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

S&S Cycle 114 to 128 cubic-inch big bore kit for 2017+ Harley-Davidson M8 engines, featuring forged pistons with 11:1 compression ratio and all gaskets and hardware needed for bolt-on installation. For closed-course competition use only.

Features

• 114 to 128 cu. in. displacement range
• Forged pistons with 11:1 compression ratio
• 4.250 in. bore x 4.5 in. stroke
• Bolt-on installation — no machining required
• Includes all gaskets and mounting hardware
• Highlighted cooling fins
• Wrinkle black finish

Specifications

• Brand: S&S Cycle
• Manufacturer Part #: 910-0684A
• Displacement Range: 114 to 128 cubic inches
• Bore: 4.250 in.
• Stroke: 4.5 in.
• Compression Ratio: 11:1
• Weight: 30.8 lb
• Category: Engine Components / Piston Sets - Powersports

Fitment

Fits 2017 and newer Harley-Davidson M8 engine models. For closed-course competition use only.

Frequently Asked Questions

Does this require engine machining or head work?

No — this is a bolt-on big bore kit. No machine shop work required for installation.

What's the compression ratio?

11:1 compression ratio, suitable for 91-octane fuel in competition engines.

Is this street legal?

No — S&S Cycle specifies this kit for closed-course competition use only. Not legal for street riding.

Does it come with gaskets and hardware?

Yes — all gaskets, seals, and mounting hardware needed for installation are included.

What M8 models will this fit?

Fits 2017 and newer Harley-Davidson models with the Milwaukee-Eight engine platform.