OS 1.50 Piston Kit for the TRX 500 Foreman and Rubicon (2005–2011) is an oversize-bore replacement designed to restore compression and boost mid-life performance on these utility ATV engines. The +1.50 mm bore increases displacement for stronger torque and crisper throttle response, while still relying on a proper top-end rebuild for reliable operation. This aftermarket kit is built to deliver consistent power gains and lasting durability across the TRX 500 family without resorting to OEM pricing. It’s a practical refresh choice for trail work, farm tasks, or any mid-range rebuild where reliability matters.

Its oversized bore directly targets common wear patterns in the TRX 500 top end—reduced compression, ring seating loss, and diminished power—by restoring proper clearance and sealing. The kit is engineered to perform under the heat and vibration of tough trail rides and farm work, providing predictable, repeatable power gains. For both hobbyists and professional shops, this OS 1.50 kit offers a reliable route back to near-original performance during middle-life engine refreshes.

Comprehensive Vehicle Fitment

Product Specifications

OEM & Aftermarket Cross-Reference Information

What's Included

This kit includes the essential components needed to refresh the top end:

• Piston
• Rings Set
• Wrist Pin
• Circlips

Note: Related top-end gaskets, seals, and lubrication items are not included and may be required separately depending on your rebuild scope.

Why Choose This Aftermarket Replacement?

• Direct-Fit Compatibility: Engine-specific design for the TRX500 Foreman/Rubicon 2005–2011 minimizes fitment surprises and streamlines the top-end refresh.
• OEM Cross-Reference: Cross-references to Honda’s OEM part ensure alignment with factory specifications while offering a cost-effective aftermarket option.
• Premium Materials & Precision Machining: Built to tight tolerances and designed to withstand heat, friction, and vibration typical of mid-life top-end work.
• Performance Restoration: Restores compression and throttle response lost to piston and ring wear, delivering dependable mid-range power.
• Reliability in Tough Conditions: Designed for trail duty and farm work where durability and consistent performance matter most.
• Cost-Effective Refresh: A budget-conscious path to near-OEM performance without the premium price tag of factory parts.

Installation Notes:

• Drain oil and coolant as needed, then remove the cylinder head and inspect the bore for scoring, wear, and out-of-round conditions.
• Verify bore diameter and align the cylinder with the crankcase; oversized bore typically requires machine shop clearance and proper reassembly procedures.
• Check piston orientation marks and install the piston with correct orientation to ensure proper valve and connecting rod timing.
• Inspect and measure ring end gaps; if gaps are out of specification, adjust with the advised methods or replace rings as needed.
• Use fresh wrist pin clips and lubricate the wrist pin surfaces before installation to prevent galling and to ease seating.
• Follow a proper break-in procedure after install to seat rings and establish stable compression and sealing.

Why Upgrade?

Running a worn piston kit in this engine can lead to compression loss, reduced throttle response, higher oil consumption, and uneven power delivery. Replacing it with the OS 1.50 piston kit restores compression, improves throttle feel, and delivers reliable performance for continued trail and work-site use. This refresh helps protect the engine from further wear and preserves long-term reliability.