S&S Cycle Engines — Harley-Davidson Softail Heritage Classic, Softail Fat Boy, Softail (1983-2026)

S&S Cycle MK136B is a 136-cubic-inch complete crate engine for 2018-2024 Harley-Davidson Softail models, built on billet MKB-Series crankcases with high-flow cylinder heads and premium valvetrain components. Race-only application, not street-legal.

Features

• 136 cubic inch displacement
• High-flow cylinder heads with premium seats and guides
• 1mm oversized intake and exhaust valves
• .605" max lift valve springs
• Valves .030" longer than stock
• Billet aluminum covers
• Sprocket shaft spacer included

Specifications

• Brand: S&S Cycle
• Manufacturer Part #: 310-1295
• Displacement: 136 cubic inches
• Weight: 135 lb
• Application: Race-only

Fitment

Fits 2018-2024 Harley-Davidson Softail models with M8 mounting points. Race-only; not intended for street use.

Frequently Asked Questions

Will this fit my 2017 or older Softail?

No — this MK136B engine is designed for 2018-2024 Softail models with M8 compatibility. Older Softails require different crate engines.

Is this street-legal?

No — S&S rates this engine for race-only use. It is not intended for street application.

What crankcases does this use?

Billet MKB-Series crankcases, which are matched to the 136-inch cylinder package and high-flow heads.

Does it come complete and ready to install?

Yes — all premium internal components, heads, covers, and necessary hardware are included. You provide the frame and ancillary systems.

What makes the valvetrain different from stock?

Valves are .030" longer with 1mm oversizes, premium springs rated to .605" lift, and improved geometry for high-RPM flow.