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

S&S Cycle 4.25in bore x 4.5in stroke big bore cylinder and piston kit for 2017+ Harley-Davidson Milwaukee-Eight engines, rated 117–128 cubic inches. Forged pistons with 11:1 compression ratio bolt directly onto M8 blocks with no machine work required.

Features

• Forged pistons with 11:1 compression ratio
• 4.25in bore x 4.5in stroke
• Bolt-on installation — no machining required
• Includes gaskets and all mounting hardware
• Wrinkle black finish with highlighted fins
• For closed-course competition use only

Specifications

• Brand: S&S Cycle
• Manufacturer Part #: 910-0733A
• Bore x Stroke: 4.25in x 4.5in
• Displacement: 117–128 cubic inches
• Compression Ratio: 11:1
• Piston Type: Forged
• Finish: Wrinkle black
• Weight: 29.75 lb
• Category: Engine Components / Piston Sets - Powersports

Fitment

Fits 2017 and newer Harley-Davidson Milwaukee-Eight (M8) engines. For closed-course competition use only.

Frequently Asked Questions

Will this fit my 2017+ M8 Touring or Softail?

Yes — this kit fits all 2017+ Milwaukee-Eight engines. However, it is rated for closed-course competition only, not street use.

Do I need to have my cylinders machined?

No. This is a true bolt-on kit — no machine work or custom boring required. Gaskets and hardware are included.

What compression ratio do these pistons deliver?

11:1. This is a high-compression ratio designed for premium fuel and competition tuning.

What's the displacement after installation?

This kit displaces 117 to 128 cubic inches depending on final assembly and tuning.

Is this street legal?

No — S&S rates this kit for closed-course competition use only. It is not approved for street riding.