✓ 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: T14-852166
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.
Experience a significant power boost with the S&S Cycle 4.320-inch bore cylinder and piston kit for Milwaukee-Eight engines. This bolt-on big bore package requires no machine work to your factory crankcases, transforming a 107-inch M8 to 129 inches or a 114-inch M8 to 132 inches.
Why riders pick this
- Upgrades 107" to 129" or 114" to 132" M8
- 4.320-inch bore cylinder for big displacement
- Works with stock crankcases, no machining needed
- Includes MLS head gaskets
- Powder coat finish matches factory look
- Retains stock engine height
The S&S Cycle 4.320-inch big bore kit is the ultimate solution for Milwaukee-Eight riders seeking massive displacement and substantial power gains without the hassle of extensive engine modifications. This kit is engineered for a direct, slip-in installation, preserving your stock crankcases while significantly increasing your engine's cubic inches. Enjoy impressive horsepower and torque while maintaining the original engine bay profile.
Unleash More Power with Ease
- Transforms 107" M8 engines to 129" or 114" M8 engines to 132"
- Features a 4.320-inch bore cylinder for maximum displacement
- Works seamlessly with stock crankcases, eliminating machine work
- Includes MLS (Multi-Layered Steel) head gaskets for a reliable seal
- Powder coat finish is designed to match your factory engine appearance
- Retains stock engine height for a clean, integrated look
Maximize Your M8's Potential
This S&S Cycle big bore kit is a testament to straightforward performance upgrades. By providing a substantial displacement increase, it sets the stage for a truly high-performance V-twin. The inclusion of a Cubic Inch Cam Cover Badge lets you showcase your engine's new capabilities. For the best results, we recommend pairing this kit with a performance camshaft and a professional dyno tune to fully optimize your Milwaukee-Eight's newfound power.
Specifications
- Brand: S&S Cycle
- Manufacturer Part #: 910-0845A
- Bore: 4.320 inches
- Category: Engine Components / Piston Sets - Powersports
- Weight: 29.56 lbs
- Country of Origin: USA
Common questions
Do I need to have my crankcases machined for this big bore kit?
No, this S&S Cycle kit is designed as a slip-in big bore, meaning your stock crankcases require zero machine work for installation.
What will my engine's displacement be after installing this kit?
A 107" Milwaukee-Eight engine will become 129" after installation, and a 114" Milwaukee-Eight will be upgraded to 132".
Will this kit alter the external height of my engine?
No, this S&S Cycle kit is engineered to retain your stock engine height, ensuring a consistent profile in your engine bay.
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 | T14-852166 |
| 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.