Vertex VTK24370B Top End Piston Kit — 2002-2018 Yamaha YZ85 | Size B (47.45mm)

Vertex Pistons — Precision Cast Replica, Molybdenum Disulphite Skirt Coating, and Complete Top-End Restoration

Restore the compression and high-revving performance of your mini-racer with the Vertex VTK24370B Top End Piston Kit. Specifically engineered for the 2002-2018 Yamaha YZ85, this kit is the professional choice for a complete top-end overhaul. Vertex pistons are the premier OE replacement choice, offering a precision cast replica design that matches the factory engine's power characteristics while incorporating modern material advancements for superior longevity.

Every Vertex piston is gravity-cast from a specialized aluminum alloy with an 18% silicone content. This high silicone level is critical; it reduces thermal expansion, allowing for tighter tolerances and preventing the piston from "growing" and seizing at high temperatures. To ensure maximum durability, the piston undergoes a T-5 hardening and tempering cycle. Additionally, the skirt is treated with a high-tech Molybdenum Disulphite coating, which facilitates a faster break-in period and provides an extra layer of protection during high-RPM operation. This comprehensive kit includes everything needed for the job: the B-series piston (47.45mm), rings, wrist pin, circlips, a complete top-end gasket set, and a new wrist pin bearing.

• Comprehensive Top End Kit: Includes piston, rings, pin, circlips, top-end gaskets, and a high-quality wrist pin bearing.
• High Silicone Alloy: 18% silicone content reduces thermal expansion and increases wear resistance compared to standard cast pistons.
• Molybdenum Disulphite Coating: High-tech skirt coating reduces friction, eases break-in, and extends piston life.
• T-5 Heat Treatment: Hardening and tempering cycle ensures the piston retains its structural integrity under extreme racing loads.
• Precision B-Sizing: 47.45mm diameter designed for 47.50mm cylinders that have seen moderate use, ensuring optimal clearance.

Moto-House MX Pro Tip:

Top end maintenance is the lifeblood of a 2-stroke YZ85. When installing the Vertex VTK24370B kit, cleanliness is your best friend. Thoroughly clean the power valve assembly and the cylinder bore before assembly. Always check your ring end-gap to ensure it meets factory specifications. This kit includes the Size B (47.45mm) piston, which is often preferred for cylinders that are slightly worn but still within the 47.50mm standard limit to maintain a perfect seal. Never reuse old circlips—always use the fresh ones provided in the kit to prevent catastrophic engine failure.

Technical Specification	Details
Piston Diameter	47.45 mm (Size B)
Cylinder Diameter	47.50 mm
Material	18% Silicone Aluminum Alloy
Kit Contents	Piston, Rings, Pin, Clips, Gaskets, Bearing

FAQ Questions

Q) Why choose a Size B piston?
A) As a cylinder is used, it wears slightly. A "B" piston is 0.01mm larger than an "A" piston to take up that minute wear and restore proper piston-to-wall clearance without needing a re-plate.

Q) Is this piston forged or cast?
A) This is a gravity-cast replica piston, designed to match OEM specifications while offering superior wear characteristics due to its high silicone content.

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