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

High-quality cast Big Bore Cylinders from Twin Power™. Factory style black textured powdercoat finish with highlighted fins. Cast in iron liners for strength and durability and finish honed and ready to run.

• Direct bolt-on, requires no machine work to crankcases or cylinder heads
• Increases 107 in. engines to 124 in. and 114 in. engines to 128 in.
• Includes cylinder head dowels
• Sold in pairs

Upgrade your Milwaukee-Eight engine with Twin Power Big Bore Cylinders, part number twp486959. Designed as a direct bolt-on replacement, these high-quality cast cylinders increase 107-cubic-inch engines to 124 cubic inches and 114-cubic-inch engines to 128 cubic inches without requiring machining to the crankcases or cylinder heads. The cylinders are finished in a factory-style black textured powder coat with highlighted cooling fins for a clean, performance-focused appearance.
Built with cast-in iron liners, these cylinders provide strength and durability for demanding powersports applications. Each cylinder is finish honed and ready to run, helping simplify installation and reduce preparation time. Cylinder head dowels are included to support proper fitment during assembly, and the set is sold in pairs for a complete engine upgrade. This Twin Power kit is intended for select 2017 and newer Harley-Davidson Milwaukee-Eight applications.
Fitment includes the 2017 Harley-Davidson FLHR Road King, FLHX Street Glide, FLTRX Road Glide, FLHXS Street Glide Special, FLTRXS Road Glide Special, FLHTCU Electra Glide Ultra Classic, FLTRU Road Glide Ultra, FLHTK Ultra Limited, and FLHTKL Ultra Limited Low, as well as the 2018 Harley-Davidson FLHR Road King. Verify your motorcycle model, engine configuration, and installation requirements before ordering. Professional installation is recommended for engine performance components.

Features:

• Direct bolt-on design: Installs without machining the crankcases or cylinder heads

• Engine displacement upgrade: Converts 107-cubic-inch engines to 124 cubic inches and 114-cubic-inch engines to 128 cubic inches

• Durable construction: Cast-in iron liners provide strength and long-term durability

• Ready to run: Finish honed for simplified installation

• Factory-style finish: Black textured powder coat with highlighted cooling fins

• Complete set: Includes cylinder head dowels and is sold in pairs

• Application: Designed for select 2017 and newer Harley-Davidson Milwaukee-Eight models

