S&S Big Bore Kit 128ci - M8 Oil Cooled

The Big Bore Cylinder Kit is a precision-engineered displacement upgrade designed for 114ci and 117ci oil-cooled Milwaukee-Eight engines. When used with the stock 4-1/2" stroke M-Eight crankshaft, this kit increases displacement by enlarging the bore—delivering noticeable gains in torque and horsepower while retaining excellent street reliability.

Designed to work efficiently with stock cylinder heads, this kit offers strong performance improvements without the complexity of head work or crankcase machining, making it an ideal bolt-on upgrade for performance-focused street builds.

Note: Installation requires a skilled technician. All clearances and assembly specifications must be checked during assembly. Not recommended for trike models.

Key Specifications

• Engine Compatibility: 114ci & 117ci Milwaukee-Eight (oil-cooled)

• Stroke: 4-1/2" (stock M-Eight stroke)

• Bore: Big-bore configuration (application-specific)

• Installation: Bolt-on (no case boring or splitting required, unless otherwise noted)

What’s Included

• Big Bore Cylinders

  • Premium aluminum castings

  • Cast-in iron liners for durability and heat control

• Pistons

  • Matched to cylinder bore for optimal performance

• Piston Rings

  • Complete ring set included

• Gasket Set

  • Cylinder head gaskets

  • Base gaskets

  • Exhaust gaskets

Highlights

• Delivers excellent results with stock cylinder heads

• Straightforward installation—swap cylinders, no crankcase machining

• Built for reliability and performance