S&S 107" to 129" Big Bore Kit for M8 Models

The S&S 107" to 129" Big Bore Kit is a high-performance engine upgrade designed to convert Gen 1 Harley-Davidson Milwaukee-Eight 107" engines with stock 4.375" stroke crankshafts to 129 cubic inches. Built for riders looking to add serious displacement, horsepower, and torque, this kit delivers a major performance increase for high-output M8 builds. Designed specifically for Gen 1 107" Milwaukee-Eight engines, featuring a 4.320" bore, forged pistons, an 11:1 compression ratio, this S&S Big Bore Kit gives riders a premium displacement upgrade while maintaining compatibility with stock 4.375" stroke crankshafts. Available in wrinkle black with highlighted fins or wrinkle black without highlighted fins, this kit delivers the performance and finish options needed to match your build.