89mm 440cc Big Bore Cylinder Kit for Honda XR400R TRX400EX TRX400X

Product Overview

Upgrade or rebuild your compatible Honda 400cc engine with this 89mm big bore cylinder and piston kit, designed for selected XR400R, TRX400EX, and TRX400X applications.

Featuring an enlarged 89mm cylinder bore, this kit is commonly marketed as a 440cc big bore conversion for compatible Honda 400-series engines. The kit includes the cylinder, matched piston components, gaskets, and spark plug needed for a top-end installation.

This is a big bore modification kit, not a standard-bore OEM replacement cylinder. Engine setup, clearances, fuel delivery, and other supporting components should be checked during installation.

Product Compatibility

Make	Model	Year Range	Application
Honda	XR400R	1996–2004	89mm Big Bore Conversion
Honda	TRX400EX Sportrax / 400EX	1999–2008	89mm Big Bore Conversion
Honda	TRX400X	2009	89mm Big Bore Conversion
Honda	TRX400X	2012–2014	89mm Big Bore Conversion

Note: TRX400X model years 2010–2011 are not included in the listed application range.

Fitment should be confirmed by model, year, cylinder configuration, mounting dimensions, and original engine components before ordering.

OEM Cross-Reference Numbers

Honda Cylinder Reference

• 12100-HN1-A70

This aftermarket 89mm big bore cylinder is not an OEM-standard-bore cylinder. The OEM number above should be treated as an application/reference number rather than a claim that the 89mm cylinder has original Honda bore specifications.

Specifications

Specification	Details
Product Type	Big Bore Cylinder & Piston Kit
Application	ATV / Off-Road Motorcycle
Engine Type	4-Stroke
Cylinder Bore	89 mm / 3.50 in
Marketed Displacement	440cc Big Bore
Original Engine Class	400cc
Listed Mounting Distances	Approx. 87 × 80 × 90 × 80 mm
Inch Equivalents	Approx. 3.43 × 3.15 × 3.54 × 3.15 in
Cylinder Design	Enlarged Sleeve / Big Bore
Condition	New

Key Features

• 89mm Big Bore: Enlarged cylinder bore for compatible Honda XR400R, TRX400EX, and TRX400X engines.
• 440cc-Class Conversion: Commonly marketed as a 440cc upgrade from the original 400cc engine configuration.
• Matched Top-End Components: Includes cylinder, piston components, gaskets, and spark plug for a compatible installation.
• Larger Cylinder Sleeve: Designed specifically for the increased 89mm bore configuration.
• Multiple Honda Applications: Covers selected XR400R, TRX400EX, and TRX400X model years.