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

S&S Cycle big bore cylinder and piston kit for Harley-Davidson Milwaukee-Eight (M8) models with a 4.250 in. bore. Bolt-on design increases displacement and horsepower over stock M8 engines, finished in wrinkle black with highlighted cooling fins.

Features

• Bolt-on cylinder set for M8 engines
• 4.250 in. bore displacement increase
• Wrinkle black finish with highlighted fins
• Complete piston and ring package included

Specifications

• Brand: S&S Cycle
• Manufacturer Part #: 910-0682A
• Bore Size: 4.250 in.
• Finish: Wrinkle black with highlighted fins
• Weight: 29.56 lb
• Category: Engine Components / Piston Sets - Powersports

Fitment

Fits 2017 and newer Harley-Davidson Milwaukee-Eight (M8) models.

Frequently Asked Questions

What horsepower gain can I expect with this bore kit?

Horsepower varies by final displacement and tuning. Contact S&S Cycle or your dealer for dyno results on your specific model.

Do I need to retune my M8 engine after installation?

Yes — a fuel and ignition tune is strongly recommended to optimize performance and drivability with the larger displacement.

Is professional installation required?

This is an advanced engine modification. Professional installation by a Harley-certified tech is highly recommended to ensure proper assembly and tuning.

Will this kit void my warranty?

Engine modifications typically void the factory warranty. Check with your Harley dealer before installation.

What's included in the kit?

The cylinders, pistons, rings, and gaskets needed for installation. Hardware fasteners are included; verify all components before starting work.