Since both flywheel assemblies and flexplate assemblies accomplish the same function and are somewhat similar in appearance, they are often referred to interchangeably, but are in fact two different parts.
A flywheel gear is used primarily in manual transmissions. It is attached to the engine crankshaft, and holds the ring-gear that is used to crank the engine. The wheel connects directly to the clutch, stores energy to move the vehicle from inertia, and provides a friction surface for the clutch to attach to. Because of this, these parts are usually cast, and are thick and heavy, to allow for the clutch’s surface.
In addition, the heavy weight allows for more inertia once it is spinning.
These parts are manufactured through a casting method, and for now, sand casting is the most common production process for these OEM parts. Depending on the application, the materials used are nodular iron, steel or aluminum. Once cast, the wheel is finished by machining and boring.
Next, a square or rectangular steel bar of a preset length is bent into a circle configuration and the ends welded together, with the major diameter larger than the finished gear size.
The ring is then heated, and either stamped or bored to size on the minor diameter. Next, the gear teeth are hobbed onto the ring, and hardened to improve strength and resistance. Lastly, the ring is shrunk onto the flywheel.
When the engine is started, the engine crankshaft turns, and its pinion gear engages with the gear ring of the flywheel assembly to rotate it, in turn rotating the crankshaft on which it is mounted. The rotating crankshaft moves the engine parts through the combustion cycle to start the engine.
Once the engine is running on its own, the weighted and balanced disc of the wheel keeps the crankshaft running smoothly between combustion cycles, preventing the engine from slowing down between piston firings.
The Single Mass version was the original flywheel manufacturer design – later replaced by the popular Dual Mass design. This assembly was created for the high volume passenger car and light commercial vehicle market.
However, manufacturing experts say these complex multi-component units “have been plagued with reliability issues, often failing very early in their life expectancy”. Therefore, Single Mass version are ideal for high mileage vehicle applications.
The newer Dual Mass designs are commonly used in a manual transmission’s clutch assembly. This type of assembly helps cushion the shocks associated with the clutch release function. This fly-wheel has a performance feel during the clutch disengagement process and also helps prevent other parts from being damaged during operation vibration shocks.