S&S Cycle 128 CI Big Bore Cylinder & 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.
Transform your 2017-later Harley-Davidson Milwaukee-Eight engine with the S&S Cycle 128 cubic-inch big bore kit. This setup is engineered for increased displacement and performance, making it a prime upgrade for closed-course competition.
Why riders pick this
- Boosts 114 CI M8 engines to 128 CI
- Forged pistons deliver 11:1 compression
- Bolt-on installation requires no machining
- Includes all gaskets and mounting hardware
- Wrinkle black finish with highlighted fins
- Designed for closed-course competition use
When you're chasing every last bit of power from your Milwaukee-Eight, the S&S Cycle 128 CI Big Bore Cylinder & Piston Kit delivers. This kit is designed to bump your M8 engine up to 128 cubic inches, providing a significant increase in displacement for a noticeable boost in power and torque. It's a comprehensive package built for riders who demand more from their V-twin.
Competition-Ready Performance
- Engineered to transform 114 cubic-inch M8 engines into 128 cubic inches
- Features forged pistons with an 11:1 compression ratio for high performance
- Designed for bolt-on installation, eliminating the need for crankcase machining
- Includes all necessary gaskets and hardware for a complete upgrade
- Wrinkle black finish with highlighted cooling fins for a factory-plus look
Unleash Your Milwaukee-Eight's Potential
This big bore kit is specifically developed for closed-course competition use, offering a direct path to higher performance. The forged pistons and increased displacement work together to unlock the full potential of your M8, whether you're building a performance bagger or a custom Softail. Pair this kit with a performance cam and a proper dyno tune to maximize your gains.
Specifications
- Brand: S&S Cycle
- Manufacturer Part #: 910-0684A
- Displacement Range: 114 to 128 cubic inches
- Bore: 4.250 in.
- Stroke: 4.5 in.
- Compression Ratio: 11:1
- Weight: 30.8 lb
- Category: Engine Components / Piston Sets - Powersports
Common questions
Does this big bore kit require machining of my engine cases?
No, this S&S Cycle 128 CI kit is designed for bolt-on installation and does not require any machining of your factory crankcases.
What kind of performance increase can I expect?
This kit significantly increases your Milwaukee-Eight engine's displacement to 128 cubic inches, which typically results in substantial gains in horsepower and torque. A custom dyno tune is recommended to optimize performance.
Is this kit suitable for street use?
No, this S&S Cycle big bore kit is explicitly rated and intended for closed-course competition use only.
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 | T14-852158 |
| WEIGHT | 30.8 lb |