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Upgrade your 107-inch M8 engine with the S&S Cycle 129" Power Package, part number 310-1398, designed to boost performance without requiring case modifications. This comprehensive big bore bolt-on kit features a 4.320-inch cylinder and 11.0:1 forged pistons, delivering increased displacement for enhanced power and acceleration. The package includes an HPT496 cam optimized for big bore applications, providing improved torque and top-end performance while maintaining the stock engine height and compatibility with original engine serial numbers. Built with precision, the kit retains the stock crankcases and works seamlessly with stock and S&S roller rocker arms, ensuring a straightforward installation process for experienced builders and enthusiasts alike.
Constructed from high-quality materials, this system features a multi-layered steel (MLS) head gasket for reliable sealing and durability. The included oil pump and cam plate are designed for efficient oil flow, with independent scavenge sections for the flywheel cavity and cam chest, along with debris screens in both pickups to prevent contaminants from entering the system. An adjustable pressure relief valve allows fine-tuning of oil pressure without removing the unit from the engine, maintaining optimal lubrication under various operating conditions. The package also offers Quickee pushrods with pushrod tubes, premium S&S tappets, and hard anodized, black-coated billet aluminum tappet cuffs—these components ensure durability and smooth operation.
The system is equipped with high-performance conical single-wire valve springs compatible with cams up to 0.605-inch lift, along with a magnet in the cam chest to prevent debris from damaging the oil pump. This gear drive system is oil cooled and features a sleek black finish with highlights, providing a professional look that complements your bike’s aesthetic. Designed and manufactured in the USA, this kit maintains stock valve spring compatibility for both first-generation (round port) and second-generation (oval port) cylinders, offering versatile application for a range of Harley-Davidson models. Whether you're seeking increased power or durability, the S&S Cycle 129" Power Package delivers a reliable, high-performance upgrade for your M8 engine.
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