Fitment:
Harley Davidson FLDE Deluxe 107 Base 2018
Harley Davidson FLDE Deluxe 107 Base 2019
Harley Davidson FLDE Deluxe 107 Base 2020
Harley Davidson FLFB Fat Boy 107 Base 2018
Harley Davidson FLFB Fat Boy 107 Base 2019
Harley Davidson FLFBS Fat Boy 114 Base 2018
Harley Davidson FLFBS Fat Boy 114 Base 2019
Harley Davidson FLFBS Fat Boy 114 Base 2020
Harley Davidson FLFBS Fat Boy 114 Base 2021
Harley Davidson FLH Electra Glide Revival Base 2021
Harley Davidson FLHC Heritage Classic 107 Base 2018
Harley Davidson FLHC Heritage Classic 107 Base 2019
Harley Davidson FLHC Heritage Classic 107 Base 2020
Harley Davidson FLHC Heritage Classic 107 Base 2021
Harley Davidson FLHCS Heritage Classic 114 Base 2018
Harley Davidson FLHCS Heritage Classic 114 Base 2019
Harley Davidson FLHCS Heritage Classic 114 Base 2020
Harley Davidson FLHCS Heritage Classic 114 Base 2021
Harley Davidson FLHR Road King Base 2017
Harley Davidson FLHR Road King Base 2018
Harley Davidson FLHR Road King Base 2019
Harley Davidson FLHR Road King Base 2020
Harley Davidson FLHR Road King Base 2021
Harley Davidson FLHRXS Road King Special Base 2017
Harley Davidson FLHRXS Road King Special Base 2018
Harley Davidson FLHRXS Road King Special Base 2019
Harley Davidson FLHRXS Road King Special Base 2020
Harley Davidson FLHRXS Road King Special Base 2021
Harley Davidson FLHT Electra Glide Standard Base 2019
Harley Davidson FLHT Electra Glide Standard Base 2020
Harley Davidson FLHT Electra Glide Standard Base 2021
Harley Davidson FLHTCU Electra Glide Ultra Classic Base 2017
Harley Davidson FLHTCU Electra Glide Ultra Classic Base 2018
Harley Davidson FLHTCU Electra Glide Ultra Classic Base 2019
Harley Davidson FLHTCUTG Tri Glide Ultra Base 2017
Harley Davidson FLHTCUTG Tri Glide Ultra Base 2018
Harley Davidson FLHTCUTG Tri Glide Ultra Base 2019
Harley Davidson FLHTCUTG Tri Glide Ultra Base 2020
Harley Davidson FLHTCUTG Tri Glide Ultra Base 2021
Harley Davidson FLHTCUTGSE CVO Tri Glide Base 2020
Harley Davidson FLHTCUTGSE CVO Tri Glide Base 2021
Harley Davidson FLHTK Ultra Limited Base 2017
Harley Davidson FLHTK Ultra Limited Base 2018
Harley Davidson FLHTK Ultra Limited Base 2019
Harley Davidson FLHTK Ultra Limited Base 2020
Harley Davidson FLHTK Ultra Limited Base 2021
Harley Davidson FLHTKL Ultra Limited Low Base 2017
Harley Davidson FLHTKL Ultra Limited Low Base 2018
Harley Davidson FLHTKL Ultra Limited Low Base 2019
Harley Davidson FLHTKSE CVO Limited Base 2017
Harley Davidson FLHTKSE CVO Limited Base 2018
Harley Davidson FLHTKSE CVO Limited Base 2019
Harley Davidson FLHTKSE CVO Limited Base 2020
Harley Davidson FLHTKSE CVO Limited Base 2021
Harley Davidson FLHX Street Glide Base 2017
Harley Davidson FLHX Street Glide Base 2018
Harley Davidson FLHX Street Glide Base 2019
Harley Davidson FLHX Street Glide Base 2020
Harley Davidson FLHX Street Glide Base 2021
Harley Davidson FLHXS Street Glide Special Base 2017
Harley Davidson FLHXS Street Glide Special Base 2018
Harley Davidson FLHXS Street Glide Special Base 2019
Harley Davidson FLHXS Street Glide Special Base 2020
Harley Davidson FLHXS Street Glide Special Base 2021
Harley Davidson FLHXSE CVO Street Glide Base 2017
Harley Davidson FLHXSE CVO Street Glide Base 2018
Harley Davidson FLHXSE CVO Street Glide Base 2019
Harley Davidson FLHXSE CVO Street Glide Base 2020
Harley Davidson FLHXSE CVO Street Glide Base 2021
Harley Davidson FLRT Freewheeler Base 2017
Harley Davidson FLRT Freewheeler Base 2018
