Wiseco PK1854 Forged Piston Kit 39mm Standard Bore 11:1 Compression Honda XR/CRF50

The Wiseco PK1854 is a high-performance forged piston kit designed for the Honda XR50 and CRF50F 50cc dirt bike engine. Built to a 39mm standard bore with an 11:1 compression ratio, this kit is a direct-fit upgrade that delivers measurably more power and durability over the stock cast piston—with no cylinder boring required.

As the only U.S. manufacturer of forged pistons for the motorsports market, Wiseco produces every piston in-house at its Mentor, Ohio facility. Starting with aerospace-grade aluminum, the forging process compresses and aligns the material's grain structure, resulting in a piston with superior tensile strength, impact resistance, and fatigue life compared to brittle cast alternatives. Every detail—from raw billet to final skirt coating—is controlled under one roof.

Kit Includes:

• Forged aluminum piston (39.00mm bore, Wiseco forging 4798M)
• Piston ring set
• Wrist pin
• Circlips

Key Specifications:

• Bore diameter: 39.00mm (standard bore)
• Compression ratio: 11:1
• Forging number: 4798M
• Construction: Forged aerospace-grade aluminum
• Finish: Skirt coating applied

Wiseco piston kits are engineered and tested on in-house dynos, ensuring each design delivers the optimum strength-to-weight ratio for competitive and recreational off-road riding. The PK1854 is a proven choice for rebuilding the top end of Honda's iconic 50cc mini bike platform.