S&S Cycle Flywheels 4-3/8 in. Stroke, Performance Piston Weight - Harley Milwaukee-Eight
About S&S Cycle
S&S Cycle has built American V-twin performance parts in Viola, Wisconsin since 1958 — flywheels, carburetors, cams, cylinder heads and complete crate engines. When a Harley owner talks about a 124, a 128 or a 131 build, they are usually talking about S&S. Few names carry more weight with engine builders in this space.
Build a high-performance Harley Milwaukee-Eight engine with S&S Cycle Flywheels, engineered to handle serious power and higher RPMs. Forged from heat-treated 4140 steel, these flywheels are the foundation for any competition-level V-twin. They're meticulously balanced and designed for optimal strength and precision.
Why riders pick this
- Heat-treated 4140 steel, over 2x stronger than stock
- Includes S&S High Strength Connecting Rods
- Requires S&S Performance Pistons
- Balanced for S&S Performance piston weight (1213g)
- 4-3/8 inch stroke for 107 or 124ci M8 builds
These S&S Cycle flywheels are designed for the rider who demands the absolute most from their Milwaukee-Eight engine. Utilizing heat-treated 4140 steel and S&S High Strength Connecting Rods, which are designed with Finite Element Analysis, they offer more than twice the strength of stock components. The full-width wristpin design is specifically engineered to pair with S&S Performance Pistons, creating an incredibly robust assembly capable of delivering more available power and handling higher RPMs consistently. This 4-3/8 inch stroke is ideal for 107 or 124 cubic inch M8 builds.
Unleash Your Milwaukee-Eight's Potential
- Forged from heat-treated 4140 steel for superior strength
- Features S&S High Strength Connecting Rods
- Full-width wristpin design requires S&S Performance Pistons
- Balanced for S&S Performance piston weight (1213g)
- Supports higher RPM and increased power output
- 4-3/8 inch stroke for 107 or 124 cubic inch M8 builds
The Heart of a Competition Engine
Installing these S&S Cycle flywheels is a significant step towards building a truly high-output Milwaukee-Eight engine. Their precision machining and consistent balance are crucial for maximizing performance and durability under demanding conditions. Due to the specialized full-width wristpin design, it's critical to pair these flywheels exclusively with S&S Performance Pistons. Always confirm compatibility with your specific engine displacement and build goals before making your selection.
Specifications
- Brand: S&S Cycle
- Manufacturer Part #: 320-0604
- Category: Drivetrain / Flywheels
- Weight: 40 lb
- Material: Heat-treated 4140 steel
Common questions
Do these flywheels require S&S Performance Pistons?
Yes, the full-width wristpin design of these S&S Cycle flywheels is specifically engineered to require S&S Performance Pistons for proper fitment and optimal operation.
What stroke length do these flywheels have?
These flywheels feature a 4-3/8 inch stroke, making them suitable for 107 or 124 cubic inch Milwaukee-Eight engine builds.
Are these designed for stock Milwaukee-Eight engines?
No, these flywheels are designed for high-performance builds and require S&S Performance Pistons, making them ideal for custom or competition M8 engines rather than stock replacements.
Ordering from Vtwinbikers
- Brand new, sourced through authorized US distribution — never used, never grey-market.
- Not sure it fits? Use Shop by Bike to filter by your year and model, or email us and we will confirm before you order.
- Harley-Davidson and Indian Motorcycle is all we do, so you are talking to people who ride what you ride.
| BRAND | S&S Cycle |
| TYPE | Flywheels |
| SKU | T14-662049 |
| WEIGHT | 40.0 lb |
