S&S Cycle Flywheels — Harley-Davidson Street Glide, Softail Fat Boy 114, Road King Special (2017-2026)

S&S Cycle flywheels for Harley-Davidson, engineered with heat-treated 4140 material and balanced to support high-performance builds. Designed to handle higher RPM and power outputs while maintaining the precision machining that makes them the foundation of any competition engine.

Features

• Heat-treated 4140 steel — harder and more than twice as strong as stock
• S&S High Strength Connecting Rods designed with Finite Element Analysis
• Full-width wristpin connecting rods (requires S&S Performance Pistons)
• Capable of higher RPM and more available power
• Balanced for S&S Performance piston weight (1213g)
• Balance gear installed
• 4-3/8" stroke (107 or 124ci)
• Consistent balance and precision machining

Specifications

• Brand: S&S Cycle
• Manufacturer Part #: 320-0604
• Category: Drivetrain / Flywheels
• Weight: 40 lb
• Material: Heat-treated 4140 steel

Fitment

Fits Harley-Davidson models. Designed for Milwaukee-Eight platform engine builds.

Frequently Asked Questions

Do these flywheels require S&S Performance Pistons?

Yes — the full-width wristpin design requires S&S Performance Pistons for proper fit and function.

What stroke does this give me?

4-3/8" stroke, supporting 107 or 124 cubic inch displacement builds.

Are these balanced?

Yes — balanced to S&S Performance piston weight (1213g) and include the balance gear installed.

Can I use these with gear drive cams?

Yes — these flywheels are compatible with gear drive cam systems.

Are these stronger than stock flywheels?

Yes — heat-treated 4140 material is more than twice as strong as stock, and the design eliminates the need to weld the crankpin.