• Sat. Jun 22nd, 2024

The flywheel




Why Are Flywheels Important And What Different Types Are There?

The flywheel is in the form of a cast iron disc weighing between 5 and 10 kg. It is embellished with a toothed hoop all around.

Also called flywheel, it is connected on one side to the engine and on the other to the clutch. Thus, it is placed at the engine output, at the end of the gearbox shaft. It is attached to the crankshaft and therefore integral with the rotary movement of the engine.

The flywheel performs several functions within your car. It participates in the starting, clutch, transmission and damping of shocks and vibrations related to the rotation of the engine.


When starting, movement applied to the ignition key triggers the solenoid, an electromagnet that is part of the starter and acts as a switch. The solenoid in turn will act on the pinion of the starter, which will place itself “in gear” on the toothed circumference of the flywheel.

At the same time, the starter motor turns on and causes the pinion to rotate. This drives the flywheel, which then drives the crankshaft. It is this sequence that allows the engine to start.

switch on the ignition When the engine has started, the starter motor stops and the pinion separates from the flywheel. Note that stopping the starter is very important to prevent it from being damaged. Indeed, if it continues to rotate when the motor is already running, its rotation speed will be much too high.

Also, the starter motor is supplied with electricity coming directly from the vehicle battery. It is very power hungry and could quickly drain the battery if it continued to run.


The flywheel is directly linked to the clutch system. When you release your clutch pedal, the clutch disc comes to stick against the flywheel. The clutch disc is covered with a friction lining very similar to that which covers the brake pads. This composition allows it to adhere more easily to the flywheel.

Once the two discs are joined, the flywheel transmits the rotary motion of the engine to the clutch disc and the gearbox, which then send this energy towards the wheels.


As we have just seen, the flywheel is an essential part of the transmission, since it allows the rotational movement of the engine to be directed towards the clutch, which will in turn transmit it to the drive wheels.
Shock and vibration damping

As we explain to you in our article on the different types of engine, the engine of a thermal car works in cycles. Consequently, the rotations of the motor are not fluid: they are subject to jolts and vibrations.

Thanks to its considerable weight, the flywheel makes it possible to reduce the speed of the rotary movement, in particular at start-up, but also to regulate this speed by erasing its irregularities and jerks.

In concrete terms, this means that without the flywheel, our automobile would start and accelerate much too quickly. Also, the slowdowns would be much more abrupt and the car would inevitably end up stalling.

The dual-mass flywheel

Over time, as vehicles grew in horsepower, manufacturers were forced to make modifications to the classic flywheel. This is particularly the case with diesel cars. Indeed, the diesel engine delivers more torque than a gasoline engine. It is therefore noisier and more subject to vibrations.

Born in the 2000s, the dual-mass flywheel was introduced by manufacturers to obtain better driving comfort. For the reasons mentioned above, it is mainly found on diesel cars.

The dual-mass flywheel consists of two masses, one attached to the crankshaft and the other to the transmission. These two masses are interconnected by springs, cleats and a ball bearing. This device makes it possible to reinforce the damping of vibrations and jolts caused by the energy variations of the rotation cycles of the motor.

Flywheel maintenance

The flywheel is a fairly fragile part that should not be overlooked, especially the dual mass. If it has made it possible to significantly improve driving comfort, it is unfortunately quite unreliable. As it is a highly stressed part, the springs tend to wear out. After a while, they may break.

The flywheel being directly linked to the clutch, the slightest malfunction can have serious consequences on it. As a general rule, the replacement of the dual-mass flywheel is accompanied by a replacement of the clutch. It is therefore much more expensive than replacing a conventional flywheel.

The deterioration of a conventional flywheel can have two causes, which are also observable in the case of a dual-mass flywheel:  Clutch wear, which is not necessarily a defect. It is indeed the same principle as the brake pads. The friction lining that surrounds the clutch disc naturally hollows out as the clutch is stressed.

If the flywheel comes into contact with the abrasive clutch disc, this can cause serious damage. Rough driving can also promote flywheel wear. This is also the case for many parts of your car.

Signs of flywheel failure

It is not always easy to spot a malfunctioning flywheel, because the signs are the same as when it comes to a clutch problem:

You feel strong vibrations at the level of the clutch pedal;
Shifting is difficult, especially at low revs;
A clicking noise is heard from the engine when you engage the gear.

How to maintain the flywheel

First of all, it is very important to properly maintain your clutch system following the recommendations of your manufacturer, in order to prevent wear of it from causing damage to the flywheel.

If you notice any of the signs we have just seen, have your flywheel checked by your mechanic. Depending on the type of breakdown, it will be necessary to consider either having the part replaced, or correcting its surface by performing machining.

The starter pinion may be the cause of degradation of the toothed ring. If only this part is worn, it can be changed without having to replace the entire mechanism.

As a general rule, the life of a flywheel can be up to 200,000 km. If your flywheel breaks down before reaching 100,000 km, its replacement may be entirely or partly the responsibility of the manufacturer. But be careful, it also depends on your manufacturer’s warranty.

If it is still valid, you will have to contact your dealer, but you will not have to do anything with the manufacturer. On the other hand, if your guarantee is no longer valid, you will have to take the steps yourself with the manufacturer so that he can take charge of the replacement.

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