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

S&S Cycle 4.320" bore cylinder and piston kit transforms a 107" M8 engine to 129" or a 114" to 132" with a bolt-on big-bore package that requires no machine work to factory crankcases. Massive displacement gain delivers significant horsepower and torque while keeping the engine bay profile stock.

Features

• 4.320" bore cylinder
• Works with stock crankcases — no machine work required
• MLS multi-layered steel head gaskets
• Powder coat finish matches factory
• Retains stock engine height
• Cubic Inch Cam Cover Badge included
• Made in USA

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

Fitment

Fits Harley-Davidson Milwaukee-Eight (M8) engines: 107" base displacement to 129", or 114" base displacement to 132".

Frequently Asked Questions

Do I need to have my crankcases machined?

No — this kit is designed as a slip-in big bore. Stock crankcases require zero machine work for installation.

What displacement will my engine be after installation?

A 107" M8 becomes 129"; a 114" M8 becomes 132". Your starting displacement determines your final size.

Will I need a tuner after installing this kit?

A fuel and ignition tune is strongly recommended to optimize power delivery with the larger displacement.

Does this affect engine height or width in the frame?

No — the kit retains stock engine height and profile, so it fits in the stock engine bay without modifications.

What's included in the kit?

Cylinder, piston, MLS head gaskets, hardware, and a Cubic Inch Cam Cover Badge. Refer to S&S installation documentation for additional items like rings and bearings if needed.