Harley Davidson FLRT Freewheeler Base 2019
Harley Davidson FLRT Freewheeler Base 2020
Harley Davidson FLRT Freewheeler Base 2021
Harley Davidson FLSB Sport Glide 107 Base 2018
Harley Davidson FLSB Sport Glide 107 Base 2019
Harley Davidson FLSB Sport Glide 107 Base 2020
Harley Davidson FLSB Sport Glide 107 Base 2021
Harley Davidson FLSL Softail Slim 107 Base 2018
Harley Davidson FLSL Softail Slim 107 Base 2019
Harley Davidson FLSL Softail Slim 107 Base 2020
Harley Davidson FLSL Softail Slim 107 Base 2021
Harley Davidson FLTRK Road Glide Limited Base 2020
Harley Davidson FLTRK Road Glide Limited Base 2021
Harley Davidson FLTRU Road Glide Ultra Base 2017
Harley Davidson FLTRU Road Glide Ultra Base 2018
Harley Davidson FLTRU Road Glide Ultra Base 2019
Harley Davidson FLTRX Road Glide Base 2017
Harley Davidson FLTRX Road Glide Base 2018
Harley Davidson FLTRX Road Glide Base 2019
Harley Davidson FLTRX Road Glide Base 2020
Harley Davidson FLTRX Road Glide Base 2021
Harley Davidson FLTRXS Road Glide Special Base 2017
Harley Davidson FLTRXS Road Glide Special Base 2018
Harley Davidson FLTRXS Road Glide Special Base 2019
Harley Davidson FLTRXS Road Glide Special Base 2020
Harley Davidson FLTRXS Road Glide Special Base 2021
Harley Davidson FLTRXSE CVO Road Glide Base 2018
Harley Davidson FLTRXSE CVO Road Glide Base 2019
Harley Davidson FLTRXSE CVO Road Glide Base 2020
Harley Davidson FLTRXSE CVO Road Glide Base 2021
Harley Davidson FXBB Street Bob 107 Base 2018
Harley Davidson FXBB Street Bob 107 Base 2019
Harley Davidson FXBB Street Bob 107 Base 2020
Harley Davidson FXBBS Street Bob 114 Base 2021
Harley Davidson FXBR Breakout 107 Base 2018
Harley Davidson FXBR Breakout 107 Base 2019
Harley Davidson FXBRS Breakout 114 Base 2018
Harley Davidson FXBRS Breakout 114 Base 2019
Harley Davidson FXBRS Breakout 114 Base 2020
Harley Davidson FXDRS FXDR 114 Base 2019
Harley Davidson FXDRS FXDR 114 Base 2020
Harley Davidson FXFB Fat Bob 107 Base 2018
Harley Davidson FXFB Fat Bob 107 Base 2019
Harley Davidson FXFBS Fat Bob 114 Base 2018
Harley Davidson FXFBS Fat Bob 114 Base 2019
Harley Davidson FXFBS Fat Bob 114 Base 2020
Harley Davidson FXFBS Fat Bob 114 Base 2021
Harley Davidson FXLR Low Rider 107 Base 2018
Harley Davidson FXLR Low Rider 107 Base 2019
Harley Davidson FXLR Low Rider 107 Base 2020
Harley Davidson FXLRS Low Rider S 114 Base 2020
Harley Davidson FXLRS Low Rider S 114 Base 2021
Harley Davidson FXST Softail Standard 107 Base 2020
Harley Davidson FXST Softail Standard 107 Base 2021
Harley-Davidson FLFBS Fat Boy 114 Base 2022
Harley-Davidson FLFBS Fat Boy 114 Base 2023
Harley-Davidson FLFBS Fat Boy 114 Base 2024
Harley-Davidson FLHC Heritage Classic 117 Base 2025
Harley-Davidson FLHCS Heritage Classic 114 Base 2022
Harley-Davidson FLHCS Heritage Classic 114 Base 2023
Harley-Davidson FLHCS Heritage Classic 114 Base 2024
Harley-Davidson FLHFB Electra Glide Highway King Base 2023
Harley-Davidson FLHR Road King Base 2022
Harley-Davidson FLHRXS Road King Special Base 2022
Harley-Davidson FLHRXS Road King Special Base 2023
Harley-Davidson FLHRXS Road King Special Base 2024
Harley-Davidson FLHRXS Road King Special Base 2025
Harley-Davidson FLHT Electra Glide Standard Base 2022
Harley-Davidson FLHTCUTG Tri Glide Ultra Base 2022
Harley-Davidson FLHTCUTG Tri Glide Ultra Base 2023
Harley-Davidson FLHTCUTG Tri Glide Ultra Base 2024
Harley-Davidson FLHTCUTG Tri Glide Ultra Base 2025
