This piston kit is a standard-bore replacement for Yamaha YFM Kodiak 400 and Grizzly 400 utility ATVs, featuring an 84.5 mm bore and a ~401cc displacement. Designed for model years 2000 through 2008, it restores compression and dependable power delivery across the full RPM range, so you can tackle work tasks, trails, and farm duties with confidence. The kit is engineered to fit the original cylinder configuration without major rework, helping maintain factory-like throttle response and reliability after a rebuild.

Built for durability under demanding loads, this aftermarket piston kit delivers consistent performance and long service life when used in utility ATV applications. Its precisely machined parts and standard bore ensure reliable operation in the harsh environment of trail and farm use, making it a dependable choice for riders who demand steady power and easy maintenance.

Comprehensive Vehicle Fitment

Fitment notes and model coverage compiled from model cross-references and retailer product pages showing 84.5 mm standard bore kits for Kodiak 400 and Grizzly 400 platforms across 2000–2008.

Product Specifications

Spec data reflects standard-bore Yamaha Kodiak/Grizzly 400 kits with 84.5 mm bore and 10.5:1 compression, commonly listed as 401cc displacement. Cross-referenced OEM part numbers and common aftermarket equivalents are shown in retailer and parts catalogs.

OEM & Aftermarket Cross-Reference Information

Cross-reference data drawn from retailer catalogs and aftermarket suppliers showing 5GH-11631-00-00 as the standard bore piston kit reference and linking to alternative brands and part numbers.

What's Included

This kit includes the essential components to rebuild the top end for a 84.5 mm bore Yamaha Kodiak/Grizzly 400 cylinder:

• Piston (84.5 mm standard bore)
• Piston Ring Set
• Piston Wrist Pin (20 mm)
• Circlips (2x)

Note: Related gaskets and seals are not included in this piston-only kit.

Why Choose This Aftermarket Replacement?

• Direct-Fit Compatibility: 84.5 mm standard bore aligns with Yamaha Kodiak 400 and Grizzly 400 engines from 2000–2008, minimizing need for cylinder work in many rebuilds.
• OEM Cross-Reference: Clear cross-references to Yamaha part numbers and widely used aftermarket equivalents help confirm correct fitment.
• Premium Materials: Precision-machined aluminum alloy piston designed for strength, heat tolerance, and reliable ring seal.
• Performance Restoration: Restores compression and throttle response, delivering factory-like power across RPM ranges.
• Comprehensive Fitment Data: Widely used in 2000–2008 Kodiak/Grizzly platforms, with documented 401cc displacement and 10.5:1 compression.
• Durability for Work & Trail: Engineered to endure the demands of utility riding, hauling, and rugged trail use.

Installation Notes:

• Inspect the cylinder bore for wear and ensure proper piston-to-wall clearance before installing the new piston kit.
• Confirm 84.5 mm bore and orientation of the piston, rings, and wrist pin during assembly to maintain correct timing and sealing.
• Use the correct piston ring end gaps per your bore size and verify ring seating with even compression during initial startup.
• Install wrist pin clips securely; ensure they are seated to prevent pin migration under load.
• Lubricate the piston skirts and rings with appropriate oil before initial startup and allow a proper break-in period under light load.
• Double-check torque and fastener specs for related components (gaskets, head cover, and related top-end hardware) during reassembly.

Why Upgrade?

Running a worn piston kit in these 400-class engines increases blow-by, compression loss, and inconsistent power delivery, especially under load. Replacing with a new standard-bore piston kit restores compression, throttle response, and overall reliability, helping your Kodiak or Grizzly perform like new under work, trail, and farm conditions.