What is the primary benefit of installing these big bore cylinders?

The main advantage is a significant increase in engine displacement. This allows for more air and fuel to be processed, resulting in improved horsepower and torque output for your motorcycle.

Do I need special tools or machine work to install these cylinders?

No, these are designed as a direct bolt-on installation. They do not require any machine work on your crankcases or cylinder heads, making the installation process more accessible.

What is included with this pair of cylinders?

This kit includes the pair of big bore cylinders, which feature integrated cast iron liners. Cylinder head dowels are also included to ensure proper alignment during installation.

TwinPower Big Bore Cylinder Kit 4.25" Black 486959

Name: Twin Power 17-Up M8 Black 4.25 Inch Big Bore Cylinders Pair
Brand: TwinPower
Price: 693.24 USD
Availability: InStock

Twin Power 17-Up M8 Black 4.25 Inch Big Bore Cylinders Pair

$693.24

On Backorder — Expected to ship by Apr 22, 2026

Order now to reserve yours — we'll ship as soon as stock arrives. Full refund if we're unable to fulfill.

Twin Power 17-Up M8 Black 4.25 Inch Big Bore Cylinders Pair. Increases engine displacement for more power.

Key Features

Fits 33+ Harley-Davidson M8 vehicle makes and models.
Increases 107 cubic inch engines to 124 cubic inches.
Increases 114 cubic inch engines to 128 cubic inches.
Features cast iron liners for strength and durability.
Includes cylinder head dowels for proper alignment.
Direct bolt-on installation requires no crankcase or cylinder head machining.

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Will this fit your vehicle?

Product Details

If you're looking to get more out of your M8 engine, these big bore cylinders from Twin Power are a solid option. They're designed to increase the displacement of your stock 107 cubic inch engine to 124 cubic inches, or your 114 cubic inch engine to 128 cubic inches. This bump in size means more air and fuel can enter the combustion chamber, leading to a noticeable increase in power and torque. These cylinders fit a wide range of Harley-Davidson M8 models, including popular bikes like the Street Glide, Road King, and Heritage Classic.

Built with strength and durability in mind, these cylinders feature cast iron liners that are honed and ready to accept your pistons. The factory-style black textured powdercoat finish with highlighted fins gives them a clean, custom look that blends well with the M8 engine's aesthetic. A key benefit here is that they are a direct bolt-on installation, meaning you won't need to do any machine work on your crankcases or cylinder heads. This makes the upgrade process much more straightforward.

When you order this pair of cylinders, they come ready to go with cylinder head dowels included. This ensures proper alignment and a secure fit during installation. For anyone aiming to boost their M8's performance without extensive modifications, these big bore cylinders offer a well-built solution.