✓ 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: T14-852164
S&S Cycle 4.320" Big Bore Cylinder & Piston Kit - Harley Milwaukee-Eight
$1,643.95
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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.
Unlock significant power gains for your Harley-Davidson Milwaukee-Eight engine with the S&S Cycle 4.320-inch big bore cylinder and piston kit. This kit transforms your 107-inch M8 to 129 inches or your 114-inch M8 to 132 inches, all without requiring crankcase machining.
Why riders pick this
- Upgrades 107" to 129" or 114" to 132" M8
- Works with stock crankcases, no machining
- 4.320-inch bore diameter for more displacement
- Retains stock engine height
- Powder coat finish matches factory look
- Includes MLS head gaskets and cam cover badge
The S&S Cycle 4.320-inch big bore cylinder and piston kit is engineered for riders seeking a massive displacement increase and substantial power gains from their Milwaukee-Eight. This innovative kit allows for a drop-in installation, eliminating the need for complex and costly crankcase machining. You get the benefit of a bigger engine and more power, all while maintaining the stock engine height and a factory-matching finish.
Effortless Power Increase
- Converts 107" M8 engines to 129" or 114" M8 engines to 132"
- Works with stock crankcases, requiring no machine work for installation
- Features a 4.320-inch bore diameter for increased displacement
- Retains stock engine height for a seamless fit
- Powder coat finish is designed to match the factory engine appearance
- Includes MLS (Multi-Layered Steel) head gaskets for a robust seal
A True Bolt-On Big Bore
This S&S Cycle kit is a game-changer for Milwaukee-Eight owners looking for a straightforward path to serious power. The design prioritizes ease of installation, allowing you to achieve massive displacement gains with minimal fuss. Along with the performance benefits, the kit includes a Cubic Inch Cam Cover Badge, letting you proudly display your engine's new capabilities. Remember to pair this big bore upgrade with a compatible cam and a professional dyno tune for optimal performance.
Specifications
- Brand: S&S Cycle
- Manufacturer Part #: 910-0843A
- Bore Diameter: 4.320 in
- Weight: 29.56 lb
- Category: Engine Components / Piston Sets - Powersports
- Country of Origin: USA
Common questions
Do I need to machine my crankcases for this S&S Cycle big bore kit?
No, this S&S Cycle kit is specifically designed to work with stock Harley-Davidson Milwaukee-Eight crankcases, requiring no machining for installation.
What displacement will my engine be after installing this kit?
If you have a 107" Milwaukee-Eight, it will become 129". If you have a 114" Milwaukee-Eight, it will be upgraded to 132".
Will this kit change my engine's external appearance or height?
No, this kit is designed to retain your stock engine height, and the powder coat finish is matched to blend seamlessly with your factory engine's appearance.
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 | T14-852164 |
| WEIGHT | 29.56 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.