S&S Cycle Cylinder & Piston Kits — Harley-Davidson Street Glide, Softail Fat Boy 114, Road King Special (2017-2026)

S&S Cycle 131 cubic inch cylinder and piston kit for 2017+ Harley Milwaukee-Eight engines, engineered to bolt into stock crankcases without machine work. Gains substantial displacement and horsepower while maintaining the original engine appearance and serial numbers for a true sleeper build.

Features

• Huge displacement increase with corresponding power gain
• Original engine serial numbers retained
• Powder coat finish matches factory finishes
• Includes 131" cam cover badge
• Works with stock crankcases
• Retains stock engine height
• 4.250" bore, 4.625" stroke
• 11.0:1 compression ratio

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

Fitment

Fits Harley-Davidson Milwaukee-Eight (M8) engines, 2017 model year and newer.

Frequently Asked Questions

Will this kit fit my M8 engine without machine work?

Yes — the kit is designed to bolt directly into stock M8 crankcases with no boring, honing, or machining required.

Do I need to change my engine serial number or re-register my bike?

No — S&S retains your original engine serial numbers, so your registration and title remain unchanged.

What's included in the kit?

The cylinder and piston assembly, all necessary gaskets for installation, and a 131" cam cover badge if you want to display the upgrade.

Does this increase engine height or affect my current setup?

No — the kit retains stock engine height and works with your stock crankcase, so fitment remains the same as factory.

What kind of power gain can I expect?

Displacement increases from 107 to 131 cubic inches typically result in substantial horsepower and torque gains. Dyno results vary based on intake, exhaust, and tune.