✓ VERIFIED
Sep 26, 2019
Really nice kit great directions for install and ring gap. Follow the directions and you can't go wrong..
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S&S CYCLE
SKU: T14-1026223
S&S Cycle 131" Big Bore Cylinder & Piston Kit - Harley Milwaukee-Eight
$2,695.95
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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.
The S&S Cycle 131 cubic inch cylinder and piston kit delivers a huge displacement increase for 2017-later Harley Milwaukee-Eight engines. It’s engineered to bolt directly into stock crankcases without any machine work, providing substantial horsepower and torque gains while maintaining the original engine appearance.
Why riders pick this
- Huge displacement increase for substantial power gains
- Bolts directly into stock crankcases without machining
- Retains original engine serial numbers and factory look
- Powder coat finish matches OEM engine components
- Includes 131" cam cover badge
Transform your Milwaukee-Eight into a true sleeper with the S&S Cycle 131" Big Bore Kit. This kit is designed for a straightforward installation, allowing you to achieve massive displacement and a corresponding power gain without the need for costly and time-consuming machine shop work on your crankcases. It's the ultimate way to get big-inch performance while retaining your original engine's serial numbers and factory look.
Massive Power, Seamless Integration
- Achieve 131 cubic inches of displacement for significant power gains
- Designed to bolt directly into stock Milwaukee-Eight crankcases
- Retains original engine serial numbers and factory height
- Powder coat finish matches OEM engine components
- Includes 131" cam cover badge for a custom touch
Sleeper Performance for Your M8
This S&S Cycle kit is all about maximizing your Milwaukee-Eight's potential with minimal fuss. By maintaining the stock engine height and appearance, your bike will look factory while secretly packing a serious punch under the hood. The kit includes everything needed for installation, ensuring a complete and professional upgrade. Get ready to experience a whole new level of performance from your Harley-Davidson Touring or Softail.
Specifications
- Brand: S&S Cycle
- Manufacturer Part #: 320-0621
- Displacement: 131 cubic inches
- Bore: 4.250"
- Stroke: 4.625"
- Compression Ratio: 11.0:1
- Weight: 70 lb
- Category: Engine Components / Piston Sets - Powersports
Common questions
Will this 131" kit fit my M8 engine without requiring any machine work?
Yes, this S&S Cycle kit is specifically designed to bolt directly into stock Milwaukee-Eight crankcases without any boring, honing, or other machining required.
Will this kit change the external appearance or height of my engine?
No, this kit is engineered to retain the stock engine height and appearance, allowing for a 'sleeper' build. It also includes a 131" cam cover badge if you wish to display the upgrade.
What is included with the 131" cylinder and piston kit?
The kit includes cylinders, pistons, rings, wristpins, and all necessary gaskets for installation, providing a complete package for your displacement upgrade.
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 | T14-1026223 |
| WEIGHT | 70.0 lb |
Please contact us to confirm fitment for your specific motorcycle, or check the product title for compatibility notes.
CUSTOMER REVIEWS
4.88
8 RATINGS
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✓ VERIFIED
Apr 26, 2022
Excellent service and pricing im very satisfied
✓ VERIFIED
Sep 26, 2019
Better than OEM.. can't go wrong.
✓ VERIFIED
Mar 30, 2026
Very happy with this kit
Simple, easy kit.
✓ VERIFIED
Mar 29, 2026
SMS makes great aftermarket upgrades
✓ VERIFIED
Oct 24, 2025
👍👍 For fast delivery
Parts came just like as expected. They look great! Can't wait to install these bad boys along with a few other parts.