TB Parts 149cc Big Bore Kit, 55mm Forged Piston, & Cam – 2022+ Grom/Monkey 125

TBparts 149cc Big Bore Kit with Forged Piston & Performance Cam – 2022+ Honda Grom/Monkey 125

Unleash the full potential of your 2022+ Honda Grom or Monkey 125 with the TBparts 149cc Big Bore Kit! Designed for riders looking for a serious performance boost, this kit delivers increased power, higher compression, and a more exhilarating ride—all at an unbeatable price.

Featuring a 55mm forged piston, this bolt-on upgrade significantly enhances throttle response and torque. Plus, there’s no need for case boring—just install, tune (tuning not included), and hit the road! Whether you're upgrading for more power or simply rebuilding your engine with fresh components, this kit is the perfect solution.

For even more performance, we’ve included our high-lift camshaft, designed specifically for the Grom, Monkey, CT125, Dax, and Cub. This cam opens the valves wider and faster, allowing more air and fuel into the engine—translating to even more power and quicker acceleration.

 Key Features:
✔ 149cc big bore kit – More displacement, more power!
✔ 55mm forged piston – Increased durability and compression 11.8:1 pump 91+ octane friendly
✔ Bolt-on installation – No case boring required.
✔ Performance camshaft included – Maximized airflow for peak performance.
✔ Perfect for street and track riders – Unlock hidden horsepower!

Take your ride to the next level with the TBparts 149cc Big Bore Kit & Performance Cam—because stock just isn’t enough!

There are no installation instructions, but if you can replace your piston, you can install this kit. If you don’t have any experience working on your engine, we highly recommend having a professional technician install this kit or, at a minimum, purchasing the shop manual for your bike. We also have a link on our website in the INFO section under Honda where you can find additional info. The parts are installed in the same manner as the OEM parts.

Notes:

• These bore kits are only for the 2022 and newer models (will not work on the 2021 and older models as the engine has been redesigned)
• A performance intake and exhaust is recommended if you want to get the most power possible! (Not necessary)
• Tuning Required – The ECU will require a flash/tune to prevent a lean condition and possible damage to your engine. CJR Performance (cameronjonesracing.com) provides this service and can also adjust the tune based on your other modifications.
• Valve Lash Settings – 0.003″ Intake/Exhaust

This product is legal for closed-course competition use only; for racing vehicles (a competition vehicle not used on public highways). Intended for off-road use or race purposes; may not meet regulations of pollution controlled roads or highways. Not legal for vehicles registered and use in California.