Flywheel
A heavy metal disc attached to the crankshaft that stores rotational energy, smooths engine cycles, and mates with the clutch.
The flywheel is a large, heavy steel or cast iron disc bolted to the rear of the engine's crankshaft. It serves three critical purposes in the drivetrain: it stores rotational inertia to smooth out the power pulses of the pistons, provides a ring gear for the starter motor to engage and crank the engine, and serves as the primary mounting and friction surface for the clutch assembly in manual transmission vehicles.
Because internal combustion engines produce power in pulses (only during the power stroke of each cylinder), the flywheel's weight and inertia keep the crankshaft spinning smoothly between these pulses. In automatic transmission vehicles, the flywheel is replaced by a lighter **flexplate** which mounts the heavy torque converter.
Modern vehicles often use a **Dual-Mass Flywheel (DMF)**, which splits the flywheel into two sections connected by internal springs and dampening mechanisms. This design absorbs drivetrain vibrations and reduces gear rattle, but is more complex and expensive to replace.
Issues with flywheels include cracked or worn starter ring gear teeth, scoring or heat cracking on the friction surface (caused by a slipping clutch), and failure of the internal springs in dual-mass designs. Symptoms of a bad flywheel include grinding noises when starting, clutch chatter or vibration, and slipping gears.