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

S&S Cycle 131" displacement cylinder and piston kit for 2017-up Harley Milwaukee-Eight engines, designed to bolt directly into stock crankcases with no machine work or boring required. Delivers significant horsepower and torque gains while retaining the factory appearance of an unmodified engine.

Features

• 4.250" bore, 4.625" stroke displacement
• 11.0:1 compression ratio
• Works with stock crankcases and engine height
• Powder coat finish matches OEM finishes
• Includes all gaskets and hardware for installation
• 131" cam cover badge included
• Retains original engine serial numbers

Specifications

• Brand: S&S Cycle
• Manufacturer Part #: 320-0623
• 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

Do I need to have machine work done on my crankcase?

No — the kit bolts into stock crankcases without boring, honing, or any other machine work required.

Will this change my engine appearance?

No — the sleeper design keeps your bike looking stock externally. An optional 131" cam cover badge is included if you want to advertise the upgrade.

What compression ratio does this kit run?

11.0:1 compression, suitable for regular pump gas in most riding conditions.

What's included in the box?

Cylinders, pistons, all necessary gaskets, hardware, and the 131" cam cover badge.

Can I keep my original engine serial number?

Yes — the kit is engineered to retain your original engine serial numbers and casting marks.