What does a flywheel do?
The flywheel in your car sits between the engine and clutch, helping to make driving smooth and reduce stalling by balancing out the up and down motion of the engine’s pistons. If you don’t know how single-mass and dual-mass flywheels work, and what role they play in a car, Halfords can help. Our guide on how flywheels work will answer these questions (and more).
What is a flywheel?
The flywheel sits between the engine and the clutch in manual cars. It helps to smooth the connection between the engine and clutch.
The flywheel spins around, storing rotational energy. When you remove your foot from the accelerator, the rotational energy stored in the flywheel keeps the car moving or idling without the engine stalling.
Flywheels also work to smooth the transition of power from the clutch, making driving easier and travelling more comfortable.
There are two types of flywheels: single-mass flywheels and dual-mass flywheels.
What's the difference between a single-mass flywheel and a dual-mass flywheel?
Single-mass flywheels are thick metal discs made from iron, steel, or in some cases, aluminium. On the outside edge of the flywheel is a toothed ring gear that when engaged with the starter motor, starts the engine. The flywheel is connected directly to the crankshaft and contained within the bell housing of the gearbox. One side is machined flat, to provide a stable connecting surface for the clutch plate.
Many modern cars are fitted with dual-mass flywheels. Made from two flywheels, one is connected to the clutch and the other to the crankshaft. They're joined by a series of springs that act as mechanical dampeners, reducing damage that could be caused by engine vibrations.
What problems can happen with a flywheel?
Flywheels are heavy-duty car parts that should provide years of faithful service. However, leaks from the engine crankshaft seal or gearbox input shaft seal can allow unwanted oil onto the flywheel. This can cause clutch slippage, in turn generating excessive friction and heat, which can warp the flywheel and, in some cases, cause heat cracks. This can also be caused by a worn and slipping clutch.
As well as the potential for damage and warping, dual mass flywheels are complicated pieces of engineering with more moving parts that can fail.
Your flywheel should last between 80-100,000 miles but this can depend on your driving style, driving conditions and the condition of your car. Flywheels are fit-and-forget parts on most cars, but if your flywheel begins to fail there are some things to look out for.
How can I tell if my flywheel is damaged?
Some of the signs your flywheel may be damaged include:
- A clutch pedal that feels hard
- Problems changing gear
- Rattling noises from the engine
- A feeling like the car is jerking or shaking
- A slipping clutch can damage the flywheel
If your flywheel has warped or some of the ring gear teeth are worn or broken, you may experience problems starting the car as the starter motor can't engage properly.
When should I replace my flywheel?
Replacing a flywheel is pretty major surgery for your car and a job for a professional mechanic. If you're experiencing issues with your flywheel, gearbox, clutch, or having starting or running problems, then book an appointment at a Halfords Autocentre. Our trained technicians can diagnose the issue and provide a price to fix it.
The flywheel and clutch assembly work together, so must both be replaced at the same time to give your car many more years of safe and smooth driving.