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

S&S Cycle rear cylinder and piston kit for 2017+ Harley-Davidson Milwaukee-Eight engines, featuring a 4.250 in bore forged piston assembly. Designed to increase displacement and support higher compression builds on the M8 platform.

Features

• 4.250 in bore rear cylinder
• Forged piston assembly
• 2017+ Milwaukee-Eight (M8) compatibility

Specifications

• Brand: S&S Cycle
• Manufacturer Part #: 910-0737
• Bore Size: 4.250 in
• Position: Rear cylinder
• Engine: Harley Milwaukee-Eight (M8)
• Weight: 1 lb
• Category: Engine Components / Piston Sets - Powersports

Fitment

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

Frequently Asked Questions

Will this kit fit my Twin Cam Harley?

No — this kit is specific to Milwaukee-Eight (M8) engines only. Twin Cam owners need a different S&S Cycle piston kit.

What displacement increase does this bore provide?

The 4.250 in bore is designed for displacement increases on the M8 platform. Check S&S Cycle's displacement calculator for your specific engine configuration.

Is this a complete piston assembly or just the piston?

This is a rear cylinder and piston kit with forged piston assembly included.

Do I need to have my heads shaved or ported for installation?

Consult S&S Cycle technical support or your builder — compression and porting may be necessary depending on your specific build goals.