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Our sources include academic articles, blog posts, and personal essays from experienced mechanics :

Timing belt pulley drive systems use teeth and grooves like a chain and sprocket to lock the drive and driven pulley together. These systems keep alignment by maintaining the engagement of precise teeth and pockets between the belt and pulley.
A toothed belt; timing belt; cogged belt; cog belt; or synchronous belt is a flexible belt with teeth moulded onto its inner surface. Toothed belts are usually designed to run over matching toothed pulleys or sprockets.
A timing belt is made of rubber with hard teeth capable of interlocking with camshafts and crankshafts cogwheels. It is an integral component of an internal combustion engine responsible for synchronizing the rotation of the camshaft and the crankshaft.
The timing belt is a rubber belt with hard teeth that interlock with the cogwheels of the crankshaft and the camshafts. It synchronizes the movement of the crankshaft and camshafts. This ensures that the engine intake and exhaust valves open and close in time with the pistons.
A toothed belt is a positive transfer belt that does not need friction for power transfer. It transfers force via teeth similar to chain or gear drives but with much lower noise levels and without the need for excessive lubrication.
In order to deliver the rated horsepower, a belt must have six or more teeth in mesh with the grooves of the smaller pulley.
A timing belt is a non-slipping mechanical drive belt and the term may refer to either: Toothed belt, a flexible belt with teeth moulded onto its inner surface. Timing belt (camshaft), a toothed belt used to drive the camshaft(s) within an internal combustion engine (a specific application of a toothed belt)
When the timing belt breaks, the crankshaft will continue to spin, while the camshaft will stop turning. As a result, the pistons will continue to rise and fall in their cylinders and can, in some instances strike the valves.
To make a timing belt, rubber is reinforced with corded fibers and then toothed to reduce friction and noise. Materials are molded into a premade shape and then the sleeve is precisely trimmed according to the requirements. Sometimes additional coatings are added for situations that require low dust.
Synchronous belts (also called cogged, timing, positive-drive, or high-torque drive belts) are toothed and require the installation of mating grooved sprockets. These belts operate with a consistent efficiency of 98% and maintain their efficiency over a wide load range.
Advantages of timing belt drive

No slipping between the belt and pulleys. Power transmission at a constant speed. Virtually no creep. Low noise and vibration.

In many cases a jumped timing belt will cause some engine damage. A timing belt can also strip teeth off, shred, or break entirely. On an interference engine this will cause engine components such as valves and pistons to collide which is every bit as bad as it sounds.
Lower maintenance requirements

A high quality belt will continue to transmit power for many years with minimal maintenance required. It will not rust, and is much more resistant to environmental contamination than chain.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

Timing belt is tight and yet appears to be slipping several teeth when belt is rotated,
ANSWER : This is okay since there are more notches on the belt than the amount on the sprockets. Once you aligned the first time the belt marks will almost never line up perfectly again. The marks are used to put the belt on correctly. They aren’t used as an indicator after the engine is turned again. You should be okay to start the motor as long as timing marks on pulleys line up. If you run into any issues, have a certified technician, like one from YourMechanic, assist you with the replacement of the timing belt.

When I went to change the timing belt there were 25 teeth were missing but it didn’t jump time – how is this possible?
ANSWER : Not all the teeth need to be present in order for the pulleys to turn. However, the only way to tell if the cam and crankshaft were really in the right position relative to one another is to line them up before taking the belt off and when the engine is at TDC on cylinder 1. If all the pulleys were lined up to the marks that are embossed on the engine, the only explanation is that the few remaining teeth were stout enough to turn the pulleys without breaking. However, even that doesn’t seem likely, especially since 25 missing teeth in a row would suggest that there weren’t even enough teeth for the belt to fully engage the crankshaft timing gear, thus slippage would have been inevitable. If the 2.0L engine you have has a double overhead cam, that is an interference engine (the single cam version of the 2.0L is a non-interference engine). If you’d like a professional technician check out the engine for damage, due to the failed belt, and/or install the new timing belt, consider YourMechanic.

hi- i got an estimate to replace my timing belt and water pump for my 2012 pilot. Do these figures seem right? Timing belt (35.00)
ANSWER : Hi there. That is a fairly good and detailed estimate for this type of service. It also falls within the price estimation to have a mechanic shop complete this service. However, you might want to consider a third option, of having a professional mobile mechanic come to your location and complete the timing belt replacement and water pump replacement. Simply click the blue links to receive an estimate for both services.

1992 Acura Legend, when the timing belt goes, is it common for the valves to bend?
ANSWER : If the timing belt break off, the engine’s pistons will hit the valves as the pistons are moving. The engine is an interference engine and can cause damage to the internals of the engine. The last time the belt came off, the engine may have been running at an idle or not under power. It is possible for the valves to be bent. What I recommend doing is performing a leak down test on the engine with a timing belt on the engine and properly timed to determine if the valves were in fact bent. If all of the cylinders have a 80 percent hold and not leaking, then the engine is fine. If there is a mass leak on a cylinder, then the piston did some internal damage. I recommend seeking out a professional, such as one from Your Mechanic, to help you check your engine’s valve train with a leak down tester.


Billing and parts question was sent to CS for the cost of parts and labor for valve train and related parts from a broken timing belt for a 1992 Acura Legend with a V6-3.2L engine.

timing belt and driving belt replacement interval
ANSWER : The timing belt should be checked every 24 months or 30K miles and replaced every 48 months or 60k miles. You are not due until 173k for a timing belt replacement, but should get inspected at 143k. The accessory belts should be inspected at every oil change and replaced as needed.

hey i had a belt break while traveling on my 2004 honda pilot. It is the small belt and not the serpentine belt. The mechanic t
ANSWER : Hello. The smaller belt is known as your timing belt, and it works inside the engine to keep mechanical components aligned with each other during the compression cycle. The serpentine belt, which is the big belt, drives the alternator, water pump, AC compressor, and a couple of other components. If the small belt broke it is likely the timing belt. This will cause the car to stall, lights to illuminate, and can even cause serious damage to the engine. Typically replacing a timing belt is a lot more complicated and expensive than replacing a serpentine belt. You may want to receive a second opinion on the car before you go ahead with repairs.

Timing Belt Cover replacement and External Belt too.
ANSWER : The parts are touching likely because either the parts were not installed properly or fasteners may be missing or broken. If oil has been leaking, this can cause the seal around the covers to swell as well causing misalignment. Consider hiring an experienced technician like one from YourMechanic who can come out and take a closer inspection of the belt drive to see what is causing the misalignment and offer a more personal diagnosis as well as estimate the proper repairs.

Serpentine belt tearing apart by pebble & pieces of it getting inside timing belt, motor destroyed
ANSWER : Hi there. I agree with you – this doesn’t pass the ’smell test’. The only way for debris to enter the engine is through the throttle body. Since the throttle body inlet is protected and covered by an air intake on your Ford Fiesta, I highly doubt that this is the source of your problems.