Reply to "Flywheel question."

Flywheel Inspection

If the ring gear is chewed-up then it will need replacement. If the flywheel’s clutch surface is flat but has the typical grooves and ridges, and can be cleaned up by removal of no more than 0.045” material, then a simple resurfacing may suffice, especially if the motor will only be used in a typical transportation application.

By my calculation 0.5mm is equivalent to 0.02", so the amount of material your mechanic feels is necessary to remove is within tolerance, its about 44% of what is allowable.

However, if the flywheel shows signs of stress cracking or heat checking, if it would require the removal of more than 0.045” material to clean it up, if it is warped or has excessive run-out, then the flywheel shall need to be replaced. A high mileage flywheel should be replaced if it shall be mated to a motor with increased output or installed in a car that shall be driven vigorously because a 40 year old cast iron flywheel should not be trusted to endure higher power output or vigorous usage.

The OEM flywheel is manufactured from cast iron, which is fine for typical transportation applications. However, a better choice for high performance applications is a lightened steel flywheel, which shall be tougher than the OEM cast iron flywheel, and the lighter weight will give the motor a little more pep too. At 26.4 pounds the Yella Terra #YT9902 is lightest steel flywheel known to me. Although an aluminum flywheel would be even lighter, the durability of the steel flywheel is more important than the light weight of an aluminum flywheel for a street car or sports car application. The Yella Terra flywheel is made of billet steel, it is designed for 11 inch clutches, it has a 164 tooth ring gear, and it is SFI approved. It is drilled for long style pressure plates identical to the OEM factory pressure plate, this is a durable and trouble free type of clutch. The flywheel is also configured for external balance applications (28 oz. imbalance).