Flywheels are bolted to the engine crankshaft and serve as the mounting-surface of the clutch assembly, while also acting as a heat sink to dissipate heat from the pressure plate and disc. During engagement, the disc is clamped between the pressure plate and flywheel, resulting in power transfer from the engine to the transmission. Contact between the flywheel and disc will naturally cause hot spots, grooves, thermal cracks and/or frequent concave warpage. Therefore, the flywheel should always be replaced or resurfaced during each clutch system replacement. Keep in mind, some flywheels are virtually impossible to resurface. Equipment plays an important role in the quality of the flywheel surface. AMS does not recommend the use of brake rotor lathes or small tool room lathes. Hot spots are significantly harder than the surrounding flywheel material. Brake rotor and small tool room lathes do not have the required cutting capacity to allow the cutting tool to remove hot spots in a uniform manner. Instead, a flywheel grinder or CNC lathe should be used.
No specific guidelines exist regarding the maximum amount of metal that can be removed from the friction surface. Removing too much metal may result in a no-release condition, because the mounted position of the flywheel and clutch assembly has been moved away from the release mechanism (AMS does NOT suggest the use of shims). An over-machined flywheel may also destroy the heat sink capacity and create a safety hazard. Conversely, if hot spots and wear flaws are not removed, and the flywheel is not returned to like-new flat condition, power transfer and component life will be minimized by chatter, slipping, and heat build-up. Further complicating matters, many flywheels utilize either a recess or step configuration, in which flywheel mounting-surface is higher or lower than the actual wear surface. It is imperative to maintain the proper step or recess dimension. Before grinding, the pressure plate mounting-surface should be measured relative to an unworn portion of the wear surface. While it may be difficult to find these specifications in O.E.M. manuals, the proper dimensions can be double-checked in any AMS catalog.