A flywheel is a heavy wheel usually made of metal that is connected to an automobile’s drive shaft. It stores rotational energy, opposes changes in speed and helps stabilize shaft rotation. It is connected to the clutch, outlining one of its surfaces. Every time the clutch is replaced, it is recommended to check the flywheel to determine if it needs resurfacing or replacement.
To improve the life of a replacement clutch, the flywheel should be checked to ensure it has a smooth and flat surface. Evidence of warping, cracks or “hard spots” need to be inspected before the clutch is attached. If these defects are not found, then resurfacing is not necessary.
Hard spots are discolored and slightly elevated sections of the flywheel that can cause clutch chattering. Warping of the flywheel also causes chatter and vibrations and can be measured using a feeler gauge. Warpage measuring more than 0.002 inch per inch of flywheel diameter is recommended to be corrected by resurfacing; however, if a flywheel is found to have critical cracks, a replacement is already required.
Resurfacing is done either by grinding or cutting. Grinding uses a head and block machine or a dedicated grinder. The dedicated grinder can be used on different flywheel types such as flat and stepped flywheels, while the head and block grinder is usually used only for flat flywheels. Grinding can be done either by a wet process using silicone carbide stones, or by a dry process using cubic boron nitride (CBN) stones. Cutting is a less-preferred method because of its disadvantages, such as missing some hard spots or removing too much metal. With the cutting method, a brake lathe with cutting bits is used.
A dual mass flywheel (DMF) is essentially two rotating flywheels designed to counter higher torque generated by diesel engines. A DMF on some automobiles manufactured by BMW, General Motors and Porsche is not recommended to be resurfaced. The DMF of these automobiles need to be replaced if damaged. On the other hand, a DMF on Ford automobiles may be resurfaced by separating the two flywheels. After resurfacing, new bolts are recommended to be used to fasten the flywheels together.
