Harley Screamin Eagle Piston Kit 4.310" Bore x 4.375" Stroke '17+Touring Softail
Part number 21900101 a Screamin' Eagle High Compression Piston Kit from Harley-Davidson, which is a replacement part for models equipped with the 128CI Stage IV or specific 122CI Stage III performance kits.
Product Specifications
Bore and Stroke: 4.310" bore x 4.375" stroke.
Compression Ratio: Increases the engine's compression to 10.9:1 when used with compatible components.
Material: The pistons are forged from high-strength aluminum and feature precision-machined, coated skirts for a tight-tolerance fit and quieter operation.
Contents: The complete kit includes two pistons, rings, wrist pins, and clips.
Regulatory Status: These are 50-State U.S. EPA compliant for sale and use on all applicable vehicles.
The Screamin' Eagle part number 21900101 high-compression piston kit is a replacement part for Milwaukee-Eight 107ci engines that have been upgraded with a 128CI Stage IV performance kit, or certain 122CI Stage III kits.
Compatible Models
The kit fits specific Harley-Davidson models that are already running the appropriate large bore engine upgrades:
Touring Models: Fits 2017–2024 Harley-Davidson Touring models originally equipped with a 107ci Milwaukee-Eight engine that has been upgraded with a 128CI Stage IV kit.
Excludes: Trike models.
Softail Models: Fits 2018–2024 Harley-Davidson Softail models originally equipped with a 107ci Milwaukee-Eight engine that has been upgraded with a 128CI Stage IV kit.
2025-later Touring Models: For 2025 and later models, this piston set is also used in the 122CI Stage III kit for the Street Glide (FLHX), Road Glide (FLTRX), and Street Glide Ultra (FLHXU) models.
Key Fitment Notes
Engine Upgrade Required: This is a replacement piston kit for an already modified engine; it is not intended for stock 107ci engines on its own.
Bore and Stroke: The pistons are designed for a 4.310" bore and 4.375" stroke.
ECM Recalibration: All installations and replacements require an Engine Control Module (ECM) calibration with a Screamin' Eagle Pro Street Tuner for proper operation.
Exhaust Systems: Certain models may require the separate purchase of a specific high-flow exhaust system for proper fitment.
Selling as pictured.
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010826-JM8