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 MKB-series crankcases with high-flow cylinder heads and premium valvetrain components. Ready to bolt into your M8 Softail frame as a direct replacement for maximum displacement and reliability.

Features

• 136 cubic inches displacement
• High-flow cylinder heads with premium seats and guides
• +1mm intake and exhaust valves
• .605" max lift valve springs
• Valves .030" longer than stock for improved geometry
• Billet aluminum covers
• High-strength alloy cylinder head casting

Specifications

• Brand: S&S Cycle
• Manufacturer Part #: 310-1296
• Displacement: 136 cubic inches
• Category: Engine Components / Engines
• Weight: 135 lb

Fitment

Fits 2018-2024 Harley-Davidson Softail models with Milwaukee-Eight (M8) mounting points.

Frequently Asked Questions

Will this engine fit my Softail?

Yes — fits all 2018-2024 Harley-Davidson Softail models as a direct M8 engine swap.

What's included in the crate engine?

Complete assembled engine with high-flow heads, premium valvetrain, and sprocket shaft spacer. Ready to install into your frame.

Does this require custom tuning?

A professional fuel mapping and tune is recommended to optimize performance with the larger displacement and high-flow heads.

How much horsepower does the MK136B make?

Horsepower varies by tune and fuel octane. Contact S&S Cycle or your installer for certified dyno results.

Is this covered by warranty?

S&S Cycle offers limited warranty on crate engines. Check the warranty terms with your dealer or S&S directly.