S&S 114"/117" to 128" Big Bore Kit for M8 Models

• S&S 114"/117" to 128" Big Bore cylinders
• Forged pistons
• Piston rings
• Wrist pins
• Circlips
• Required gaskets
• Required installation hardware

Converts 114" and 117" M8 Engines to 128"
Transforms compatible Harley-Davidson Milwaukee-Eight 114" and 117" engines with stock 4.500" stroke crankshafts into a 128 cubic inch high-performance setup.

Bolt-On Big Bore Kit
Designed as a bolt-on kit with no crankcase machining required, making it a more straightforward displacement upgrade.

4.250" Bore
Features a 4.250" bore to significantly increase displacement and support stronger engine performance.

Designed for Stock 4.500" Stroke Crankshafts
Engineered specifically for use with factory 4.500" stroke crankshafts found in 114" and 117" Milwaukee-Eight engines.

Updated Cylinder Design for Gen 1 & Gen 2 Compatibility
Features an updated cylinder design that allows fitment on both Gen 1 and Gen 2 Milwaukee-Eight models.

Forged Pistons Included
Includes forged pistons designed for strength, durability, and high-performance use.

11:1 Compression Ratio
Built with an 11:1 compression ratio to support increased horsepower, torque, and throttle response.

Works with Stock Crankcases
Designed to work with factory Milwaukee-Eight crankcases without machining.

Gaskets and Hardware Included
Comes with the required gaskets and hardware needed for installation.

Available in Highlighted or Non-Highlighted Finish
Choose wrinkle black with highlighted fins for a contrast-cut look or wrinkle black without highlighted fins for a more understated engine finish.

Built for High-Performance M8 Builds
A strong upgrade for riders looking to build a more powerful Milwaukee-Eight engine with increased displacement, torque, and horsepower potential.

Fits:

• Harley-Davidson 114" and 117" Milwaukee-Eight engines with stock 4.500" stroke crankshafts (Gen 1 & Gen 2 compatible)

Always confirm your exact year, model, engine size, crankshaft configuration, tuning setup, camshaft selection, exhaust, intake, and supporting components before ordering.

Important Notes:
For 114" and 117" M8 Engines with Stock Stroke Only
This kit is designed to convert compatible 114" and 117" Milwaukee-Eight engines equipped with stock 4.500" stroke crankshafts to 128". Confirm your engine size and crankshaft before ordering.

Professional Installation Required
Big bore kit installation requires advanced mechanical knowledge, proper tools, engine assembly procedures, and tuning. Professional installation is strongly recommended.

Tuning Required
Proper tuning is required after installation to ensure correct fueling, ignition timing, drivability, reliability, and maximum performance.

Supporting Components Recommended
For best results, supporting upgrades such as a performance camshaft, intake, exhaust, clutch, and proper tuning may be recommended based on your performance goals

What does the S&S 114"/117" to 128" Big Bore Kit do?
This kit converts compatible Harley-Davidson Milwaukee-Eight 114" and 117" engines with stock 4.500" stroke crankshafts to 128 cubic inches for increased displacement, horsepower, and torque.

What engines does this kit fit?
This kit is designed for Harley-Davidson 114" and 117" Milwaukee-Eight engines using stock 4.500" stroke crankshafts and is compatible with both Gen 1 and Gen 2 models.

Does this kit require crankcase machining?
No. This is a bolt-on big bore kit designed to work with stock crankcases.

What bore size does this kit use?
This kit uses a 4.250" bore.

What compression ratio is this kit?
The kit features an 11:1 compression ratio.

Are pistons included?
Yes. Forged pistons are included.

Does this kit include gaskets and hardware?
Yes. The kit includes the required gaskets and installation hardware.

What finish options are available?
This kit is available in wrinkle black with highlighted fins or wrinkle black without highlighted fins.

Will this increase horsepower and torque?
Yes. Increasing displacement from 114" or 117" to 128" can significantly improve horsepower and torque when paired with proper supporting components and tuning.

Is tuning required?
Yes. Proper tuning is required after installation.

Is professional installation recommended?
Yes. Professional installation is strongly recommended for proper engine assembly, clearances, torque specs, tuning, and long-term reliability.