S&S Cycle 4.250-inch Bore Rear Cylinder & Forged Piston Kit - 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.
This S&S Cycle rear cylinder and piston kit is engineered for 2017 and newer Harley-Davidson Milwaukee-Eight engines, featuring a robust 4.250-inch bore and a durable forged piston assembly. Designed to significantly increase displacement, this kit supports higher compression builds and unlocks greater power on the M8 platform.
Why riders pick this
- 4.250-inch bore rear cylinder for increased displacement
- Includes a durable forged piston assembly
- Designed for 2017+ Milwaukee-Eight (M8) engines
- Supports higher compression performance builds
When you're pushing the limits of your Milwaukee-Eight, every component needs to perform. This S&S Cycle rear cylinder and forged piston kit is built for the demands of high-performance V-twins. The 4.250-inch bore provides the foundation for massive displacement gains, while the forged piston assembly ensures maximum strength and longevity under increased stress. It's a critical upgrade for any M8 owner seeking to build a truly potent engine.
Maximize Your Milwaukee-Eight's Power Output
- Features a 4.250-inch bore rear cylinder for substantial displacement
- Includes a high-strength forged piston assembly
- Specifically designed for 2017 and newer Milwaukee-Eight (M8) compatibility
- Supports higher compression builds for increased horsepower and torque
The Foundation for Serious M8 Performance
This rear cylinder and piston kit is an essential part of any serious Milwaukee-Eight performance build. The combination of increased bore and a robust forged piston allows your engine to breathe more freely and produce significantly more power. Pair it with the matching front cylinder and other S&S performance components to create a balanced, high-output M8 that delivers exhilarating performance every time you twist the throttle.
Specifications
- Brand: S&S Cycle
- Manufacturer Part #: 910-0737
- Bore Size: 4.250 in
- Position: Rear cylinder
- Engine: Harley Milwaukee-Eight (M8)
- Weight: 1 lb
- Category: Engine Components / Piston Sets - Powersports
Common questions
Will this kit fit my Twin Cam Harley-Davidson?
No, this S&S Cycle kit is specific to 2017 and newer Milwaukee-Eight (M8) engines only. Twin Cam owners will need a different S&S Cycle piston kit designed for their platform.
What displacement increase does this bore provide?
The 4.250-inch bore is designed to facilitate significant displacement increases on the M8 platform. Consult S&S Cycle's displacement calculator for your specific engine configuration and desired outcome.
Is this a complete piston assembly or just the piston?
This kit includes the rear cylinder and a forged piston assembly, providing a comprehensive upgrade for your Milwaukee-Eight's rear cylinder.
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 | Piston Sets - Powersports |
| SKU | T14-662022 |
| WEIGHT | 1.0 lb |