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S&S Cycle M8 129 in. Big Bore Kits
2017+ M8 Models 129in Big-Bore Kit 4.375in Stroke Highlighted Cylinders
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Estimated Ship Date: Dec 16, 2026 Would you rather pick it up?
Overview
Brand:
Manufacturer's Part Number:
910-0843A
Part Type:
Product Line:
Summit Racing Part Number:
SSY-910-0843A
Cylinder Included:
Yes
Pistons Included:
Yes
Piston Material:
Forged aluminum
Piston Rings Included:
Yes
Wrist Pin Included:
Yes
Wrist Pin Bearing Included:
No
Head Gaskets Included:
Yes
Base Gaskets Included:
Yes
Cam Chain Tensioner Gaskets Included:
No
Exhaust Gaskets Included:
No
Valve Cover Gaskets Included:
No
Quantity:
Sold as a kit.
Notes:
Cylinders are wrinkle black with highlighted fins.
S&S Cycle M8 129 in. Big Bore Kits
The S&S Cycle M8 129 in. Big Bore kits are a high performance engine upgrade for Harley-Davidson Milwaukee-Eight 107 in. engines, designed to increase displacement to 129 cu. in. They are bolt-on kits that require no crankcase machining or engine removal, featuring a 4.32 in. bore, 11:1 compression ratio, and forged pistons. Available with highlighted or non-highlighted cylinders.
Key details:
* Massive performance increase: Transforms the 107 in. engine into a high-torque 129 in. powerplant
* Bolt-on installation: Installs without boring the engine cases, saving machine work costs
* Retains stock components: Fits with stock heads, flywheels, and retains stock engine height
* Durability: Features aluminum cylinders with cast iron sleeves for better durability
* Pump gas compatible: Despite the high compression (11:1), it is designed for pump gas
* Wrinkle black powdercoat finish to match factory engines.
Kit contents:
* 4.32 in. Big Bore cylinders
* Forged pistons with rings
* MLS (Multi-Layered Steel) head gaskets
* Includes cam cover badge
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