It is a large cylindrical gear that rotates directly with the movement of the crank connected to the crankshaft and provides the continuity of its movement by spending the power it receives at the ignition time for the rotation of the engine at other times. It provides the balance of the engine with the crankshaft.

In most models, the first movement required for the starting system is given by the starter and the flywheel. Its shape resembles a fan.

The materials are usually cast iron. Its faults are 'Kindness, Crack, Friction'. It can be repaired on a flywheel grinder if it has not exceeded the tolerance.

In energy and work machines, energy losses occur compulsorily due to construction and operating conditions, apart from mechanical losses such as friction, on the surfaces where motion and forces prevail.

In general, these energy losses, which occur more in turbo and reciprocating machines, can be greatly reduced by using flywheels. In reciprocating machines, although the operating conditions are completely smooth or the forces do not change, the flywheel is needed due to the imbalance on the basis of the construction of the parts.

The most important feature of the flywheel is that the energy to be lost can be stored in its body and it can be used when necessary. The geometric shape of a general flywheel should be a kind of cylindrical disk with a large diameter and a small width. The location of the flywheel in the system should be the one with the largest possible number of turns. If this place is not possible for some reason, it should be in the rotating place close to the highest speed. Under these conditions, the flywheel is in a state where it can gain the greatest energy in the system.