Harley-Davidson FLHTCUTG Tri Glide Ultra G.I. Base 2022
Harley-Davidson FLHTCUTGSE CVO Tri Glide Base 2022
Harley-Davidson FLHTK Ultra Limited Base 2022
Harley-Davidson FLHTK Ultra Limited Base 2023
Harley-Davidson FLHTK Ultra Limited Base 2024
Harley-Davidson FLHX Street Glide Base 2022
Harley-Davidson FLHX Street Glide Base 2023
Harley-Davidson FLHX Street Glide Base 2024
Harley-Davidson FLHX Street Glide Base 2025
Harley-Davidson FLHXS Street Glide Special Base 2022
Harley-Davidson FLHXS Street Glide Special Base 2023
Harley-Davidson FLHXSE CVO Street Glide Base 2022
Harley-Davidson FLHXSE CVO Street Glide Base 2023
Harley-Davidson FLHXSE CVO Street Glide Base 2024
Harley-Davidson FLHXSE CVO Street Glide Base 2025
Harley-Davidson FLHXST Street Glide ST Base 2022
Harley-Davidson FLHXST Street Glide ST Base 2023
Harley-Davidson FLHXU Street Glide Ultra Base 2025
Harley-Davidson FLI Hydra-Glide Revival Base 2024
Harley-Davidson FLRT Freewheeler Base 2022
Harley-Davidson FLRT Freewheeler Base 2023
Harley-Davidson FLRT Freewheeler Base 2024
Harley-Davidson FLRT Freewheeler Base 2025
Harley-Davidson FLSB Sport Glide 107 Base 2022
Harley-Davidson FLSB Sport Glide 107 Base 2023
Harley-Davidson FLSB Sport Glide 107 Base 2024
Harley-Davidson FLSTFI Fat Boy Gray Ghost Base 2025
Harley-Davidson FLTRK Road Glide Limited Base 2022
Harley-Davidson FLTRK Road Glide Limited Base 2023
Harley-Davidson FLTRK Road Glide Limited Base 2024
Harley-Davidson FLTRKSE CVO Road Glide Limited Base 2022
Harley-Davidson FLTRKSE CVO Road Glide Limited Base 2023
Harley-Davidson FLTRT Road Glide 3 Base 2023
Harley-Davidson FLTRT Road Glide 3 Base 2024
Harley-Davidson FLTRT Road Glide 3 Base 2025
Harley-Davidson FLTRX Road Glide Base 2022
Harley-Davidson FLTRX Road Glide Base 2023
Harley-Davidson FLTRX Road Glide Base 2024
Harley-Davidson FLTRX Road Glide Base 2025
Harley-Davidson FLTRXRRSE CVO Road Glide RR Base 2025
Harley-Davidson FLTRXS Road Glide Special Base 2022
Harley-Davidson FLTRXS Road Glide Special Base 2023
Harley-Davidson FLTRXSE CVO Road Glide Base 2022
Harley-Davidson FLTRXSE CVO Road Glide Base 2023
Harley-Davidson FLTRXSE CVO Road Glide Base 2024
Harley-Davidson FLTRXSE CVO Road Glide Base 2025
Harley-Davidson FLTRXST Road Glide ST Base 2022
Harley-Davidson FLTRXST Road Glide ST Base 2023
Harley-Davidson FLTRXSTSE CVO Road Glide ST Base 2024
Harley-Davidson FLTRXSTSE CVO Road Glide ST Base 2025
Harley-Davidson FXBB Street Bob 117 Base 2025
Harley-Davidson FXBBS Street Bob 114 Base 2022
Harley-Davidson FXBBS Street Bob 114 Base 2023
Harley-Davidson FXBBS Street Bob 114 Base 2024
Harley-Davidson FXBR Breakout 117 Base 2023
Harley-Davidson FXBR Breakout 117 Base 2024
Harley-Davidson FXBR Breakout 117 Base 2025
Harley-Davidson FXFB Fat Bob 107 Base 2020
Harley-Davidson FXFBS Fat Bob 114 Base 2022
Harley-Davidson FXFBS Fat Bob 114 Base 2023
Harley-Davidson FXLRS Low Rider S 117 Base 2022
Harley-Davidson FXLRS Low Rider S 117 Base 2023
Harley-Davidson FXLRS Low Rider S 117 Base 2024
Harley-Davidson FXLRS Low Rider S 117 Base 2025
Harley-Davidson FXLRST Low Rider ST 117 Base 2022
Harley-Davidson FXLRST Low Rider ST 117 Base 2023
Harley-Davidson FXLRST Low Rider ST 117 Base 2024
Harley-Davidson FXLRST Low Rider ST 117 Base 2025
Harley-Davidson FXRST Low Rider El Diablo 117 Base 2022
Harley-Davidson FXST Softail Standard 107 Base 2022
Harley-Davidson FXST Softail Standard 107 Base 2023
Harley-Davidson FXST Softail Standard 107 Base 2024