This 4-1/4" stroke 8-1/2" diameter flywheel assembly replaces the original flywheels in S&S® 80" SH80 engines with alternator style crankcases for 1970-'84 HD® big twins. May also be used in 88" engines with 3-5/8" bore cylinders. Flywheels are CNC machined from heat-treated, closed die, steel forgings, and are stronger than cast iron or late style steel flywheels. Dynamically balanced and fully assembled with premium quaility S&S® mainshafts and heavy duty 7.440" connecting rods.